How to choose a gas wall-mounted two-circuit boiler

Selecting the best gas wall-mounted two-circuit boiler is essential if you want to heat and insulate your house effectively. Choosing the one that best meets your needs can be overwhelming with the abundance of options available on the market. To help you make an informed choice, we’ll break down the important aspects to take into account when choosing a boiler in this guide.

It’s crucial to determine your home’s size and heating needs first and foremost. Since gas wall-mounted boilers come in a range of sizes and capacities, knowing how much heat your space requires will help you make a more informed decision. To choose the right boiler size, take into account elements like the number of rooms, the degree of insulation, and the local climate.

Next, think about the boilers you are considering in terms of their efficiency ratings. Efficiency is essential for lowering your heating costs as well as your energy consumption. High Annual Fuel Utilization Efficiency (AFUE) ratings on boilers are desirable as they show how much of the fuel they use is converted to useful heat. Selecting a boiler with high efficiency can result in substantial long-term savings.

The kind of fuel that the boiler runs on is another crucial thing to think about. Although many people choose gas because it is inexpensive and widely available, some homes may have access to other fuel sources like propane or oil. After accounting for things like fuel prices and environmental concerns, decide which fuel type is most practical and economical for your house.

It’s critical to assess the features and functionalities provided by various boilers in addition to efficiency and fuel type. To optimize energy consumption and personalize your heating schedule, look for models with sophisticated controls and programmable settings. Think about whether you need extra features like integrated hot water tanks or smart home system compatibility.

Finally, don’t overlook the boiler manufacturer’s standing and dependability. Seek out manufacturers who have a reputation for creating robust, high-quality boilers that are supported by first-rate customer support and warranty coverage. Gaining knowledge about the dependability and efficiency of various boiler models can be facilitated by reading other homeowners’ reviews and speaking with heating experts.

Considerations	Recommendations
Heating Needs	Calculate your home"s heating requirements based on size and insulation.
Efficiency	Look for a boiler with high efficiency ratings to save on energy bills.
Capacity	Choose a boiler with adequate capacity to meet your household"s hot water demands.
Space	Measure the available space for installation to ensure the boiler fits comfortably.
Brand Reputation	Research brands known for reliability and good customer support.

What are wall-mounted two-circuit gas boilers

The boiler and a flow (sometimes storage) water heater are combined into one device in gas wall-mounted two-circuit models that share the same dimensions and heating technical features. In two-circuit models, the sanitary water from the hot water supply circuit (HWS) is not combined with the heat carrier from the heating circuit.

In small to medium-sized residential homes up to 350–400 m2, where the distance between the boiler and the points of consumption is not too great (7–10 m), installed two-circuit models are recommended. If not, the process of heating and preparing running water will take excessively long—20 seconds or more—which will have an adverse effect on fuel and water consumption in addition to comfort.

The number of people residing in the home, or more accurately, the number of locations where hot water is consumed concurrently, is another crucial factor. The majority of two-circuit models function according to the DHW priority principle, which states that the heating circuit heats up when a consumption point is opened. Less frequently, but usually in more costly models where a three-way valve is used to achieve the capacity distribution, the heating circuit’s heating does not entirely stop, but the capacity is nonetheless decreased.

This effectively means that the DHW circuit’s capacity, let alone the heating circuit, may not be enough if multiple hot water consumption points are used simultaneously. As a result, there aren’t too many rooms overall that have hot water consumption points (kitchen, guest bathroom, etc.). д.) can’t be more than three.

Device and principle of operation

The only features that set two-circuit wall-mounted boilers apart from single-circuit boilers are the performance distribution bodies and extra heat exchanger between the circuits. The technical device may differ from model to model, but the general layout is straightforward and unambiguous: burner with gas supply and igniters → primary heat exchanger with coolant for the heating circuit and secondary heat exchanger with sanitary water circulation for the DHW circuit → system for removing combustion products to the chimney.

All well-known and popular models come from the factory pre-configured with every part and element required for the heating system, including the pressure gauge, automatic air vent, expansion tank, circulation pump, safety valve, and a number of sensors. Conventional two-circuit boilers come with every component required to run the heating system. д. This indicates that connecting the boiler’s supply and return lines and the water source (the boiler’s water supply, for example) for the DHW circuit is adequate for a typical heating system.

Let’s take a closer look at each circuit’s functionality in order to better comprehend the two-circuit model’s operating principle:

• heating – base circuit, in which the coolant continuously circulates, heating up in the heat exchanger and giving off heat through the radiators in the heated rooms;
• water heating – It is only activated when the hot water consumption point is opened, it redirects all or a certain part of the heating medium from the heating circuit to water heating.

Once the consumption tap is closed, the boiler returns to the heating circuit and, depending on whether the coolant has cooled down, either heats it up or, if the temperature is safe, goes into standby mode (background heating).

The supply of preheated water is always delayed in traditional two-circuit boilers (usually by five to fifteen seconds). However, there are models without this delay that have an integrated boiler and operate on the storage heater principle; we will go into further detail about these models when discussing the selection criteria. In any event, the length of the pipeline that carries the cooled water from the boiler to the point of consumption causes a boiler-independent delay in the hot water supply.

How to select a room thermostat to reduce monthly heating costs by up to 30%

Reviews of domestic wall mounted models with DHW circuit: advantages and disadvantages

Advantages	Disadvantages
Advantageous price – two-circuit models are only 10-15% more expensive than single-circuit, so it is the cheapest way to organize hot water supply in the house, compared to the installation of a gas column, electric boiler, etc.д.	Higher probability of failure – two-circuit models can work without problems for 10 or more years, but statistically the probability of failure in comparison with single-circuit models is higher, due to more complex design and extra. units
Compactness – two-circuit boilers only rarely differ in size from the same single-circuit analogs of the same manufacturer	Relatively large delay in hot water supply – can be solved by more expensive models with a built-in boiler
Simplicity of connection – a minimum of communications, connected to one point in contrast to the installation of separate devices for heating water	Limitation in performance – on average, the performance of DHW of common modern models in the range of 8-12 liters per minute, which is enough for a maximum of three, and according to the feedback of owners often only two points of simultaneous consumption
Availability of relatively inexpensive models with a built-in storage tank, solving the problems of comfort and, to some extent, performance	Energy dependence – all heating gas wall-mounted two-circuit boilers require connection to the power grid, despite the high demand, there are no energy-independent models due to the specifics of the design
Limitations in the use of antifreeze – most models are not designed for the use of antifreeze as a coolant and only some manufacturers allow the use of liquid of a certain brand, which is indicated in the instruction manual

How to choose a wall-mounted two-circuit gas boiler for a private house

Convection or condensation

First things first, as the type of boiler you have will impact its operation principle and, consequently, its efficiency:

• convection – traditional boiler, which accumulates heat energy exclusively from gas combustion in the combustion chamber, with some part of the heat going down the chimney with combustion products;
• condensing – more advanced, efficient and expensive design with one more additional heat exchanger accumulating the heat of condensate formed from flue gases. The temperature of waste gases at this principle of operation is 30-50 and more degrees lower, the heat energy accumulated by the additional heat exchanger is directed to heating the return line.

Of course, in the second scenario, the installation is much more efficient, and fuel savings can range from 15% to 20%, depending on the design. The true component of condensing boilers is a low-temperature heating system, which includes big radiators, continuous combustion at low power, and coolant that can reach 50°C. In this instance, the higher initial costs are recovered in three to five years of use. If not, condensing models have a 7–12 year payback period under current Russian conditions.

Condensing models range in price from 50,000 rubles to a maximum of 60,000 rubles; Korean and Chinese models, on the other hand, typically cost around 30,000 rubles. The high standards for the additional heat exchanger’s materials, which must withstand the condensate’s acidic effect, account for the high cost. Condensate, which is different from regular water, needs to be disposed of, which is another drawback of condensing models. All of the features have already been covered in great detail in the related article.

Every distinction and factor to consider when selecting condensing gas boilers

It is still sufficient to select a conventional convection boiler if you do not intend to set up a low-temperature heating system. We do not advise bothering with condensing models.

Structural device and material of the heat exchanger

Two heat exchangers, which can be joined or divided, are found in two-circuit boilers:

• bithermal heat exchanger – these are heat exchangers of the heating and DHW circuits combined in one inseparable construction, they are combined according to the "pipe-in-pipe" scheme, when sanitary hot water is in the inner pipe, and the heating circuit coolant is in the gap between the walls of the inner and outer pipes.
• monothermic heat exchangers – These are two separate traditional heat exchangers, one (primary) circulates the heat carrier of the heating circuit, the other – the sanitary water of the DHW circuit.

Even the hardest, non-changeable water in a heating system almost never forms a scale that obstructs circulation, though there are exceptions to this rule. The water in the DHW circuit is always changing, and as it heats up in the heat exchanger, it settles on the walls as scale, greatly reduces the coil’s diameter, and eventually clogs the entire thing.

However, a bithermal (dual) heat exchanger is nearly impossible to clean and must be replaced if it becomes clogged with scale. In contrast, two separate heat exchangers can be cleaned without any issues, even with mechanical methods. However, single-design models are less bulky and less expensive to manufacture than inventive and dependable boilers with two independent heat exchangers.

An equally significant factor influencing longevity and dependability is the substance used to construct the heat exchanger:

• steel – Steel heat exchangers are inexpensive to produce, light and plastic, not afraid of sharp thermal changes, but they are highly susceptible to corrosion, even despite good anti-corrosion coatings. Their service life is usually 10-14 years;
• copper – copper heat exchangers are more expensive, but also more heat conductive, more resistant to corrosion, their service life is about 14-17 years.

Presence of a storage tank

Different approaches can be used by contemporary wall-mounted boilers to prepare hot water:

• flow – the principle described earlier, in which the water starts to warm up when the point of consumption is opened;
• storage – the principle, in which there is always a certain volume of heated hot water in the built-in storage tank of the boiler.

We advise selecting a boiler with a storage tank, which can hold between 30 and 60 liters, if you use hot water frequently. The accumulation tank eliminates a 5–10 second preparation lag and provides a certain amount of preheated water in reserve, ensuring a more consistent temperature. It should be noted that these boilers are technically referred to as "single-circuit with built-in boilers," and they might fall under this category when looking through the online store’s product catalog.

Combustion chamber design and types of smoke extraction

All two-circuit gas boilers can be classified as follows based on how the oxygen required to support combustion is introduced and combustion products are extracted:

• with open combustion chamber (atmospheric boilers) – combustion air is taken from the room, through holes in the body, and the combustion products are discharged through a traditional vertical chimney;
• closed combustion chamber (turbine boilers)) – the air for combustion of fuel is taken from the street, through a coaxial chimney, with the help of it there is also the removal of combustion products.

The cost and ease of installation, the boiler’s purchase price, and the space requirements for installation are all determined by the type of combustion chamber.

Open combustion chamber and natural draught

Although they are less expensive, atmospheric boilers frequently have marginally fewer features. With the aid of a natural draft, combustion byproducts are released through a conventional vertical chimney. In order to confirm that a pipe with a 120 mm diameter and a 4-5 m length is needed, specific specifications are typically listed in the boiler’s documentation.

The drawbacks of atmospheric models include faster contamination and the requirement for routine cleaning of the burner, ignition electrodes, etc., in addition to their more difficult installation. Additionally, it is not advised to install them in living rooms (or in kitchens, hallways, etc.), as they require the same room’s oxygen for combustion. Instead, the boiler room must have adequate ventilation.

Closed combustion chamber and forced draught through a coaxial chimney

An overhead fan, or turbine, is a feature of boilers with closed combustion chambers that forces combustion products out of the boiler and encourages the combustion chamber to draw in fresh air. Because the turbine speed is automatically controlled and the boiler always maintains an ideal ratio of fuel to oxygen, turbine boilers are more economical and efficient.

The fact that a closed combustion chamber boiler eliminates the need to set up a complete, conventional chimney is a significant benefit. A coaxial (side) chimney is used for both air intake and gas removal. The inner pipe of the chimney is used to remove combustion products, and the space between the inner and outer pipes is used to bring in fresh air. The boiler comes with a coaxial chimney that is simple to install in a wall opening.

However, there are drawbacks even in this instance:

• the turbine at high speeds creates a certain noise, in some models it is quite noticeable, and in some models it is almost silent;
• Coaxial chimney can negatively affect the aesthetic appearance of the house;
• Turbine boilers consume 20-50 W more electricity.
• in terms of cost they are 3-5 thousand. rubles more expensive.

Selecting models with a closed combustion chamber is advised because they are safer, more effective, easier to install, and don’t need the room to be ventilated.

DHW performance

Regardless of capacity, the majority of contemporary wall-mounted, two-circuit boilers generate 8 to 12 liters of hot water per minute. It is worthwhile to concentrate on the DHW performance indicator at one of the later stages and only pay attention to significant deviations from the average values because this volume is more than sufficient for two points of consumption when opened to their maximum.

But you can figure out the maximum consumption to get a sense of how much the boiler output is sufficient for.

An average bathroom or kitchen faucet, for instance, has a flow capacity of three to five liters per minute. Of course, this depends on the head, diameter, and efficiency of the faucet (the ratio of air to water at the outlet).

EFFICIENCY

The boiler efficiency, or coefficient of performance (COP), is the ratio of the volume of fuel burned to the volume of heat released. For a contemporary wall-mounted boiler, an indicator between 89 and 92% is ideal. But, after figuring out the prior parameters, it is also important to pay attention to efficiency, as the difference of 1, 2, or even 3% will be expressed in tens of rubles per month rather than hundreds.

It is important to focus solely on indicators that score lower than 86%. By 2020, this will be considered unacceptable for quality wall-mounted gas boiler indicators due to technical flaws, and there will be a noticeable difference in operating costs when compared to models with an efficiency of 90% or higher.

How to change a private home’s gas boiler without breaking the law

Minimum required power

Selecting the capacity after choosing the model makes sense because modern models come in a variety of versions with varying heat output, typically ranging from 12 to 35 kW and beyond.

A typical uninsulated or inadequately insulated home in the Moscow region with two bricks for masonry and a ceiling height of 2.7 meters would need a minimum of 1 kW of heating equipment for every 10 square meters of heated space. Additionally, we advise having a capacity reserve of 15-20%, or 25–30% in the case of a two-circuit boiler.

For instance, the minimum power needed for the 150 m 2 house mentioned above would be 150/10 * 1.3 (30% reserve) = 19.5, or 20 kW.

In non-standard situations, such as when panoramic windows are used and the glazing area is significantly larger, when a house has high ceilings, perfect insulation, or is situated in the far north or south of the nation, consider the correction factors that could alter the outcome by 15–30%. With the calculator below, you can perform an in-depth calculation.

To sum up, it is important to discuss the factors that raise operating comfort and, consequently, boiler cost:

• The presence of a layer of sound insulation, seriously reducing the noise of the boiler;
• the presence of a programmer, which allows you to set a pattern of boiler operation for a day or a week;
• possibility to send notifications about malfunctions by SMS, with the help of GSM module, as well as control via Wi-Fi.

The best known manufacturers and models: characteristics and prices

The following models are the most popular and well-known, among the most reliable and trouble-free, and the best in terms of "price-quality" two-circuit wall-mounted boilers. It is challenging to rank them according to quality or dependability because the majority of them are the most popular models in the cutthroat industry, nearly identical when evaluated according to all criteria, but obviously unique in their own right.

BAXI ECO-4s 24F

The Italian two-circuit boiler with a closed combustion chamber that is most popular and "favorite" in Russia (named after the prefix "F"). It is distinguished by excellent economy and efficiency. With a maximum gas consumption of 2.73 m 3 per hour, it has one of the highest efficiency rates in the price range, at 92.9%. Simultaneously, the boiler is ideal for domestic settings: it can withstand slight voltage fluctuations, has variable gas and water pressure, and typically uses less clean coolant.

Copper serves as the primary heat exchanger, and nearly all protection systems available today include auto-diagnostics, circulation pump blocking, and overheating and freezing protection. pre-installed water filter as well. Excellent assembly and layout quality has allowed the boiler to operate trouble-free for more than six years of operation. The owners also observe that the system operates almost silently. The heated water’s slight temperature instability is the only drawback.

Vaillant turboFIT VUW 242/5-2

This is one of the greatest wall-mounted two-circuit gas boilers for heating a private home, in our opinion, despite its decreased popularity. One of the German reference models with a closed combustion chamber is the TurboFIT VUW 242/5-2. With an efficiency of 93.5 % and a maximum gas consumption of 2.66 m 3 per hour, it exhibits exceptional economy. It has separate heat exchangers, the main one being made of copper. A three-way valve, which helps to maintain the coolant’s temperature at open points of hot water consumption, facilitates the operation between the circuits. DHW performance concurrently at the analog level.

Since the model’s launch in 2017, there have been no known instances of service malfunctions. Nonetheless, the manufacturer has a long history of excellent durability and dependability. This model appears to be no different from the others based on its layout: all pipe connections are threaded, made of copper rather than rubber, and have excellent build quality. There are all the defenses that are required. The servo, ignition, and turbine are remarkably quiet.

The only drawback is its increased cost; however, this is actually a low-cost model from a reputable high-end manufacturer. It is also important to keep in mind that, in order to avoid the electronic control board from failing, it is preferable to connect the boiler through a voltage stabilizer.

Viessmann Vitopend 100-W A1JB010 24

An additional citation German boiler with closed combustion chamber; performance is marginally lower than that of the Vaillant turboFIT. 91% efficiency at the highest gas consumption of 2,77 m 3 per hour. Separate heat exchangers are used; the main one is made of steel but has thick walls and is intended to withstand working pressures of up to 3 bar. No leaks or fires have been reported during Russian operations. Productivity is distributed among the circuits through a three-way valve, and all safety mechanisms are present.

One notable distinction is the inclusion of a programmer that lets you program the boiler’s settings for a day or a week, which, when used skillfully, can drastically cut down on consumption. An uncommon feature in boilers in this price range is an integrated programmer.

Consistency with most Viessmann models means that they are vulnerable to voltage fluctuations (the protection mechanism is only intended for 170–253 V, which is insufficient in most cases), and once more, we advise connecting through a voltage stabilizer for the boiler. In rare instances, the burner module and flame sensor may become clogged, which would cause the automation to display error F4. Regular boiler cleaning (at least once every three to four years) and gas filter inspection are required.

Bosch Gaz 6000 WBN 6000-24 C

Though not the best in terms of performance, this well-known manufacturer’s budget model has been successfully used in the past. The heat exchangers are independent, with the primary one being made of copper, and a three-way valve is used to distribute performance between them. The maximum gas flow rate is 2.8 cubic meters per hour. operates almost silently, especially when compared to the reference Vaillant, especially with the smooth ignition technology and the absence of the distinctive clap.

The tool and the materials utilized are essentially the same as in earlier analogs; however, some connections are rubber-based rather than threaded. Although the technical dependability of major complaints is generally unknown, the boiler is extremely picky about the existence of a grounding, ideally one that is dedicated to the boiler alone; if not, it will continuously generate an error EA.

Detailed instructions for grounding a private home’s gas boiler

Additionally, owners frequently complain about less convenient control—instead of using individual buttons or "twists" like in earlier models, you now need to perform multiple actions to change the temperature of the DHW circuit and some other settings.

Buderus Logamax U072-24K

German boiler model with closed combustion chamber that was localized for Russia (assembly is done at a Russian factory), making it stand out from the competition and considerably lowering the boiler’s cost. 92% efficiency, 2.8 m 3 of gas per hour at maximum use, and copper as the primary heat exchanger. The boiler’s design is largely similar to its earlier German counterparts, with threaded connections; however, the Russian assembly’s quality occasionally falls short of that of the European counterpart.

Overall, this model is incredibly affordable, effective, dependable, and fashionable, but it also has a few more drawbacks than advantages. Firstly, apart from the substandard assembly, the makeup tap is made of plastic, which is prone to breaking with time. Second, variations in voltage could harm the electronic board. However, the boiler’s cost makes it competitive and deserving of notice.

Ariston ALTEAS X 24 FF NG

High-tech, incredibly fashionable, and efficient boiler featuring a closed combustion chamber. 93.7% efficiency, a maximum gas flow rate of 2,73 m 3 per hour, independent heat exchangers, and three-way valve distribution mechanism. Apart from the build quality and design, the primary distinction from earlier models is the inclusion of a programmer and the capability to operate through a smartphone application via Wi-Fi. The owners also observe a great deal of minor adjustments (coolant temperature limitation, control over on/off frequency, and t.д.).

The only drawbacks are an interface that can be challenging to use, an impractical glass coating that shows fingerprints, and a relatively expensive price that is hardly excessive.

It is impossible to include a list of all the excellent models made by the same or different manufacturers in this article, as they are all undoubtedly superior in some aspects and inferior in others.

You can also consider looking at the models from companies like Protherm, Lamborghini, MORA-TOP, De Dietrich, and Wolf, if you’d like. We do not advise choosing cost-effective Korean models, boilers made in Russia, or boilers that are similar to them (with assembly in China) due to the rising problems and quality.

Choosing a gas wall-mounted two-circuit boiler for your home is a crucial decision that affects both your comfort and energy efficiency. Firstly, consider your heating and hot water needs to determine the boiler"s size and capacity. Next, prioritize energy efficiency ratings to save on utility bills in the long run. Look for models with high AFUE (Annual Fuel Utilization Efficiency) ratings, indicating better efficiency. Additionally, opt for boilers with modern features like programmable thermostats and smart controls for convenient operation and energy savings. Pay attention to reliability and warranty coverage to ensure peace of mind and minimal maintenance hassle. Lastly, consult with a professional installer to ensure proper sizing, installation, and compatibility with your home"s heating system. By considering these factors, you can select the best gas wall-mounted two-circuit boiler to keep your home cozy and cost-effective.

Prices: summary table

Model	EFFICIENCY, %	Max gas flow rate, m 3 /hour	DHW capacity, l/min at t 30°C	Cost, rubles.
BAXI ECO-4s 24F	92,9	2,73	9.8 at t 35°C	43 200-47 500
Vaillant turboFIT VUW 242/5-2	93,5	2,66	11	45 000-53 200
Viessmann Vitopend 100-W A1JB010	91	2,77	11,2	54 000-61 000
Bosch Gaz 6000 WBN 6000-24 C	93,2	2,8	11,4	39 800-42 000
Buderus Logamax U072-24K	92	2,8	11,4	43 500-52 500
Ariston ALTEAS X 24 FF NG	93,7	2,73	9.6 at t 35°C	64 200-69 000

Selecting a gas wall-mounted two-circuit boiler is an important choice for the insulation and heating of your house. Before making a decision, it is important to take a few things into account.

First, determine how much hot water and heating your home needs. Take into account your home’s dimensions as well as the quantity of bathrooms and radiators it has. In order to meet the demand for hot water and heating, a larger home with more bathrooms and radiators will probably need a more powerful boiler.

Consider energy efficiency next. Selecting high-efficiency boilers can lower your energy costs and have a smaller negative impact on the environment. Although energy-efficient models may initially cost more, over time they may save more money.

Take into account the boiler manufacturer’s reputation and dependability as well. Select a brand that is well-known for manufacturing dependable, high-quality goods. Examining homeowner reviews can also offer insightful information about the longevity and functionality of various boiler models.

When comparing boilers, look for features like modulation technology, which enables the boiler to more effectively adjust its output to match the heating demand. This can further cut energy use while enhancing comfort.

Finally, don’t overlook upkeep and installation. Select a boiler that has a thorough warranty and is simple to install. When making your choice, don’t forget to take the cost of servicing and the accessibility of replacement parts into account.

To sum up, choosing the correct gas wall-mounted two-circuit boiler is essential to maintaining a warm and cozy home while controlling energy expenses. You can make an informed choice that will benefit your house for many years to come by taking into account elements like the needs of your household, energy efficiency, manufacturer reputation, and maintenance requirements.

Video on the topic

A two-circuit boiler is the best option for most homes!

How to choose a boiler? Sort out the top 5 wall-mounted boilers (Baxi, Buderus, Fondital, Italtherm, Protherm)