Dual-circuit or single-circuit gas boiler: what is the difference, what is better, what are the differences and how to choose correctly

The selection of an appropriate heating system is essential for maintaining a warm and comfortable living environment. Gas boilers are a standout option due to their efficiency and dependability. However, there is a decision to be made within this category between dual-circuit and single-circuit gas boilers. Knowing the distinctions between these two kinds will enable you to choose wisely for your house.

What distinguishes these boilers specifically, then? Let’s dissect it. The only purpose of a single-circuit gas boiler is to heat your house. It heats water, which warms your living area by circulating it through your radiators or underfloor heating system. Conversely, a dual-circuit gas boiler generates hot water for your shower and faucets in addition to heating. For homes that require more hot water, this dual functionality may be useful.

Which is better for you, though? Your unique requirements and preferences will determine the response. A single-circuit boiler might work well in a smaller home with minimal hot water consumption. Its design is usually simpler, and it could be more affordable in terms of initial outlay and ongoing maintenance. A dual-circuit boiler, on the other hand, might be a better option if you have a larger family or frequently need a large amount of hot water because it provides the convenience of hot water on demand.

Let’s now examine the functional distinctions between these two kinds of boilers. Since a single-circuit boiler only has to heat water for the central heating system, its construction is typically simpler. Over time, this simplicity may result in less expensive maintenance and simpler installation. However, because a dual-circuit boiler has to effectively control both the production of hot water and heat, it is more complicated. This complexity provides the convenience of a constant supply of hot water, but it may also result in higher initial costs and possibly more maintenance.

So, how can one select the ideal boiler for their house? First, determine how much hot water and heating your home requires. Think about things like how big your house is, how many people live there, and how often you use the hot water. Speaking with a licensed heating engineer can also yield insightful advice and suggestions catered to your unique situation. Ultimately, whether you choose a single- or dual-circuit gas boiler, making sure the installation is done correctly and that it is maintained on a regular basis will help to maximize its lifespan and efficiency and keep your house toasty and cozy for many years to come.

Dual-circuit Gas Boiler	Single-circuit Gas Boiler
Has separate circuits for heating and hot water	Only one circuit for both heating and hot water
Provides hot water on demand, even if heating is off	Hot water is available only when heating is on
More efficient for homes with high hot water demand	Simpler and may be more cost-effective for smaller homes
Higher initial cost but potential long-term savings on energy bills	Lower initial cost but may lead to higher energy bills in some cases
Ideal for larger households or homes with multiple bathrooms	Suitable for smaller households with lower hot water usage
Requires more space for installation due to separate components	Compact design, requires less space for installation
Choosing depends on household size, hot water needs, and budget	Choosing depends on simplicity, space availability, and budget constraints

What is the difference between a two-circuit boiler and a single-circuit boiler?

In contrast to a single-circuit boiler, a two-circuit boiler has an integrated flow water heater that supplies hot water as well as heat to the home. It is actually a case that holds two appliances. Hot water supply can, however, be handled by a single-circuit boiler; more on that a little later.

Electric two-circuit boilers are not common because they require special wiring, consume a lot of energy, put a lot of strain on the power grid, and have very high heating and hot water expenses.

It is essential to automatically regulate the heat output of a flow water heater, which is a component of a two-circuit boiler, in accordance with the hot water flow rate. Consequently, the most prevalent type of fuel-fired two-circuit boilers are those that run on gas. Additionally, there are diesel two-circuit boilers, in which an automatic system controls the burner’s liquid fuel supply.

Although solid fuel combustion intensities cannot be dynamically controlled, solid fuel two-circuit boilers do exist. They employ the pyrolysis process, which releases combustible gas from solid fuel by heating it to a high temperature without the presence of oxygen. After that, everything proceeds exactly as it would in a gas boiler. Heat and hot water boilers powered by solid fuels, such as wood, coal, or peat, can be highly economical in regions where these fuels are readily available and affordable.

Because they don’t have an integrated flow water heater, single-circuit boilers have a simpler design. Boilers with a single circuit are classified as electric, diesel, solid fuel, or gas boilers based on the type of energy they use. Due to their affordability, effectiveness, and convenience, gas boilers—both single- and double-circuit—are the most widely used these days. Furthermore, gas fuel conversions of diesel and solid fuel boilers are common. Thus, we will primarily discuss gas boilers in the future, as they are available in a wide variety of models.

The main differences

The primary distinction between a single- and two-circuit gas boiler is that the former is built primarily for heating, while the latter incorporates a flowing water heating system into its construction that not only heats the home but also supplies hot water.

The double-circuit boiler is a double appliance by construction. It supplies hot water through water heating, whereas a single-circuit boiler can only heat water when another boiler is connected to it.

These devices’ names reveal their primary distinction. In a single circuit, there is only one coolant circuit; in a dual circuit, there is a second source of water heating. Boilers with two circuits can have one or two heat exchangers at the same time. The first version has a switch that allows the gas supply to be turned on and off for heating. In the second scenario, water is heated by independent heat exchangers for both water supply and heating.

After purchasing a home, a gas project must be created in order to permit the installation of such equipment inside the home before purchasing a boiler. Next, make sure to research the differences between a single- and two-circuit gas boiler, speak with an expert, and determine whether a specific heating option is truly necessary.

A number of types are also distinguished for the two-circuit version. A heat exchanger, which consists of several bent tubes with plate elements, may be installed in it. Additionally, there is a bithermal heat exchanger that resembles a cell phone. Where there isn’t a lot of water hardness, the last model works better.

Advantages of both types

Boilers come in a variety of versions, each with a mix of advantages and disadvantages. They must be taken into account in order for you to decide wisely when installing a specific boiler model. Benefits of models with a single circuit:

1. They have an automatic safety system. It is possible to adjust the most acceptable mode of gas consumption and boiler operation.
2. On the basis of such boilers it is possible to create various heating systems with distribution to all rooms.
3. Presence of special sensors for climate control. They help to increase or decrease the gas supply and heating, depending on the ambient temperature.
4. Reliability and ease of operation.
5. Long service life.

However, keep in mind these benefits of a two-circuit boiler:

• It will cost less than a single-circuit boiler and a boiler at the same time. If you want to provide your home with hot water, the cost of this option is more favorable.
• Water is heated constantly and does not accumulate in the tank, as for example in a boiler. It heats exactly the amount you need, and there is no loss of heat due to cooling.
• The model has a small size and is conveniently placed in a modest room. Under certain conditions it is possible to install the device even in a non-residential area.

Everyone will, of course, select a boiler based on their own tastes, but it’s best to estimate the capacity in advance to avoid overspending on overly potent options.

This indicator is dependent on the number of occupants living in the house, the area of the heated premises, and the necessary constant temperature. Several experts advise purchasing a single-circuit boiler and a 200-liter storage tank to heat water liters in case you require a hot water supply. For water heating, someone suggests combining a gas column with a single-circuit boiler.

Disadvantages of both types of boilers

What works for one buyer may not be acceptable to another. Consequently, you must weigh the advantages and disadvantages of each boiler type before selecting the optimal one for your heating needs.

Cons of utilizing a boiler with a single circuit:

1. To heat water requires an additional device, which can be expensive and take up a lot of space. Very inconvenient in small houses.
2. If an additional appliance is used for heating, the single circuit boiler will continually consume gas to keep the water at the correct temperature. As a result, gas consumption will be higher, which will hit the consumer"s wallet.

The drawbacks of a device with two circuits:

• It is necessary to maintain a balance between water consumption and heating, otherwise unstable temperatures occur. If several taps are turned on at once, the hot water jet may not be satisfactory.
• When using water with a high degree of hardness, salt deposits can accumulate, which will lead to the deterioration of the device.
• Uneconomical consumption of water, because after switching on it will take several minutes to heat it up.

In conclusion, it is advised to compare the two appliances primarily based on the room’s floor area. For instance, it is preferable to purchase a two-circuit compact model for a small summer house, as it will occupy less space and be able to heat the area as well as the water.

Important: However, a single-circuit boiler and a large storage boiler are preferable if you live in a large cottage with multiple floors. This ensures that there is enough water and that the temperature of the water stays constant. You can read about the best boiler to select for heating a private residence at the provided link.

Hot water supply with a single-circuit boiler

As already mentioned, hot water supply can be organized and with a single-circuit boiler. For this purpose, an indirect heating boiler is connected to it. Water is usually used as a heat carrier, but special liquids with higher specific heat capacity and less corrosive activity, which do not form scale and do not freeze at subzero temperatures, are also used. The coolant heated in the boiler not only circulates through the heating system, but also passes through the heat exchanger built into the storage tank of the external boiler, heating the water in it. By the way, indirect heating boilers are also used in urban apartment buildings, only they do not work from an autonomous boiler, but from the centralized heating supply.

Device and principle of operation of single-circuit models

The basic idea behind how single-circuit boilers operate is that the boiler is connected to the heat generator (such as an ignited solid fuel, gas or diesel burner, TEN, etc.).д.) warms the heat exchanger, which is basically a circuit made of water. The coolant (usually water) in the heat exchanger cycles through the heating system either naturally or under force, providing heat for the home.

A straightforward condensing single-circuit gas boiler is designed.

Only with the use of extra equipment—such as a gas heater or an indirect boiler, which we will discuss later—can sanitary hot water be heated.

Types of two-circuit boilers

Boilers with a single heat exchanger for both circuits and boilers with two distinct heat exchangers are the two main types of two-circuit boilers.

Boiler with two circuits and a single heat exchanger

Compactness is the primary benefit of a single heat exchanger two-circuit boiler. A gas burner heats a single heat exchanger that receives water from both circuits (heating and hot water supply). The heat exchanger is segmented into insulated sections to prevent the mixing of water from various circuits. Similar to a single-circuit boiler, a special liquid can be used as a coolant in the heating circuit in place of water.

Boilers with bithermal and plate heat exchangers are separated from two-circuit boilers with a single common heat exchanger.

• The bithermal heat exchanger is a complex cellular construction with two non-communicating channel systems. Bithermal heat exchanger takes up little space and has a very high efficiency (up to 93.4%). The disadvantage of the design is that the water in different segments has different temperatures (that is why it is called bithermal). This leads to mechanical stresses, deformations and increased salt deposition inside the heat exchanger. Therefore, bithermal heat exchangers are better not to be used where the water has a high "hardness".
• Plate heat exchanger – a system of two independent circuits of curved tubes, united by metal plates. At the same capacity it has larger dimensions and slightly lower efficiency. Like the bithermal, the plate heat exchanger is subject to internal stresses, although to a lesser extent, but due to the simple configuration of the channels and their larger cross-sectional area, the deposition of salts occurs in it less intensively.

Boiler with two circuits and two heat exchangers

More area is needed for a two-circuit boiler with two independent heat exchangers than for a boiler of the same capacity with just one heat exchanger. It does, however, also have a lot of benefits. First off, independent heat exchangers have a somewhat longer service life because less scale settles in them. Second, you can avoid stopping the heating system while using hot water because both circuits function independently of one another and, in many models, each has its own burner.

A two-circuit boiler that has two separate heat exchangers is actually a gas heater and a heating boiler combined into one housing. However, a boiler of this kind is smaller than two independent appliances and eliminates the need for a chimney and a single gas supply pipe.

Device and peculiarities of boiler operation

These days, gas boilers can be single- or double-circuit, depending on how many circuits they have. Although they share similarities in appearance and structure, their functions and environments differ.

Consequently, one could argue that neither type of equipment is superior because they are both equally beneficial and efficient. So, making the correct decision is everything. Let’s now examine in more detail what makes a single-circuit gas boiler different from a two-circuit boiler.

Differences in the design of single- and double-circuit units

Most products that fall under either category of equipment share the same parts.

The following figures show the detailed device of a contemporary single-circuit wall-type boiler and the device scheme of its two-circuit "brother":

Both the name and the function of the two types of boilers are similar.

Thus, comparable components of single- and dual-circuit apparatus:

• cold water supply pipelines;
• gas burner;
• membrane tank;
• chimney.

The term "heat exchanger" even refers to the design element used in them to heat water.

If you sort it out, though, you’ll find that the heat exchanger single-circuit unit, as the name suggests, is just a pipe that efficiently transfers the heat released during the combustion of gas and water. This is the only similarity between the specified unit and other types of boilers.

One notable distinction between two-circuit boilers is that the former have all the components required for both hot water supply and building heating. As a result, there won’t be any further expenses for the acquisition of equipment, and they also let you save space.

Furthermore, because the heat exchanger in its two-circuit analog has a more complicated structural design, things are not as straightforward. Furthermore, these products are dual, bithermic, and classified into distinct subspecies.

In the first example, a pipe is incorporated into a product that is similar but has a bigger diameter. With the help of this feature, you can design two circuits: one for the hot water supply system and the other to transfer the heat of the heating liquid.

What makes up a dual heat exchanger is:

• pipes that provide heating water for heating;
• plates that transfer heat to the water supply fluid.

That is, the fact that two problems must be solved is the only reason why the heat exchangers in two-circuit boilers differ in terms of structural complexity.

However, the inclusion of a three-way valve in the double-circuit product’s design remains the most notable distinction between single-circuit and double-circuit products. whose job it is to reverse the flow of hot water.

As a result, when the valve is in its standard position, only the radiators receive coolant supply. Opening the hot water tap causes a complete transformation. Because the three-way valve shifts positions after receiving the proper signal. especially in the supply of hot water.

In this scenario, the coolant supply to the radiators is cut off, and the building will not be fully heated for the duration that hot water is used for household purposes.

In other words, the two-circuit boiler can only provide hot water in one of two modes due to its design. However, this feature shouldn’t be viewed as a flaw in the apparatus.

Comparative overview of gas boilers

The coolant used to heat buildings and rooms is heated by either of these two kinds of equipment. Additionally, single-circuit boilers have limited functionality in this area.

The only purpose of a single-circuit gas boiler is to heat the coolant that enters the heating system’s radiators. However, if you add an indirect heating boiler to it, it will be able to supply hot water just like its two-circuit counterpart.

In addition, their two-circuit equivalents are employed to supply hot water for any domestic chore. In other words, they enable one to wash dishes, take a shower, and carry out any other hygienic task.

In addition, we’ll compare single- and double-circuit boilers based on a variety of factors.

Comparison criteria	Single-circuit boiler	Two-circuit boiler
Type of installation	floor standing; wall mounted	floor; wall
Additional capital investment	if there is no need for DHW; if DHW is required, it is necessary to purchase a storage fan boiler	are absent if there are no more than 2 extraction points and they are located near the boiler
Economy	is switched on when the water temperature in the boiler cools down below the permissible temperature level	The heating circuit is switched on when the coolant cools below the permissible level; The DHW circuit is switched on every time the water is drawn
Compactness	when used in conjunction with boiler occupied area is actually doubled	more compact than single-circuit models; wall-mounted models are suitable for use in confined spaces
Convenience of use	when used together with a boiler hot water will be the same temperature at all points of extraction; the coolant in the heating system is supplied evenly	When the boiler capacity is insufficient and there are many water intake points, there may be overflows water and coolant temperatures, and sharp; when the taps are open, water is not supplied to the heating system

As can be seen, additional equipment will need to be purchased in order to arrange hot water supply when a single-circuit boiler is present. An indirect heating boiler is one example. Furthermore, this is an extra cost.

In addition, a boiler must be connected and installed correctly after purchase. We went into great detail in this article about how to operate such devices correctly as well as what to keep in mind.

Advantages and disadvantages of equipment

The features of durability, efficiency, and ease of use distinguish both types of gas boilers. Their appearance is also quite appealing.

Each type of gas boiler has been designed with the needs of various user categories in mind, as evidenced by the features and disadvantages of each design. Additionally, they give potential buyers the chance to learn about the distinctions between a single- and two-circuit gas boiler, assisting them in making the best decision.

Pros and cons of single-circuit units

These products can offer consistent heating for any size space, regardless of the floor area or distance from the heat exchanger.

Furthermore, single-circuit boilers:

• more reliable than their two-circuit counterparts, the design of which is more complex, which leads to a slightly higher number of breakdowns;
• easier to maintain, which is also due to the design features;
• cheaper.

One significant benefit is that single-circuit units can serve as a foundation for attaching additional devices. which will improve living comfort and increase their functionality.

Never forget that you will need to purchase a storage boiler if you need to provide hot water for the premises in addition to a single-circuit boiler. And this will result in a significant increase in expenses. Additionally, the equipment on the list will take up a lot of room, which can be problematic for small apartments.

The buildings’ hot water will be supplied by connecting storage boilers. Additionally, the water will always be supplied at a high temperature—something that two-circuit analogs can’t always accomplish.

There are no significant drawbacks to this kind of equipment when a hot water supply is not required. Otherwise, however, the lack of adaptability is immediately noticeable. which means that an additional electric heating device needs to be bought.

Its combined use with a single-circuit boiler therefore results in:

• high costs for purchase, installation, maintenance;
• limited volume of water for domestic needs – for joint use with single-circuit units are most often bought boilers, so there may be a question of rational water consumption, the volume of which depends on the capacity of the storage tank;
• greater load on the wiring.

The final drawback applies when there is outdated wiring in a home or apartment or when there is powerful electrical equipment being used in parallel. Therefore, it might be required to choose a cable with a larger cross-section and update the wiring.

It should be noted that a single two-circuit boiler requires substantially less space than a set of single-circuit boilers. Additionally, this can be a serious drawback if there isn’t much room.

Advantages and disadvantages of two-circuit boilers

Units of the aforementioned type that have certain restrictions but are nevertheless able to simultaneously supply hot water to two systems (heating and hot water supply). Furthermore, compared to their boiler counterparts, they occupy less space. Two-circuit boilers are therefore easier to operate.

The features of durability, efficiency, and ease of use distinguish both types of gas boilers. They also have a lovely appearance.

Furthermore, the manufacturers’ battle for market share has caused the price differential between the two types of units to gradually level out.

As a result, the price of a two-circuit boiler nowadays can marginally surpass the same indicator of a single-circuit product. That may also be seen as a benefit in certain circumstances.

When discussing the drawbacks of two-circuit boilers, the inability to instantly supply hot water at the same temperature at every location where water is consumed within the home or apartment is thought to be the most significant.

Thus, the quantity of water required at that moment is heated by their heat exchangers. In other words, no reserve is established. As a result, during use, the water’s temperature may fluctuate or differ from what is anticipated. This occurs, for instance, when the second tap is opened or closed and the pressure changes in the head.

The temperature of the water can vary between two points of water intake when using a two-circuit boiler; hot water can be delivered to the desired point with a delay, but not a significant delay. which causes inconvenience and extra expenses.

In terms of installation, two-circuit boiler installation is a more involved process, particularly in the design phase. Because you must adhere to the many guidelines provided by the manufacturer

Single-circuit heating boilers

The task of a unit with a single circuit is only to heat rooms, to create a comfortable temperature in them. To provide hot water supply, another equipment is connected to it – an indirect heating boiler. From the name it is clear that the circuit in the device is one, so the principle of its operation is quite simple. Thanks to the fuel entering the furnace chamber, the coolant circulating through the pipes inside the device is heated up. Its movement is provided either by a circulation pump (gas, electric equipment), or by the temperature difference (natural circulation in energy-independent boilers). To guarantee quality heating, the water must circulate in the circuit constantly.

To organize hot water supply to a single-circuit unit it is necessary to connect an additional circuit. As a rule, in this role is a boiler. Connection is not difficult, but there are disadvantages to such a "tandem". Connecting an additional circuit causes unstable operation of the boiler. The reason for this is the different amount of heat required to heat the water: more of it is consumed in the morning and in the evening. First, the boiler will have to be reconfigured, feeding a larger amount of fuel. After the period of maximum water intake is over, the device will start working again only for heating, which inevitably leads to overconsumption of fuel.

Components of single-circuit equipment

These kinds of structures are made up of:

• fan;
• gas block;
• Chimney;
• control unit;
• gas burner and heat exchanger combined with it;
• casing, control board with self-diagnostic sensors;
• thermostat, temperature sensor;
• three-way valve;
• circulation pump.

Electricity grid-powered appliances are not included in non-independent models. Despite their most basic design, these devices function well because they are meant to be used in places without power.

Varieties of construction

Floor-standing and wall-mounted single-circuit boilers are classified based on where they will be installed.

1. Floor standing units, installed either directly on the floor or on a stand. They are characterized by high weight, high power. Many models are equipped with the most efficient devices – cast iron heat exchangers, the payback for them – the greater weight of structures. There are boilers that allow you to create a cascade connection, but they are designed for buildings of large areas.
2. Wall constructions. These are compact units that are usually attached to load-bearing walls. Since the weight of such models is very limited, wall-mounted boilers are more often not characterized by high capacity.

The kind of combustion chamber used to classify single-circuit units is another factor. It could be closed or open.

1. Atmospheric – open. In this case, the air comes directly from the room, which must be equipped with an efficient ventilation system. Smoke extraction is provided by natural draught in the chimney.
2. Turbine – closed. In such models, the air intake is performed by a fan blowing air from the outside. The same device creates the pressure necessary for the exhaust of combustion products.

Single-circuit boiler models can perform additional tasks. These include the ability to program the mode of operation, have remote control capability, and include equipment in the "smart home" system, among other things.

Advantages, disadvantages of simple devices

Single-circuit equipment has benefits even though its single function can be viewed as a drawback.

1. Equipped with an automatic safety system. It allows you to choose the optimal mode for operation, and therefore can reduce fuel consumption.
2. Variability. Single-circuit boilers allow you to create completely different systems of heating distribution on the premises, which can significantly increase the service life of the unit.
3. The equipment of modern models includes sensors of air temperature outside the house. Depending on their readings, the fuel supply is regulated, and the temperature in the pipeline is lowered or raised.

The benefits that for many become crucial are simplicity, design dependability, high power and the lack of losses during heat transfer, ease of control, and unit adjustment. One more benefit of single-circuit models is their lower price if heating water for family needs is not necessary.

One significant drawback of these models is their restricted functionality. This renders the gadget inappropriate for homes lacking a hot water supply. Purchasing extra equipment, such as a water heater, is one solution, but it will come at a significant cost.

Two-circuit universal boilers

The presence of a second circuit (and heat exchanger) in the second equipment, which is intended for the configuration of the hot water supply system, is what distinguishes a two-circuit boiler from a single-circuit boiler. It is feasible to simultaneously arrange the water supply to two water intake points with powerful models. The boiler is as close to them as possible to avoid the water cooling down the route.

Circuits and heat exchangers

The transfer of some of the energy from the hot coolant leaving the main heat exchanger to the secondary plate heat exchanger ensures the additional function of heating cold water. Because this element heats water while it is flowing, there are limitations for users, particularly if there are a lot of them. The heating of the liquid gets worse with increasing water intake intensity. There are models where one of the circuits has a priority setting.

The problem of inefficient heat distribution between two circuits has been solved. For this purpose, bithermal, combined heat exchangers were created. These are coils made of coaxial type pipes. In the inner volume of them circulates hot water, the outer one is occupied by the coolant. Because of the simultaneous heating of liquids, inventors had a chance to get rid of the disadvantage of conventional units, to prevent losses of thermal energy. Such devices are maximally efficient, but not perfect, as they have another disadvantage. This is the rapid formation of lime scale, which is difficult, almost impossible to remove, and the replacement of the "super heat exchanger" will cost a large amount of money.

Two-circuit boilers come in two varieties: ones with a single heat exchanger (like bithermal boilers) and others with two conventional elements. The coolant used for heating purposes passes through the heat exchanger first. When hot water is required, the coolant supply is cut off and replaced with a cold liquid, which causes the machinery to begin heating up. Such a single-element system will be a little inconvenient during the winter.

Because they do not have this drawback, boilers with two heat exchangers are more widely used and in higher demand. They function with both "devices in the device" operating separately of one another. While the other heat exchanger heats the liquid required for the hot water supply, the first heats the water for the heating system. With the steel heating elements found in modern two-circuit boiler models, the coolant and cold water heat up quickly.

Pros and cons of two circuits

Apart from their primary benefit, two-circuit boilers possess multiple other advantages when compared to their less complex counterparts. These are the following:

• lower price of the equipment, if you compare it with the cost of a set – a single-circuit device and an indirect boiler;
• The absence of a storage tank, in which it is necessary to maintain a constant water temperature, this gives a chance to reduce heat losses, reduce costs;
• practicality – cost-effectiveness, efficiency, the ability to temporarily disconnect DHW.

For many owners, dual-circuit devices are the best option because of their power, compact design, and affordable cost. Cons: The hot water volume is limited, and the heating system’s temperature is entirely dependent on the amount of water users use.

Which boiler is better to choose?

Here is a comparison between a single- and two-circuit boiler to help you decide which is best for your house.

Particularly for bithermal applications, a two-circuit boiler with a single heat exchanger is a great option when it’s crucial to utilize every square centimeter of available space. In situations where this problem is not as serious, a two-circuit boiler with independent heat exchangers is preferable.

The cost of a single-circuit boiler in addition to the boiler is higher than the cost of a two-circuit boiler with similar parameters. In order to organize hot water supply, a single-circuit boiler must be connected to the boiler indirectly, which will require additional space. However, the indirect boiler, which is attached to a single-circuit boiler, has advantages over the flow water heater, which is a component of a two-circuit boiler, just like any other storage water heater.

While the temperature of the water from the flow heater can change, particularly if multiple consumers are turning on at once, the hot water from the boiler is independent of its flow rate. Just keep in mind that it will take some time for the boiler to reheat after the hot water runs out. As a result, it is essential to determine ahead of time what boiler volume will work best under particular circumstances for a continuous supply of hot water.

Two-circuit boiler – for a small country house

Therefore, the primary benefit of two-circuit boilers is their ability to save space; the primary drawback is the instability of the hot water temperature when multiple consumers are added at once. For a small country house, a two-circuit boiler will therefore be the best option.

Single-circuit boiler with a boiler – for a large cottage

Although a single-circuit boiler and the boiler that connects to it require more room, this type of design can reliably supply hot water to multiple water points. Thus, it is preferable to use a single-circuit boiler in conjunction with an indirect heating boiler in a large cottage or capital house where friends or relatives may drop by and hot water may be required in both the kitchen and the shower room at the same time, and where saving one or two square meters of space is not imperative.

Comparative table of characteristics and prices

Model	Method of installation	Capacity, kW	DHW capacity (35°C), l/min (boiler volume, l)	Cost, rub
Two-circuit gas
Lemax Premium-20N(B)	Floor	20	4,3	30 000
Baxi SLIM 2.230i 4E	Floor	22,1	9,3	110 000
Baxi ECO-4s 24F	Wall-mounted	24	9,8	36 000
Buderus Logamax U072-12K	Wall-mounted	12	6	28 000
Single circuit gas + boiler
Lemax Premium-16 + Kospel SWR – 100	Floor standing	16	100	23 000 + 14 000
Viessmann Vitopend 100-W A1HB001 + Drazice OKC 200 NTR	Wall-mounted	24	208	42 000 + 26 000
Baxi SLIM EF 1.31 + Baxi UBT 200	Floor-mounted	30,5	200	60 000 + 26 000
De Dietrich DTG X 30 N + Drazice OKC 200 NTR	Floor	30	208	88 000 + 26 000

Dimensions

Wall-mounted and floor-mounted units are divided into categories based on the type of installation. The equipment on wheels is equipped with a volumetric cast iron heat exchanger. They are larger and heavier than wall-mounted ones, but they last longer. They require more work to install as well. In terms of features, the floor-mounted model lacks sophisticated automatics and is simpler than the wall-mounted model.

Service life

The thickness and material of the heat exchanger have a major impact on the resource of gas equipment. The material thins annually as a result of oxidation-reduction processes, and this process continues until the material is completely sealed. Furthermore, the equipment will need to be replaced even if other, far less dependable components are in order. The longest service life is 12–17 years for heat exchangers made of reliable cast iron alloys; for copper and cast iron, it is 11–15 years.

Economy

Gas equipment’s economic parameters are directly influenced by:

• Heat exchanger material.
• Availability of quality components.
• country of manufacture.
• Regularity of scheduled inspections.
• Efficiency of the unit.

Condensing boilers rank first in terms of economy, followed by wall-mounted and floor-standing boilers in second and third place, respectively.

Heating area

Two-circuit devices are recommended for smaller country homes measuring between 100 and 120 m2. This is because of the minimal needs in the occupied area and DHW. A boiler and one circuit is the alternative. If you’re willing to invest an extra 15 to 30 tons.р. (roughly equivalent to the cost of a boiler) and give up 5 m2 of floor space for its installation, this combination will work best. particularly if the house has a large area and numerous intake points.

Convenience

A gas or flow water heater can also be utilized as a storage unit in addition to a boiler. When compared to a 2-circuit apparatus without a heat exchanger, any of them has a number of advantages. A substantial supply of DHW (ranging from 60 to 300 liters) is the first of these. One more thing: the temperature of the hot water is constant, independent of the quantity of intake points and does not decrease at high flow rates.

Additional functions

Weather-dependent automatics are occasionally installed in heat engineering devices. Thanks to its assistance, the room is kept at a comfortable temperature and substantial fuel savings are achieved as the equipment reacts automatically to changes in the outside weather.

Any boiler can have its equipment remotely reset or reconfigured by connecting a GSM module to it. The need (elderly parents or small children) occasionally materializes.

Criteria for a competent choice

1. Performance. The calculation is made after analyzing the area of the room and the possible heat loss.
2. Number of serviceable circuits. If it is necessary to heat the room and hot water supply, choose a two-circuit boiler with a pair of heat exchangers. If DHW is not needed, a single-circuit boiler is enough. In new two-circuit heaters there is a "Winter/Summer" mode.
3. Material from which the heat exchanger is made. For the primary circuit use steel or cast iron, and for the secondary copper and aluminum. From the material depends on the service life, heat conductivity and cost.
4. Automation. It is provided in the two-circuit turbo boiler. There are two types: standard and weather-dependent. New models have built-in remote control units. The model can be additionally equipped with remote notification. Gas consumption depends on the number of automation functions.

German companies manufacture the best models of gas boilers. French and Italian goods are ranked second in terms of popularity. Russia also started to provide affordable boilers that were competitive in the market.

The most dependable boilers from Vaillant Turbo TEC, Viessmann, and Vaillant Atmo TEC, in addition to those from Baxi. Neva Lux and Arderia models come in second and third, respectively. Korean products manufactured by Navien, Hydrosta, Daewoo, and Kiturami have poor build quality and dependability.

Requirements for installation

When installing atmospheric boilers, the strictest regulations are applied. Only agents of the gas company are allowed to install and connect equipment, after which a contract for additional equipment maintenance and inspection is signed. Every connecting unit needs to be expertly and incredibly hermetically sealed.

It is possible to install the turbo boiler on your own. However, keep in mind that even the smallest infraction will result in a drop in performance, and the manufacturer will refuse to provide warranty service.

What to pay attention to when buying a two-circuit boiler

When selecting a gas boiler, dependability and safety should be the primary considerations. Only boilers that are produced in factory conditions, have passed the control system, and come with a manufacturer’s warranty satisfy these requirements. As a result, the only products you should buy in stores should be certified ones rather than questionable creations from unidentified manufacturers.

The boiler should be chosen for more reasons than just its price and technical attributes. A high-quality maintenance service should be given for your heating appliance. It is crucial that your call is answered promptly, that replacement parts are available, and that heating equipment is repaired as soon as possible.

In order to prevent limescale buildup and frequent boiler breakdowns, a filter must be installed during heater installation in the flow heat exchanger used for hot water preparation. A coarse filter has to be installed as well to protect the heating coil.

What two-circuit wall-mounted boiler to choose?

The boiler connection scheme that is depicted above is highly traditional and does not encompass the range of these devices. Therefore, a closer examination of the primary selection criteria is required in order to make an informed decision regarding which model to use.

Boiler output and capacity

• The boiler must fully cope with its main task – to ensure the operation of an autonomous heating system. So, one of the basic selection criteria is its thermal capacity.

Experts determine an apartment or home’s overall heat demand by taking into account a variety of parameters, such as the size and shape of the rooms, the type of wall material, the building’s level of insulation, and the climate zone in which the residence is located. One reasonable way to simplify the process of determining the necessary boiler output is to use the standard of 10 m² of steamed room area per 1 kW. If the house (apartment) is adequately insulated and has an average ceiling height of no more than 2.5 to 3 meters, then this rule will be in effect.

It is obvious that the heater shouldn’t operate at maximum efficiency, so it is preferable to set aside a specific reserve, particularly if the insulated multi-story building is still uncertain. In addition, the boiler requires more electricity in order to heat the water. To put it briefly, adding an additional 30 ÷ 35% to the obtained value won’t be incorrect.

Most contemporary two-circuit boilers have a sufficiently broad capacity range. The technical documentation typically provides the value’s minimum and maximum values. Useful heat output, for instance, is 9.3 ÷ 14 kW.

• The second component of the problem is the performance of the device to heat water for domestic needs. If there is no boiler, then heating will be carried out by a flow scheme, and the parameter of choice depends on the number of water points that can work simultaneously. It is clear that the more liters per minute can heat the boiler, the better.

Technical documentation for two-circuit boilers typically lists multiple capacity values along with varying values of the temperature differential at the inlet and outlet. Function typically at Δt° = 25 and 35 degrees. It is precisely the increase in its value over the input value, not the temperature of the water at the outlet. For instance, during the summer, the water supply system may have 15° C of water, and at Δt° = 25°, the taps will receive 40°, which is perfectly fine for a shower.

Approximately 10 ÷ 11 l/min at Δt° = 25 °C and 7 ÷ 8 l/min at Δt° = 35 °C are regarded as very good performance in theory.

Only when the water pressure in the water supply and the gas pressure in the mains match the manufacturer’s specifications will all these features be functional. This also warrants careful consideration.

Type and number of heat exchangers

Boilers can vary greatly in how they heat water for domestic hot water. Thus, there are two primary types of these devices: bithermal and with a secondary heat exchanger. Every kind has unique characteristics.

The boiler’s primary heat exchanger, which handles heating—the operation that uses the most energy—is always situated above the gas burners. Additionally, heat from the heated coolant can be transferred through a secondary heat exchanger, an additional device, to heat the water.

Type of combustion products removal system

There are two sizable subgroups of boilers: those with an open combustion chamber and those with a closed one. As a result, the systems that supply the air required for gas combustion and release the combustion products into the atmosphere set them apart.

Controls, automatics, protection levels

The boiler needs to be relatively simple to operate, have intuitive controls, have all the features needed to maximize efficiency, and have multiple levels of emergency protection.

Leading manufacturers are always enhancing their models, which fuels brand competition and results in an endless stream of new innovations. Therefore, the following features can be added to contemporary boilers:

• Flame modulation in heating and water heating modes. The flame level is electronically regulated, ensuring smooth starts, which is especially important for models with flow heating of DHW water. The automation independently selects the height of the flame tongues depending on the set temperature and the specific current water flow rate.

In certain models, the final five degrees of heating system temperature are achieved at a lower combustion intensity. This makes it possible to improve the device’s operation, lower the number of starts, and ultimately lengthen the equipment’s service life.

• The same objectives are pursued by the system of smooth electronic ignition, when after the appearance of a minimum flame on the burners it gradually increases to a given intensity of combustion for 30 – 40 seconds.

This option is not applicable when the boiler is used as a water heater; in this case, the rate at which the water heats to a specific level is crucial.

• Weather-dependent boiler automation. This innovation, with the installation of an external outdoor sensor, allows the equipment to monitor the external temperature level and make adjustments to maintain an optimal microclimate in the apartment.

This kind of equipment is more sophisticated and includes an automatic self-adaptation feature. Electronics analyzes and makes adjustments to the boiler to maximize comfort and save a substantial amount of gas in addition to comparing the graphs showing changes in both internal and external temperatures.

• Pump post-circulation. A useful function, which, when installed room thermostat, allows you to significantly reduce energy consumption. Once the heating system has reached the required heating temperature, the boiler is switched off and the pump continues to run for another three minutes. Both the boiler and the pump can be started at the same time when the boiler needs to be restarted.
• Naturally, all modern boilers with electronic control allow you to accurately set the temperature in the heating circuit and in the DHW. In addition, some models have two switchable ranges in heating mode – for conventional radiators and for underfloor heating.
• The electronics allows you to program the boiler operation for a certain period of time, with the entry of programs into memory for repeated use.
• Any gas equipment has several degrees of protection – in case of insufficient draught, in case of heater fading out, in case of absence or insufficient water pressure in the circuits, etc.п. In addition, modern models are also equipped with other safety functions. So, if the temperature in the circuits falls to +5 degrees, the boiler will start independently to bring the level of heating medium and water to a safe value to avoid freezing. In addition, some control systems also monitor the state of the elements of the boiler. If the device has not been used for more than a day, the processor for a short time will turn on the pump or switch back and forth the position of the three-way valve. This avoids blocking or "sticking" of these units, prolongs their operational life.

Control panels can be electromechanical, touch, or push-button operated. They can also have digital or arrow indicators showing the system’s pressure and temperature.

Dimensions, "appearance", manufacturing company

The boiler’s dimensions should be a mandatory evaluation criterion; they must match the space where the installation is intended. This considers the position of the gas mains as well as the potential for installing a coaxial system or connecting to a chimney. There are certain limitations in these cases, such as those pertaining to the coaxial pipe’s length, which must be made clear in the product passport.

Purchasing a boiler with a built-in boiler may make sense if the installation location is large enough. Not only is the boiler’s size larger, but it also offers a significantly higher level of operation convenience.

For many owners, an important selection criterion is the design of the boiler. It is difficult to give advice here – the main thing is that the device does not spoil the interior. Most of the boilers have a matte white coloring, which fits perfectly into any style.

You should always choose reputable brands over other options, regardless of how much you like the model that is being offered for sale. Prominent manufacturers provide strong warranties for their products, which is crucial because the boiler can be considered an expensive purchase.

European businesses "Viessmann," "Beretta," "Baxi," "Vaillant," and "Bosch" are renowned for their "unblemished reputation" and rightfully so. reputable companies such as "Protherm," "Buderus," "Ariston," and others. The Korean companies "Navien," "Daewoo," "Celtic," and "Kiturami" produce equipment with modern electronics that can sometimes outperform that of European manufacturers, so it is quite possible to trust their products.

How to choose a boiler of appropriate capacity

If the choice in favor of a single- or two-circuit boiler has already been made, it is necessary to select a boiler of appropriate performance. In order to ensure that the air temperature in the rooms was comfortable and the temperature of hot water about 50 degrees Celsius you can make a simple calculation of the power of the installed boiler. For this purpose, the area of all heated rooms is summed up and divided by 10. This is the approximate heating load obtained. Increasing it by about 15-20%, we have the total output of the boiler, taking into account hot water supply. However, as professionals advise, the boiler should be purchased with a slightly higher capacity than the calculated one. The whole point is that over time the performance of the equipment falls, the heat transfer from the fuel to the heat carrier decreases, due to contamination of heating surfaces. In addition, when selecting equipment should take into account the value of heat losses from pipelines, possible voltage fluctuations.

Classification of two-circuit mounted gas boilers

Let us now examine the various types of gas boilers that are mounted on two circuits; these units are categorized based on three indicators:

• the principle of utilization of combustion products – convection and condensation;
• design of heat exchangers – separate and bitermic;
• the design of the combustion chamber and the discharge of its products – open and closed.

In the subsections that follow, let’s examine each one in isolation. You can read our article to learn how to select a solid fuel boiler for heating a private residence.

Convection and condensing gas boilers

Gas boilers are classified into two types based on the principle of combustion product utilization: convection boilers and condensing boilers. Let’s examine their distinctions, benefits, and drawbacks.

The "classic" and most widely used type of these boilers is the convection gas boiler. The energy released during the burning of the fuel, which is gas, is carried to the heat exchanger where it is already transferred to the water that is flowing through the circuits along with hot air flows upward. After that, the chimney is used to remove all combustion products. These devices have the advantages of affordability and ease of use. The underutilization of the energy produced by fuel combustion is the drawback. You can view our article to learn how to install convector heaters.

Boiler by convection with an open chamber

Condensing gas boiler uses a different, more efficient principle of operation. When burning gas is formed water vapor, which carries some (and quite a significant) part of the thermal energy, which must be "caught". For this purpose, the air streams coming from the burner pass through the primary heat exchanger and are cooled to a temperature of +56°C, which is the dew point. Then they fall into the chamber, where the economizer – secondary heat exchanger is located. This is where the vapors formed during gas combustion condense. During this process, the vapors give their thermal energy to the circuits through which the water used for heating and household needs is circulated. The condensate then accumulates in a special tank and from there it is discharged into the sewerage system.

Vital! The liquid from the heating system return flow passes through the economizer first before reaching the gas boiler. There, the coolant is heated for the first time by the energy released during the condensation of water vapor. The liquid undergoes a second temperature rise once it enters the primary heat exchanger, this time due to the well-known convection. The liquid is then directed into the supply line of the heating system using a pump.

Diagram showing how a condensing boiler with two heat exchangers works

Diagrammatic representation of a two-circuit condensing gas boiler apparatus

Condensing gas boilers have the benefit of a high efficiency factor of 90–95% (convection devices have an efficiency of 80–85%). However, these products also come with a high price tag and a very intricate design. To drain the liquid from the economizer chamber, you will also need to connect one additional main line to the condensing gas boiler. Please read our article to learn how to install wurdofuel boilers.

Two-circuit boilers with separate heat exchangers

These devices employ two heat exchangers. Water for the heating system is heated in one of them, referred to as primary. symbolizes a coil that is connected to pipes so that liquid from radiators can be supplied and drained. Numerous metal plates are positioned in between the coils of the primary heat exchanger; these plates expand the heating area and boost the gas boiler’s efficiency.

Additionally, a secondary plate-type heat exchanger is used to prepare hot water for household needs. It is smaller in comparison to the device mentioned above and has two independent circuits rather than just one. Water is circulated for household needs in the first, and for the heating system in the second.

The device and heat exchanger of DHW plates

There are two ways to operate a wall-mounted, two-circuit gas boiler with independent heat exchangers:

• heating mode;
• hot water supply mode (or abbreviated as DHW).

A three-way valve links the primary heat exchanger’s inlet and the heating system’s "return" in the first scenario. The coolant from the secondary product circuit’s outlet is obstructed. The primary heat exchanger’s water is heated to the appropriate temperature by a burner and igniter burning fuel. Water is subsequently directed by the circulation pump to the convector, radiators, and heating system.

When turning the hot water tap in the shower, bath or washbasin, the heating boiler switches to the DHW mode. In this case, the connection between the primary heat exchanger and the heating system is cut off, circulation in which stops for some time. As in the previous mode, due to the combustion of gas in the primary heat exchanger heats up the liquid. But at the same time it rushes not to the radiators, but to the secondary product. There, the heat transfer medium, previously intended for the heating system, transfers its energy to the water, which is then directed to the DHW line – in the shower or sink to the end user. As soon as one of the occupants stops using them – the boiler returns to the first mode of operation.

The two-circuit boiler’s basic working principle

Crucial! Since people use the sink, shower, and bath for relatively short periods of time, stopping the coolant circulation in the heating system when the boiler goes into the DHW mode does not significantly lower the temperature in the heated house.

Devices with independent heat exchangers, whose working principle was previously explained, offer the following benefits.

1. Large cross-section of tubes in the primary and secondary heat exchangers – they work longer, they are less likely to get clogged.
2. High repairability of elements of the gas boiler – to repair individual heat exchangers in case of breakdown is quite possible.
3. Comfort and safety for residents – hot water is heated to a lower temperature than the coolant in the heating system, so the probability of getting a burn when turning the tap in the shower or sink is minimized.
4. Since the water for DHW or the liquid for the heating system does not stagnate in the heat exchangers during heating, the scale on their tubes builds up at a relatively low rate.

However, it should be acknowledged that, even with their relatively straightforward designs, two heat exchangers cost more than one. Consequently, this has an impact on a two-circuit gas boiler’s overall cost. Furthermore, as stated in the operation modes, devices featuring a separate heat exchanger are large and have a vulnerable point in the form of a three-way valve.

Variants of draught equipment

Fuel is burned and flue gases are produced while the unit operates. It takes a forced or natural draught to get them out of the living area. It will guarantee that all combustion products and released hazardous materials are promptly removed from the apartment or home.

Modules with natural draught

Simple in design, naturally draft-operating boilers draw the air required for optimal combustion from the room in which they are housed. A certain amount of steam and different chemicals are released during vigorous operation. A chimney that is angled vertically releases emissions.

Natural draft units’ primary benefits are their affordable price, energy independence, and lack of noise pollution while in use.

Naturally draughty appliances are generally good and convenient, but their performance is greatly diminished when the gas pipeline pressure drops. Simultaneously, when the fire at lower pressure level is put out or moves inside the burner device, there is a greater chance of rapid burner burnout.

Inequitable pressure within the primary networks leads to a significant fuel overuse, resulting in higher utility bills.

Appliances with forced draught

Supercharged or fan-assisted boilers are other terms for forced-draught boilers. They draw their air from the street instead of the room in which they are situated. The modules feature sealed combustion chambers, and a strong fan built into the system allows the exhaust to be released through the coaxial horizontal outlet.

Two pipe elements of varying diameters are inserted into one another to form coaxial venting. Combustion products exit the room through the smaller pipe, and fresh air from the street enters the room through the space between the small and large pipes. This air is essential to the boiler’s proper operation.

Forced-draught products are simple to install, don’t take up any space, don’t "eat" oxygen in living rooms, function steadily and clearly in central main networks even at lower gas pressure, and don’t require the installation of an additional vertical chimney.

They are held accountable for the fan elements’ noisy operation, increased expense, and reliance on the power source.

Boiler manufacturers – what model is better?

It’s simple to become confused with the range of brands that offer their goods. How to select a boiler and avoid making a mistake in your selection. These days, equipment from multiple nations is primarily offered on the market for heat and power products. Germany, Italy, Korea, and Russia are these. Every boiler varies slightly in terms of the technical aspects of the job and noticeably in terms of price. boilers for heating made in Germany.

From the best side, Bush boilers have a long history of success. They are always refining their design. Automation and safety features that control fuel supply to the burner and activate in an emergency are built into the boiler. All heat exchangers are made of copper and are coated with a special composition to prevent corrosion, which improves heat removal during boiler operation. A boiler of this type is expected to last for 20 years.

Italian heating boilers

Boilers of Italian firms are also characterized by good build quality. One of the most famous Italian brands – Beretta, produces high capacity boilers. In the model range you can pick up heating equipment with capacity up to 24kW. It can be as single-circuit, double-circuit boilers, boilers with built-in and freestanding boiler. A distinctive feature of Beretta equipment is that it can operate at very low outdoor temperatures.
The firm Baxi on the market of heating equipment for several years already. During this time, specialists are constantly developing and implementing new solutions. In the fifth generation boilers installed atmospheric burner, which works almost silently. Baxi equipment is represented by a wide range of models with capacity from 10 to 80 kW. Boilers have a relatively small size and high efficiency – up to 90%.

Korean heating boilers

Korean boilers blend dependability with contemporary technology. They have mechanisms in place to guard against voltage drops, increases in collector pressure, and temperature rise. An integrated natural gas leak detector is another feature of the boiler. The boiler automation will turn off the gas supply to the burner device if it is detected. Boiler manufacturers include the company Navien in the lead position. It manufactures boilers with varying numbers of circuits and fuel types. The apparatus has burner components that function even when natural gas pressure is low. Furthermore, a built-in voltage stabilizer in the boiler guards against overloads.

Olympia is a company that specializes in producing weather regulation-equipped two-circuit boilers. You can select a boiler for any area’s premises thanks to this brand’s ample capacity range of models. The most recent automatic systems, which enable you to easily control equipment operation and even guard against system freezing, are included with all boiler models. boilers for homes.

Danko, a manufacturer of boiler equipment, consistently gets positive feedback from experts and users. If you have permission, you can easily select a boiler from the company’s selection of models, which range in power from 7 to 15 kW, to heat a small country house or apartment. The boiler unit has an efficient micro-flare burner, a steel heat exchanger, and a gas filter.

JSC "Borinskoye" Ishma BSC is another company that manufactures boiler equipment that is competitive. One characteristic that sets these boilers apart is the integrated circulation pump. You can use the boiler with or without a functional pump. In the event that the supply of electric energy is frequently interrupted, this is very practical.

Nuances of installation of heating installations

A chimney must be installed if the boiler has an open combustion chamber. Installing gas-fired equipment requires a project. You can designate certain points that will aid in the boiler’s more accurate operation if you have some flexibility in where to fix it.

Mounting flow heaters closer to the location of the water intake is preferable.

The distance between the heater and the valve where the water is frequently drawn should be kept to a minimum if there are two taps for the coolant return.

Structure and main differences

Three primary modules make up a gas boiler: the burner, heat exchanger, and control automatics. The combustion chamber houses the burner, and above it is a heat exchanger that heats the heating medium. Automation is used to control the entire process. It modifies the equipment’s modes of operation and offers safety.

Closed combustion chamber boiler (turbine)

Material of heat exchangers

The material the heat exchanger is made of may also have an impact on the choice of two-circuit gas boiler. It might be:

• Stainless steel. Not a bad option in terms of durability, but it has a fairly low heat output, which reduces the efficiency of the boiler. Nevertheless, the price of such a heat exchanger is high.
• Galvanized steel. This is the cheapest type of heat exchanger, but also the most short-lived one.
• Copper. Excellent option in terms of heat transfer (boilers have high efficiency) and durability, but the price is high. But this scares few people – outweighs the opportunity to pay less for gas in operation. It is for this reason that most good two-circuit gas boilers are equipped with a copper heat exchanger.
  This is what the primary heat exchanger looks like in gas wall mounted boilers

It is not too difficult to select a two-circuit gas boiler based on this parameter. It appears that copper is the best choice. High chemical activity and a low melting point are drawbacks, but they have long since figured out ways to make up for them. Overheating is prevented by the boiler automation. Using chemically neutral materials in the heating system, such as polymer pipes made of polypropylene or cross-linked polyethylene, neutralizes chemical activity.

Types of burners for gas boilers

A atmosphere gas burner is a feature of wall-mounted two-circuit gas boilers. They differ based on the flame control technique used:

• Single-stage. The burner either burns or not. No intermediate positions. To maintain the required heating mode, the burner is ignited and then extinguished. Not the best algorithm of operation.
• Two-stage. There are two modes of operation – at 100% capacity and at 50-60%. Automatics itself regulates the necessary power. Such burners are more economical, allow you to maintain the temperature more accurately. By reducing the number of on/off switches.
  Two-circuit gas boiler with modulating burner is the most economical
• Modulating. The most expensive type of burners, but also the most economical. Controlled by automation, the power is set such that is necessary at a given time from 10% to 100%. A two-circuit gas boiler with such a burner has a minimum of on/off cycles, which has a positive effect on durability. In addition, fuel consumption is 10-15% less under equal conditions.

Modulating burners is the best option, if we are talking about that. They make it possible to precisely heat water to the required temperatures as well as maintain the heating temperature. A modulating burner is a must for any affordable two-circuit gas boiler that you choose.

Method of installation

Gas boilers are installed in a floor or wall mounted configuration. Wall-mounted: tiny, kitchen cabinet-sized units that are wall mounted. They can be installed in the kitchen or another appropriate space; they don’t need the equipment of a separate room. A wall-mounted gas boiler has a maximum output of 30-35 kW. Typically, this is sufficient to heat spaces that are between 250 and 350 square meters in total. м.

Floor gas boilers are heavier, bigger, and more powerful than other boilers. While some models are small enough to fit in the living room, others need a separate space called the boiler room. Each manufacturer specifies installation requirements differently, but they typically include the room’s volume, ventilation, and the distance between the boiler’s top and the ceiling.

Wall-mounted gas boilers weigh more and are bigger, but this is because their output is higher.

Gas boiler installation, regardless of type, requires a certified project. A gas metre is a requirement of the scheme; in the event that one is not available, one must be bought. A business that has been granted a license to perform this kind of work must handle connection work. The boiler will only be permitted to operate under these circumstances.

Selecting a two-circuit gas boiler based on installation technique is simple. A wall-mounted model is typically chosen if there is sufficient power; if not, a floor-mounted one is.

Type of combustion chamber

The combustion chamber contains the gas burner. It comes in two varieties: forced (with a turbine) and open (atmospheric). Installing a two-circuit gas boiler with an open combustion chamber is restricted to well-ventilated rooms. When the appliance is in use, the room’s oxygen is extracted to provide the necessary combustion, and the combustion products are released into a chimney that has a strong draft. Because of this, having a reliable air supply and an efficient exhaust duct are crucial.

Both an open and closed combustion chamber are included with gas boilers.

The presence of a coaxial chimney, or pipe within a pipe, complete with a fan at the chamber’s outlet distinguishes gas boilers with a closed combustion chamber. If possible, lead the chimney in the wall next to the boiler to the street. A turbine fan ensures that the combustion products in the second pipe, which is used for air intake from the street, move freely.

Which combustion chamber is better? Boiler with a closed combustion chamber works more stably – the air goes directly into the combustion zone. But there is a disadvantage: in a side wind, the air flow can be so strong that it will blow out the burner, the boiler will shut down. The second disadvantage of such a solution – freezing and formation of ice in winter time. Well, and the third disadvantage – such a boiler works only in the presence of electricity – without a turbine, it shuts down. Well and another small minus – the turbine is not silent. It"s almost inaudible, but that"s exactly "almost". Apparently for these reasons, if there is a possibility (serviceable ventilation duct), put boilers with an open combustion chamber. After all, it is much easier to ensure a constant air supply.

Boiler capacity

Determining the necessary capacity is one of the most important factors when selecting a heating boiler. If you take full responsibility for the situation, you should figure out how much heat escapes from each room in an apartment or from the building overall if the boiler is being used to heat a private residence. The computation considers the type and thickness of the walls, the location of windows and doors, the amount of insulation they provide, whether there are any unheated rooms upstairs or downstairs, and the kind and material of the roof. Numerous other factors as well as geographic location are taken into consideration.

If you’d like, you can order such a calculation from a specialized organization (like GorGaz or the design office), handle it on your own, or choose the easy route and calculate using average norms.

The norm was determined based on the outcomes of all computations, and it states that 1 kW of heating power is needed to heat 10 square meters. This standard is appropriate for spaces with 2.5-meter ceilings and walls with a moderate level of thermal insulation. If this describes your room, divide the total area that needs to be heated by ten. The necessary boiler output is obtained. Afterwards, based on the actual circumstances, you can modify the resultant figure by making increases or decreases. In the following situations, increasing the heating boiler’s capacity is recommended:

• The walls are made of material with high thermal conductivity and are not insulated. Brick, concrete fall into this category exactly, the rest – according to circumstances. If you choose a boiler for an apartment, add power should be added if the apartment is corner. For "internal" heat losses through them are not so terrible.
• Windows have a large area and do not provide air tightness (old wooden frames).
• If the ceilings in the room are higher than 2.7 meters.
• If the attic in a private house is unheated and poorly insulated.
• If the apartment is on the first or last floor.

If the floor, walls, and roof are all well-insulated and have energy-efficient double-glazed windows installed, then the computed power should be reduced. The required boiler output will be represented by the resulting figure. Make sure the maximum horsepower rating of the unit is not less than your number when looking for the appropriate model.

Automation

Gas boiler automation is required because it provides safety and allows for mode switching. Three primary parameters are continuously observed:

• presence of draught in the chimney;
• gas pressure;
• flame control.

These are the crucial areas that only require management. The boiler will not operate if any of these parameters are out of the ordinary. There’s also a long list of extra functions available:

• Maintaining a stable temperature. There are two types of automatics: one controls the temperature of the coolant, the second controls the temperature of the air in the room. More comfortable conditions are created with air control – the weather changes, but regardless of this, the room is maintained in the set mode.
  This is the remote control from which all parameters are set
• Post-circulation mode. After the burner is switched off, the heat exchanger has a very high temperature. If the circulation pump is switched off immediately, the water in the heat exchanger can boil, which will lead to its failure. To avoid such a situation, the pump still drives the coolant for some time and turns off only when the temperature becomes acceptable.
• anti-freeze. If a two-circuit gas boiler is installed in a summer house, where you live only periodically, you can set the economy mode. The boiler will maintain a stable temperature of +5°C. The same function can be used for the time of departure.
• Summer mode. In summer the heating is not switched on, the boiler works only for water heating. In order that the system at this time did not stagnate, to avoid clogging elements, automation once a day for some time includes circulation of the coolant.

These are the common, yet distinct features: the ability to link and manage solar panels and underfloor heating systems. Automation that depends on the weather exists. In this instance, the street has been equipped with remote sensors. Their data indicates that the boiler’s operation has been fixed.

Ferroli Diva gas boiler control panel

Every one of these features is integrated into the microprocessor, which handles everything. The sole option available to the average user of all automatics is a remote thermostat, which can be placed in any room and adjusted in accordance with its indications (an additional option). Basically, there is only one small panel that is used for all communication with the boiler and its automation. The screen shows all the information that is required. You can also adjust the temperature and switch between modes using the buttons.

Other parameters

It happens that the price of a gas boiler, the principle of operation of this equipment does not play a decisive role for the consumer. If he pays more attention to the convenience of using hot water or consumes it in large quantities, then you should consider buying boiler equipment, in the design of which there is a built-in or external storage boiler. Such models have many advantages of boilers that use the flow method for heating hot water.
Even if there is no water left in the boiler, it will continue to operate as before. Also, a two-circuit boiler with a boiler is an attractive option and because it can work stably, regardless of what pressure is created in the water mains.

Rating of the best models

Numerous companies manufacture boilers that are energy-efficient. stand out from Russian. It provides units with different modifications.

The Lemax Classic-12,5 V floor standing gas boiler is the item with the best price-quality ratio. It has a 12.5 kW capacity. This indication is sufficient to heat a large 125 square meter home.м. Due to the boiler’s small weight and dimensions, finding a suitable location for it is not difficult. The appliance is as strong as possible for this material because it is fitted with a cast steel heat exchanger and has no seams.

Bestselling items under the Slovakian brand. The Protherm Bear 20 TLO boiler is regarded as having good efficiency. The cast iron heat exchanger in this appliance contributes to its weight. The model’s advantages include high efficiency (at 90%) and 18 kW of power. In actuality, the unit can heat a space up to 240 square meters (assuming the house is constructed with materials that minimize heat loss).

The Italian brand Baxi’s products have shown their worth. Popular model SLIM EF 1.22 has a high power output of 22 kW, which is sufficient to heat a 230–240 square kilometer home. Its efficiency, at 88%, is less than that of the models mentioned. Not every company considers this factor when releasing products, but this one has an attractive design and automatic devices that offer a high level of safety during operation.

Additionally, the Italian brand Beretta sells energy-efficient models. The primary benefit is the heat exchanger’s cast iron alloy construction, which adds longevity and durability to the apparatus. Silent operation and smooth ignition are features, which is crucial if the boiler is placed in a space where people are frequently present. The appliance has an 18 kW capacity and can heat a sizable area. With 93% efficiency, the gas consumption is relatively low.

Even though the aforementioned models have excellent construction and well-thought-out design, energy-independent boilers have certain inherent drawbacks, such as a thermocouple that fails relatively quickly—after 10 to 12 years of operation. Purchasing a spare is not difficult, but installing the part in a service center is preferable to doing it yourself.

Making the right decision between a dual-circuit and single-circuit gas boiler is essential for effectively heating your house. Dual-circuit boilers provide flexibility and possibly lower energy costs because they have separate circuits for hot water and heating. Conversely, single-circuit boilers use a single system to heat the hot water and the radiators. They might be less effective for homes with high hot water demand, despite being easier to use and frequently less expensive up front. The needs of your home, your financial situation, and the amount of available space will all influence your decision. Make the best choice for the insulation and heating of your home by taking into account variables such as hot water usage, installation space availability, and long-term energy efficiency.

Rating of TOP wall-mounted single-circuit boilers

Let’s look at the most widely used wall-mounted single-circuit boiler models:

MORA-TOP Meteor Plus PK24SK

With a power of 24 kW, the unit can serve an area of 240 square kilometers. The boiler is equipped with an electronic control system and multiple stages of protection against external interference or malfunctions during operation.

• THE EFFICIENCY IS 90 %;
• coolant temperature (max) – 80°;
• pressure to the heating circuit – 3 bar;
• gas consumption – 2.6 m3/hour;
• dimensions – 400x750x380 mm;
• weight – 27.5 kg.

The most popular models are those with this capacity because they almost perfectly suit the requirements of medium-sized private homes.

BAXI ECO Four 1.14 F

Gas boiler with convection, Italian. With its 14 kW of power, the unit is appropriate for rooms up to 140 square meters. м.

These could be tiny homes, offices, or apartments. Because of its closed combustion chamber, the unit can be placed in the kitchen.

Think about its attributes:

• EFFICIENCY – 92,5 %;
• heating medium temperature (max) – 85°;
• pressure to the heating circuit – 3 bar;
• gas consumption – 1.7 m3/hour;
• dimensions – 400x730x299 mm;
• weight – 31 kg.

Although the quality of Italian heating technology is well known, the costs are relatively high.

Viessmann Vitopend 100-W A1HB001

German appliance quality has long served as a standard for other manufacturers. The Boiler Vitopend 100-W A1HB001 validates the current viewpoint.

Its 24 kW capacity is the most sought-after amount for heating a 240 square meter home. м. It is feasible to install a turbine burner in the kitchen or other interior rooms of the house because they do not disperse smoke odors.

• EFFICIENCY – 91 %;
• Heating medium temperature (max) – 80°;
• pressure in the heating circuit – 3 bar;
• gas flow rate – 2.77 m3/hour;
• dimensions – 400x725x340 mm;
• weight – 31 kg.

If you want to use the unit as a liquefied gas supply, you’ll need to adjust the nozzle set and some settings.

Buderus Logamax U072-24

Superior heating boiler from a reputable German producer.

Being a "daughter" of the Bosh concern, the company aptly attests to the caliber and competencies of the unit. The heated area is 240 square meters, and the power is 24 kW.

• EFFICIENCY – 92 %;
• heating medium temperature (max) – 82°;
• pressure to the heating circuit – 3 bar;
• gas consumption – 2.8 m3/hour;
• dimensions – 400x700x299 mm;
• weight – 31 kg.

The device has a copper heat exchanger in the form of a coil. This improves heat transfer and strengthens and stabilizes the boiler’s operation.

Protherm Panther 25 KTO

This model has been modified twice, in 2010 and 2015.

They are not very different from one another. A few flaws have been fixed and the capacity has been marginally increased in the more recent design. With its 25 kW, homes up to 250 square feet can be heated.

• EFFICIENCY – 92,8 %;
• coolant temperature (max) – 85°;
• The pressure in the heating circuit is 3 bar;
• gas flow rate – 2.8 m3/hour;
• dimensions – 440x800x338 mm;
• weight – 41 kg.

Selecting between a dual-circuit and single-circuit gas boiler for home heating can be a critical choice. Making the best decision for your household requires an awareness of the differences between each option and its advantages and considerations.

A combi boiler, sometimes referred to as a dual-circuit gas boiler, is made to supply hot water for taps as well as central heating from a single unit. For smaller homes or properties with limited installation space, this can be a space-saving solution. You can have hot water on demand with a combi boiler, which does away with the need for a separate hot water cylinder.

A single-circuit gas boiler, on the other hand, is only used for central heating. It does not directly heat hot water for taps; instead, it heats water and circulates it through radiators or underfloor heating systems. In larger homes with an existing dedicated hot water cylinder, this kind of boiler is frequently chosen.

The two types of boilers differ primarily in how they deliver hot water. While a single-circuit boiler might need a separate hot water cylinder, which could take up extra space and cause delays in receiving hot water, a combi boiler can provide instantaneous hot water.

A dual-circuit or single-circuit gas boiler depends on how much hot water your household uses on a regular basis, how big your property is, and how much space you need. A combi boiler can be a better option if space-saving features and convenience are important to you. However, a single-circuit boiler with a separate hot water cylinder might be more appropriate if your home is larger and your hot water needs are higher.

In the end, the best option will rely on your unique requirements and preferences. Speaking with a licensed heating engineer can assist you in weighing your options and coming to a decision that will guarantee your home has an effective hot water and heating system.

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