How to choose a gas floor standing double-circuit boiler

Selecting the ideal gas floor-standing double-circuit boiler is essential for a home’s effective hot water and heating systems. It can be difficult to choose wisely when there are so many options on the market. To make sure you invest in a boiler that suits your needs, you can streamline the selection process by being aware of the important variables and considerations.

Floor-standing gas The capacity of double-circuit boilers to supply hot water and heat in homes makes them popular. Double-circuit boilers are perfect for larger households or properties with high hot water demand because they can heat and provide hot water simultaneously, unlike single-circuit boilers. They are efficient and convenient, but selecting the best one needs careful consideration.

The size and heating capacity of a gas floor standing double-circuit boiler are important factors to take into account. For your home’s heating needs, the boiler’s size should be suitable. The size of boiler needed depends on a number of factors, including the number of occupants, insulation levels, and property size. While an undersized boiler might find it difficult to meet heating demands, an oversized boiler can result in energy waste.

Another important consideration when selecting a gas floor-standing double-circuit boiler is efficiency. Choosing an extremely efficient model can save energy costs and have a smaller environmental impact. Seek for boilers that convert fuel into heat as efficiently as possible, as indicated by high Annual Fuel Utilization Efficiency (AFUE) ratings. Furthermore, take into account features like modulation technology, which further improves efficiency by adjusting the boiler’s output to match the heating demand.

Considerations like durability and reliability are crucial if you want to make sure your investment pays off in the long run. Select a reliable brand with a solid reputation for producing reliable, high-quality boilers. Evaluating consumer feedback and consulting with heating experts can assist you in determining the dependability and longevity of various boiler types.

Factors to Consider	Considerations
Heating Capacity	Determine the appropriate size based on your home"s square footage and heating needs.
Energy Efficiency	Look for high-efficiency models to save on energy bills and reduce environmental impact.
Hot Water Demand	Assess your household"s hot water usage to ensure the boiler can meet your needs.
Brand Reputation	Research reputable brands known for reliability and quality.
Installation Requirements	Consider installation space, ventilation needs, and compatibility with existing systems.
Warranty and Support	Check warranty coverage and availability of customer support for maintenance and repairs.

What are two-circuit floor standing gas boilers?

A floor-standing gas two-circuit boiler is a device that simultaneously functions as a flow water heater and a boiler. Its distribution of the coolant and hot water on separate circuits ensures that they are never mixed together.

Although the specific model of these boilers determines its technical device, the general design is nearly always the same:

• gas burner and ignition element;
• starter and main igniters;
• system for gas and smoke extraction;
• combustion chamber and heat exchanger.

Additional components for the floor-standing, two-circuit gas boiler are optional and include an expansion tank, a blower fan, a circulation pump, an automatic control module, electronic sensors, and safety valves to regulate the equipment’s safety and enhance performance.

Installing gas floor-standing two-circuit boilers is a convenient option for reasonably small residential homes (between 50 and 400 square meters), as they eliminate the need for a lengthy pipeline (7-8 meters) to supply hot water. If not, too much fuel would be used to heat the running water over an extended period of time.

Taking into account the number of occupants in the house is also crucial because, in most cases, the water supply gets priority when there are two circuits. This effectively means that even with excess capacity, the volume of hot water produced will never be sufficient if multiple points are used simultaneously. Consequently, there shouldn’t be more than three rooms—the bathroom, kitchen, and laundry room—that have hot water consumption points combined.

Operating principle

Take into consideration how each of the two-circuit gas boiler’s circuits operates independently in order to comprehend the general principle of operation:

• heating – constantly "runs" the heated coolant through itself, which transfers the heat to the surrounding space in the rooms via the radiators;
• water heating – is activated by switching on the three-way valve, which redirects part of the heat transfer medium to heat the tap water.

Therefore, the house’s heating is either completely shut off (using the "DHW priority" principle) or very limited (using the three-way valve) during periods of active water use. Because of this, the temperature of the water that is running stays constant, irrespective of the pressure head, the quantity of open taps (as long as they are kept within allowable limits), and the pressure within the gas mains.

The three-way valve returns to the heating circuit when the hot water tap is closed. The system resumes heat energy production to heat the coolant if it has had time to cool, and if the temperature is stable, it enters standby mode (background heating).

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Reviews of floor standing gas boilers with a circuit for DHW: advantages and disadvantages

Benefits and drawbacks of dual-circuit gas boilers If you pay attention to the advice and evaluations of more seasoned owners, you can evaluate floor standing boilers ahead of time.

Advantages	Disadvantages
favorable price – a two-circuit device is much cheaper than a conventional boiler and water heater separately	Dependence of nodes – in case of failure of one of the circuits immediately turns off both water heating and heating of the house
compactness – the size of such a boiler is almost the same as its single-circuit counterpart, which allows you to save space	Cost of maintenance – as a rule, installation, repair and adjustment of units with two circuits is more expensive than standard ones
clear connection – connecting gas to just one point simplifies documentation, installation and repair of the system	separate placement – powerful floor standing boilers (more than 30 kW) can be placed only outside the living area
service life – floor models with two circuits last much longer than suspended (wall-mounted) equipment	the need for authorization – installation and replacement of gas equipment must be coordinated in the city authorities

Additionally, some owners have reported that their boilers stop operating during very cold snaps. Although there is a flame, it is obviously insufficient for heating. This happens when the mains’ pressure drops, but it’s not a drawback—all you have to do is pick the model that best fits your climate.

Choosing the right gas floor-standing double-circuit boiler is crucial for efficiently heating your home and providing hot water. When making this decision, consider factors like the size of your home, your hot water needs, and your budget. Look for boilers with high energy efficiency ratings to save on utility bills and reduce environmental impact. Additionally, prioritize boilers with reliable safety features and easy-to-use controls for peace of mind and convenience. Take into account the reputation of the manufacturer and read reviews from other homeowners to ensure you"re investing in a quality product. By carefully evaluating your options and considering your specific requirements, you can select a gas floor-standing double-circuit boiler that meets your heating and hot water needs effectively and efficiently.

How to choose a gas two-circuit floor standing boiler?

The dual circuit gas boiler’s suitability for the current water supply circumstances should be ascertained first. The system’s overall performance suffers greatly from even brief disruptions in the cold water supply, which can also result in catastrophic equipment failures.

The appliance’s engineering design is also determined by its quality and functionality, so a few factors must be carefully taken into account.

Convection or condensing principle of operation

The way in which the heat energy released during gas combustion is utilized determines how efficient a two-circuit gas boiler is:

• convectional – uses for heating only the energy obtained from the direct combustion of gas, with most of the heat leaving the combustion chamber with the smoke;
• condensing – uses for heating both the energy obtained from gas combustion and the energy of water vapor contained in the waste products of combustion.

Of course, the second approach makes more financial sense because it raises equipment efficiency by 15–25%. Deep cooling of the smoke and steam condensation in a low-temperature auxiliary heat exchanger (water economizer) "extract" additional heat.

Condensing appliances have a higher initial cost than conventional appliances—they are 1.5–2 times more expensive—but after 3–5 years of use, their cost is recovered.

It should be considered that there will be a need to dispose of the daily formed* condensate. This liquid cannot be emptied into the septic tank or local drainage system due to the acid content, so a plan for neutralizing it must be in place beforehand. This restriction does not matter, though, if a boiler with a capacity of no more than 30 to 35 kW is to be purchased, as long as direct access to centralized sewerage is available in the room where the boiler will be installed.

* Domestic boilers with 15–24 kW on average generate 20–35 liters of condensate every day.

Later on, the boiler’s functionality can be increased by connecting additional features, like heated floors. However, utilizing convection for such an action is strictly prohibited.

Structural device and material of the heat exchanger

The heat exchanger design of a two-circuit boiler is different from that of a single-circuit boiler because it can have both a combined and separate device:

• bithermal – combines in a common body the DHW and WHS circuit according to the scheme "pipe-in-pipe", with hot water for distribution in the inner pipe, and the coolant for heating the room – in the gap between the walls of the pipes;
• monothermal – is formed of two parts (are separate from each other, but are considered one part), in the first (primary) heats the coolant for radiators, and in the second (plate) – water for personal use.

Limescale will be minimal because the coolant circulates in a circle and heating is a closed system. The situation is reversed when heating running water; scale forms continuously and in large volumes (depending on the water’s hardness), necessitating periodic cleaning or replacement (if cleaning isn’t done).

Monothermal heat exchanger is more reliable in terms of maintenance and maintainability, it is quite easy to wash it, and if it completely clogs or fails, it can be partially "renewed". In the case of bithermal analog will have to change the whole device, which will subsequently be much more expensive. Also the unit with separate heat exchangers is more convenient in everyday operation, t. к. in it both circuits work independently of each other, which allows not to close the heating circuit during the use of hot water.

The kind of material used to construct the heat exchanger has an impact on the heating equipment’s dependability and service life in addition to its design:

• cast iron – is characterized by high heat resistance and resistance to corrosion, so it can work for decades (30-50 years), but it is very heavy, poorly tolerates sudden temperature and pressure spikes and mechanical shocks;
• steel – cast iron is more plastic and lightweight, is not demanding to operating conditions, is not afraid of thermal fluctuations and is easy to repair, but it is prone to rusting and rusting, so it is generally short-lived (10-12 years);
• copper – combines the best qualities of cast iron and steel, t. ч. corrosion resistance, durability (15-20 years) and high thermal conductivity, as well as it is immune to acids, making it suitable for condensing boilers;
• siluminous – is used exclusively in harsh conditions of condensation appliances, because it is this alloy of aluminum and silicon better than other metals resist the action of chemically aggressive substances.

Shape-wise, cast heat exchangers are better in any case because welded seams damage the material’s structure and reduce its resistance to corrosion.

Presence of a storage tank

The process of preparing water for the hot water supply is the next factor to take into account when selecting a floor gas two-circuit boiler:

• flow-through – After opening the faucet, the water instantly starts to heat up;
• storage – water is heated for a long time in a special tank.

Selecting a boiler with a storage tank, whose capacity varies based on the model, is advised when using hot water intensively (or equip the system with it). In any scenario, a single person should have a 40–50 liter reserve; a family of four, for instance, needs a minimum of 120–180 liters.

Models with an integrated boiler also have the benefit of maintaining the water’s predetermined temperature and balancing the system pressure.

Energy dependent or non-volatile

A non-independent gas boiler operates independently without a power source. The only mechanical thermoregulator that controls the coolant’s heating comes from the automatics, so piezo ignition must be used each time they are started.

These kinds of devices are utilized in water circulation systems that, in the case of two-circuit models, are not always efficient. In this regard, it is advised to plan ahead for the distribution of the two-pipe heating pipe during installation; the collector type of decoupling is the best subspecies.

Energy-independent boilers are connected to a separate boiler if needed because they cannot have a storage tank installed.

An energy-dependent gas boiler uses electricity for ignition and can only run when it is permanently connected to the mains. The circulation pump and the control board, which has the lowest power consumption among the A++ class equipment, are the primary electricity-consuming components.

These devices independently control the gas supply, flame power, and many other subtleties. They also react to temperature changes in the room more precisely and rapidly. They allow you to program a specific mode of operation for a day or a week ahead of time. This results in a fuel consumption decrease of 20–30%.

Power surges frequently cause energy-dependent appliances to malfunction. The cost of repairs can range from 30 to 50 percent of the boiler’s purchase price, just to replace a few parts. Installing a voltage stabilizer is even required by many manufacturers in order to maintain the warranty.

Combustion chamber design and types of smoke removal

Based on the way in which oxygen is supplied to the furnace (which is necessary to keep the flame active), all two-circuit gas boilers fall into two categories:

• open type combustion chamber (atmospheric boilers) – draw air directly from the room in which the equipment is installed;
• closed combustion chamber (turbo boilers) – do not draw heated air from the room, but take it from the street through a coaxial chimney, which reduces heat loss.

The exact arrangement of the combustion product output—through a shaft on the house roof or straight through the wall—depends on the type of combustion chamber.

Open combustion chamber and natural draft through the chimney

Flue gases are expelled from boilers with an open combustion chamber and a natural draft by means of a fully functional vertical chimney that exits through the roof. Because this construction only has one simple device, it is less expensive and, in theory, more reliable. However, installing atmospheric boilers is a difficult task.

Such boilers may only be installed apart from living rooms, as long as all boiler room and chimney organization guidelines are followed:

• diameter of the chimney pipe is at least 130-140 mm and the length is 3-4 m;
• it is made of stainless acid-resistant steel or asbestos;
• the minimum boiler room area is 3.5-3.7 m 2 with a ceiling height of 2.2-2.5 m;
• the room has at least one window of 0,6-0,7 m 2 and good ventilation.

It makes more sense to choose an appliance with a closed combustion chamber and a chimney outlet through the wall if at least one of the aforementioned guidelines is broken. If not, the equipment will, at best, just stop working and, at worst, potentially fatal levels of carbon monoxide will begin to build up in the space.

Closed combustion chamber and natural draught through a coaxial chimney

Boilers with parapet gas are neither wall-mounted nor floor-standing. They are distinguished not only by their positioning but also by the holes in their bodies, which allow them to function as radiators and provide heat to the space in which they are installed. They require a coaxial chimney, which is made up of two pipes inserted into one another. Air from the street is drawn in through the middle gap, and smoke is expelled through the inner part.

The main location for such equipment is below the window sill line (instead of a battery, for example), and it can be installed in any type of building, including residential, commercial, and even high-rise apartment buildings. The pipes’ horizontal section should not extend beyond 2.8–3.0 meters, which is the only restriction.

Closed combustion chamber and forced draft

An inflatable fan, or turbine, is a feature of boilers with closed combustion chambers. Its purpose is to forcefully release smoke from the furnace into the street and automatically pull in fresh air through the same coaxial pipe. Installing the devices is simple and does not require any changes to the boiler room’s layout or dimensions.

The primary benefit of the turbine unit is that it is sealed off from open fire sources, minimizing the possibility of carbon monoxide seeping into the house.

Gas boilers with a closed combustion chamber are typically installed in buildings for any kind of use, but there are a few things to consider:

• the turbine in the boiler creates a little extra noise;
• the coaxial pipe is led through, which affects the appearance of the wall;
• Smoke output at eye level does not allow you to stay closer than 4-6 meters from the chimney outside the house;
• The turbine unit consumes 40-50 W/h more than a standard chimney unit.

Forced-draught appliances cost more than conventional ones, but they are less expensive to install because they don’t need a complete chimney to be built.

Requirements for selecting modern turbo gas boilers with competence

It is evident that different types of combustion chambers and smoke removal systems differ from one another, but they are all made to operate safely and effectively in two-circuit gas boilers. Therefore, the buyer’s financial situation and the particular operating conditions have a greater influence on the final model selection.

Efficiency and gas consumption

The heating boiler’s efficiency coefficient is a performance indicator that directly influences how economically it uses energy resources.

The efficiency value ranges from 90–98% for standard gas units and from 104–116% for condensing models. Physically speaking, this is not possible; in fact, convection boilers have an efficiency of 86–94% and condensing boilers of 96–98%, depending on how much of the released heat is considered.

GOST 5542-2014 states that 9.3 kW of energy can be produced from 1 m 3 of gas. With a boiler operating for one hour at 100% efficiency and an average heat loss of 10 kW, the ideal fuel consumption is 0.93 m³. Thus, for instance, the ideal gas consumption for a 16–20 kW domestic boiler with a standard efficiency of 87-82% is 1.4–2.2 m 3 /h.

Minimum required capacity

The size of the house is the main factor in determining the unit capacity. Thus, the following formula is used to determine the minimal amount of power needed for heating:

Q is equal to S × 100.

Q is the needed power (kW), S is the total heated area (m2), and 100 is the power rate per unit area at the house’s average heat loss (W/m2).

For instance, Q=150×100=15 kW would be needed to heat a 150 m² residential home.

But since we’re talking about a two-circuit boiler, we also need to add another 25–30% to this figure to account for the needs of the hot water supply. To prevent the device from being used to its maximum potential, experts advise adding 10–20% more to the total reserve—that is, Q = 21–22 kW for a 150 m³ house.

Avoid selecting a unit whose capacity exceeds the requirements of the space. Wear on the machinery and fuel consumption will rise as a result. However, the number of hot water distribution points increases if the house has, say, two bathrooms, so this is something else to consider when purchasing a boiler.

In non-standard cases, in addition to the building’s square footage, the height of the ceilings, the building’s insulation level, the kind of roof, the quantity of windows and exterior doors, the storey, and the climate-specific features of the area must all be considered in order to determine more accurate power indicators. A specialized calculator can be used to perform the calculation; add 15-20% power reserve to the total result for the entire house after adding the figures for each room.

The possibility of using antifreeze

In the event that a private residence is intended for seasonal living or extended periods of absence, it is imperative to prevent the simple fluid in the system from freezing in order to protect the pipes. One way to accomplish this is to either completely drain the coolant or add antifreeze, a chemical that, even at extremely low negative temperatures, neither freezes nor hardens but instead transforms into a gel without growing in size.

Antifreeze should generally not be used in two-circuit gas boilers. If the instructions specify that the heating system’s coolant should only be water, it is best to avoid taking a chance. Any issues arising from the application of any solutions are not covered by warranties.

Certain brands of antifreeze can be poured into some manufacturers’ units. However, what works for one model might not work for another, so this is something that should be decided upon beforehand. Occasionally, products with a list of appropriate equipment indicated can be used.

Additional criteria

Once you’ve established the fundamental specifications of the two-circuit gas boiler, you can focus on a few more crucial features:

• electricity consumption (in energy-dependent appliances) – on average, such equipment consumes about 2.0-2.5 kW per day, for a month it comes out to 60-75 kW;
• maximum possible water temperature – as a rule, water can be heated to + 55 … + 65 °C in the DHW circuit and to + 80 … + 90 °C in the DHW circuit;
• heating circuit operating pressure – the majority of two-circuit floor standing gas units function normally in the range of 2-4 bar, the operating pressure primarily depends on the material and thickness of the heat exchanger;
• hot water supply capacity – the volume of liquid, which the device can heat up to the set temperature in 1 minute, is 2.5-30 liters;
• automatics functionality – realization of safety functions is in any case obligatory, but in many models attention is paid to convenience of operation as well.

The following modules are the primary automated components that enable you to either fully or partially relieve a person from direct involvement in boiler control: self-diagnosis, auto ignition, flame modulation (regulation), external GPS-control system, and programmer (scheduler).

The best known manufacturers and models: prices and characteristics

The functionality and quality of two-circuit gas heaters are primarily determined by the nation of manufacture; it is advised to purchase equipment from European, South Korean, or even Russian manufacturers rather than purchasing untested equipment from Chinese vendors.

It is important to consider whether the boiler is appropriate for the local climate and gas supply conditions.For instance, in Asia, gas supply and pressure drop outages are rare, but in post-Soviet countries, they occur frequently. As a result, models for these countries are tailored to local conditions.

Baxi SLIM 2.230 I

The most popular 22.1 kW Italian boiler unit, as demonstrated by decades of use. features an integrated 65-liter boiler, a circulation pump, and an open combustion chamber. It is constructed from premium components, including a stainless steel burner and a gray cast iron primary heat exchanger. Gas consumption at maximum: 2.59 m 3 /h.

Italy-based manufacturer Baxi (Baxi).

Protherm Bear 20 KLZ

Another dependable model with a 17 kW capacity that offers five preset modes for a wide range of temperature regulation. has a substantial 90-liter storage capacity and a sturdy cast iron heat exchanger. Uses up to 2 m 3 of fuel per hour when running at maximum power.

Slovakian manufacturer Protherm (Protherm).

Zhukovsky AKGV-17,4-Z ZhUK

17.4 kW gas two-circuit floor-standing boiler for domestic use that uses no energy. uses 1.87 m 3 of gas per hour at its maximum. Because the design does not include a water heating boiler and instead uses a basic steel heat exchanger, the unit is generally fairly cheap.

Manufacturer Zhukovsky (ZhMZ), Russia is the manufacturer.

Lemax Premium-16 B

Excellent 16 kW Russian-made boiler that is almost completely trouble-free. Its small size allows for the maximum area of heat exchange, allowing you to use as little as 0.95 m 3 of gas per hour. Even when compared to similar models in more expensive price ranges, this model is among the most cost-effective. Additionally, there is a unique heat exchanger composed of 2 mm enameled steel that is resistant to mineral oils and salt, extending its service life to 12–14 years.

Russian manufacturer Lemax (Lemax).

Fondital Bali BTFS E 32 V

This 32 kW gas floor standing double-circuit boiler from Italy is a high-quality, long-lasting model that’s ideal for heating a private home. distinguished by a closed combustion chamber, a layer of thermal insulation, the use of premium materials, and nearly silent operation. uses the "AquaPemium" system, which consists of a 60-liter boiler, a filter, and secondary and primary heat exchangers made of copper and steel, to produce DHW. Maximum gas flow rate: 3.64 m 3 /h.

The only drawbacks are their high price, bulky weight, and insufficient availability of skilled service professionals in some areas of Russia.

Italian manufacturer Fondital (Fondital).

Prices: summary table

Two-circuit floor-standing gas boilers are rated similarly:

Model name	DHW circuit capacity, l/min.	Power, kW	Gas consumption, m 3 /h.	Price, rub.
Baxi SLIM 2.230 I	13,4	22,1	≤ 2,59	125 000
Protherm Bear KLZ	12,0	17,0	≤ 2,00	158 500
ZHMZ AKGV-3 ZHUK	5,4	17,4	≤ 1,87	34 000
Lemax Premium-B	6,0	16,0	≤ 0,95	30 000
Fondital Bali BTFS E V	24,5	32,0	≤ 3,64	167 500

Selecting the ideal gas floor-standing double-circuit boiler is essential to guaranteeing your home’s effective hot water and heating systems. With so many things to take into account, it’s critical to make an informed choice that fits both your needs and your budget.

The size of your house and your heating needs should be your top priorities. A gas double-circuit floor boiler is available in different sizes and heat outputs. Ensuring optimal performance and energy efficiency is ensured by choosing one that corresponds with the size of your property.

Additionally, take note of the boiler’s energy efficiency rating. Choosing a model with a high efficiency rating lowers your carbon footprint and lowers your energy costs. Seek for boilers that have earned the Energy Star label or that adhere to other industry efficiency requirements.

An additional important consideration is the boiler’s brand and dependability. Select a reliable producer who has a track record of creating long-lasting, high-quality heating appliances. Assessing the dependability and efficiency of various boiler brands can be facilitated by reading customer reviews and getting recommendations.

Additionally, remember to evaluate the boiler’s installation and maintenance needs. While some models are made for simple DIY installation, others might require professional installation. When selecting a boiler, don’t forget to take the accessibility of replacement parts and ease of maintenance into account.

Finally, consider your financial constraints when choosing a double-circuit gas floor standing boiler. Even though it can be tempting to go with the least expensive option, making the investment in a higher-quality, more efficient boiler can save money in the long run. To determine which model strikes the best balance between performance and affordability, compare features and prices across various models.

Through careful consideration of various factors like installation requirements, energy efficiency, size, budget, and reliability, you can select the best gas floor standing double-circuit boiler to efficiently meet your home’s heating needs. Your household can enjoy years of dependable and effective heating and hot water supply if you make an informed decision up front.

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