Gas double-circuit wall-mounted boiler - which is better?

Rating of the TOP 15 best double-circuit gas boilers of 2021

Structure and main differences

A gas boiler consists of three main modules - a burner, a heat exchanger, and automatic control. The burner is located in the combustion chamber, above it there is a heat exchanger in which the coolant is heated. The entire process is controlled by automation. It ensures safety and changes the operating modes of the equipment.

Boiler with a closed combustion chamber (turbocharged)

Types of heat exchangers

A double-circuit boiler is distinguished by the fact that it can heat both water for heating and water supply. This must be done separately, because special heat exchangers are needed. There are two types:

• Double heat exchanger. It consists of two separate modules - primary and plate. In the primary, the coolant from the heating system is heated, in the secondary - plate - water for domestic needs. The primary heat exchanger is a tube with fins, the secondary is a set of plates. They are located in different parts of the boiler - primary at the top, plate at the bottom, but they are connected to each other so they can be read as a single part.
• Bithermal heat exchanger. It consists of two metal tubes of different diameters inserted into one another. In the inner tube, water is heated for hot water supply, in the outer tube - for the heating system.

The structure of a double-circuit gas boiler

A system with a dual heat exchanger is more reliable. Since heating is a closed system and the coolant circulates in a circle, little scale is formed. When heating water for hot water supply, the situation is the opposite - running water heats up, which means there is a lot of scale. This part of the heat exchanger periodically requires repair or replacement. If in a dual heat exchanger it is possible to replace only the part that heats water for domestic needs, then in a bithermal heat exchanger there is no separation; you have to change the entire device, and this is much more expensive. There is one more point: a double-circuit gas boiler with a double heat exchanger works normally for heating, but with a bithermic the situation is different - it does not work at all.

How to choose and what to pay attention to?

1. Control method : single stage. two-stage or three-stage. Two-stage boilers adapt best to daily and seasonal temperature changes.
2. Heat exchanger type : separate or bithermic devices. Separate ones have 2 heat exchangers: one for heating, the second for hot water supply. In such boilers, scale does not form and boiling of water is eliminated, but they are more expensive. Bithermic ones have double elements, the disadvantages are worse cross-country ability and scale formation.
3. Automation : mechanical or electronic. Electronic ones are more expensive, but in case of problems with electronics, additional repair costs are required.

Which heat exchanger to choose?

When choosing a double-circuit heating boiler, you have to decide whether to buy a boiler with a bithermic heat exchanger or with separate heat exchangers. You will have to decide, because there is no clear answer. Here are the criteria:

• With bithermic, water for hot water heats up faster, since heating comes directly from the burner flame. That is, you spend less water while it heats up, and less gas and electricity is wasted.
• Since the heating is direct, the temperature is maintained more accurately.

  
  Deciding on a heat exchanger is not so easy

• For models with separate heat exchangers, they are less likely to clog. In addition, it is possible to replace only one of the heat exchangers.
• If the bithermic “flies”, both heating and hot water supply do not work. In a boiler with separate heat exchangers, if the secondary one fails, the heating will continue to operate.
• As practice shows, it can be very difficult to flush a “neglected” bithermal heat exchanger. Plate-type ones, after washing, may be inoperative (the plates are at a distance of 2-3 mm from one another). But if the heat exchanger is of a collapsible type, it can be disassembled, cleaned and put back together. So problems can only arise with brazed plate heat exchangers. We recommend reading the article on how to clean a heat exchanger.
• Bithermic ones have less throughput - the pipe is divided into sections. To ensure the same water consumption, it is necessary to take more expensive models (due to the greater consumption of expensive metals for more efficient heat exchangers).
• In summer mode (without heating), a bithermic heat exchanger is more economical.
• As a rule, a bithermal heat exchanger costs more than two separate ones.

Opinion of the site editors . We recommend purchasing heating boilers with separate heat exchangers.

Now you not only know how a double-circuit boiler works, but also what heat exchangers can be installed in it.

The best double-circuit gas boilers in terms of price, quality and reliability

BAXI ECO-4s 24F 24 kW

A mid-priced convection boiler that can be installed in any room: bedroom or kitchen.

Works on both natural and liquefied gas. A closed combustion chamber allows you to spend less gas on heating, while the heating output remains high.

The primary heat exchanger is made of copper, the secondary one is made of stainless steel. There is a built-in circulation pump and expansion tank.

The display is installed on the case, there is also a thermometer, pressure gauge, and power-on indication. It is allowed to connect a separate chimney (with a diameter of no more than 80 mm) .

An air vent, safety valve and gas control are installed as protection.

The water is purified using an internal filter . Weighs 30 kg. Service life - 10 years, warranty period - 2 years. This model has proven itself well in 2021.

Specifications:

• Thermal power: 9.30 - 24 kW;
• Thermal load: 10.60 - 25.80 kW;
• Dimensions: 400x730x299 mm.

pros

• pump blocking protection;
• connection of a warm floor,
• flame modulation;
• auto diagnostics;
• frost protection;
• heats liquid quickly;
• silent;
• reliable components.

Minuses

• You cannot adjust the power yourself.

Buderus Logamax U072-12K 12 kW

This model has received many positive customer reviews: users describe it as a reliable and convenient wall-mounted unit with a high level of safety and almost silent.

Changes in electricity and pressure do not affect its performance in any way. The power is enough to heat an area of ​​up to 350 sq.m.

The kit includes: pump, expansion tank, flow sensor, safety valve and control and safety device.

The size of the boiler allows it to be placed even in a small room: for example, a pantry or bathroom.

Index “K” means that water can be heated without the use of additional equipment.

An additional layer of thermal insulation on the walls of the unit will prevent it from overheating.

Intuitive control: LCD display with indication of operating parameters, 5 buttons and temperature controls. Weight - 29 kg. The warranty period is 24 months. The model is current for 2021.

Specifications:

• Thermal power: 5.40 - 12 kW;
• Dimensions: 400x700x299 mm;
• Efficiency: 92%.

pros

• easy to install and operate;
• noise level: <36 dBA;
• holds the temperature without any complaints;
• can also operate on liquefied gas;
• heat exchanger service life: 15 years;
• functions of gas control, auto-ignition and overheating protection.

Minuses

• malfunctions in the heating system were noted.

Bosch Gaz 6000 W WBN 6000-18 C 18 kW

This model is designed specifically for Russian conditions, which means that the boiler is resistant to pressure changes (9-17 mbar) and network voltage (165-240 V), and is completely protected from freezing.

Easily and quickly heats an area of ​​180 sq.m. The water is heated in a plate heat exchanger, and little fuel is spent on its operation.

The main heat exchanger is made of high quality copper without impurities. There is a modulated fan and a gas valve seal sensor.

Circulation pump - built-in, three-stage.

The flame control electrode is ionization.

The heat exchanger is protected from overheating by an installed temperature limiter.

Display - LCD, with indication of operating parameters. The warranty period is 730 days. Weighs only 28 kg.

Specifications:

• Heating system power: 5.40 - 18 kW;
• Thermal load: 6 - 20 kW;
• Dimensions: 400x700x299 mm.

pros

• easy to use;
• it is easy to install;
• does not make noise during the process;
• high performance;
• you can connect external regulators (ON/OFF, Open-Therm);
• auto ignition;
• pump blocking protection;
• high-quality assembly.

Minuses

• The first launch is long.

Combustion chamber and smoke exhaust system

Dual-circuit gas heating systems are characterized by two design types:

• with an open combustion chamber;
• with a closed combustion chamber.

Boiler equipment with an open combustion chamber is low-performance due to the use of natural convection, and requires constant ventilation of the room. It is more suitable for small country houses.

Boilers with a closed combustion chamber are high-performance devices. They take in outside air to form a combustible mixture. This reduces the impact of the unit on the microclimate in the room where the device is installed.

Air is pumped by a special fan. Therefore, the devices are perfect for large and medium-sized residential premises with the need for domestic hot water.

A passive smoke exhaust system is unsafe, and therefore forced exhaust is widely used. Solutions with coaxial chimneys (of the “pipe-in-pipe” type) have also become widespread. This design simplifies the installation process. The coaxial pipe simultaneously takes in air and removes combustion products.

The best wall-mounted double-circuit gas boilers

Lemax PRIME-V32 32 kW

Compact boiler in a stylish white box and made from European components (Valmex, POLIDORO, SIT, NordGas, Bitron).

The top lining is easily removed. You can connect a room thermostat to it to adjust the temperature inside the house as accurately as possible.

You can heat it with natural gas, or you can switch to liquefied gas without any problems.

LCD display, intuitive operation.

Adapted to gas changes. Combustion products are removed through a chimney (separate or coaxial - at the user’s request).

The unification of units and components is high, the thermal insulation is continuous, thanks to which residents will be as comfortable as possible near the unit.

It works stably even in the event of a sharp decrease or increase in voltage (185 - 245 v).

Specifications:

• Power parameters: 6 - 18 kW;
• Efficiency: 92.5%;
• Warranty period: 2 years;
• WxHxD: 430x770x268 mm.

pros

• there is a remote control function using Android and IOS;
• double level of protection against pressure in the circuit;
• sensors and sensors are protected from corrosion and scale;
• does not buzz or rumble during operation;
• sufficient power level;
• reasonable price.

Minuses

• no protection against pump blocking;
• volatile

Vaillant turboTEC pro VUW 242/5-3 24 kW

German quality standards and high-tech equipment - all this is reflected in the described wall-mounted boiler.

Its cost is high, but the functionality is excellent: electronic ignition; built-in switching module for eBus interface; switch winter-summer; possibility of manual configuration; “smart” pressure control in the system.

The user can configure the unit manually, or can trust the well-coordinated automation, which will find faults, if anything happens, and calculate all the parameters.

The burner is made of high-strength chromium-nickel steel, heat-resistant and heat-resistant.

The heat exchanger is plate-type, flow-through. The display is liquid crystal, has a backlight and convenient buttons. Weighs 40 kg. The warranty is given for 900 days, the service life is 10 years.

Specifications:

• Boiler power: 24 kW;
• Load: 9.40 - 26.70 kW;
• Parameters: 440x800x338 mm.

pros

• protection against freezing, pump jamming and fan problems;
• powerful;
• high-quality assembly;
• you can connect a separate chimney;
• flame modulation.

Minuses

• price (about 100 thousand rubles);
• expensive components;
• the pump is noisy.
• problems with post-warranty service in the regions.

Protherm Panther 25 KTV (2015) 25 kW

You can’t call it cheap, but it’s easy to call it high quality . The heat exchanger is made of copper (no foreign impurities), the combustion chamber is closed.

There is gas control, a safety valve, protection against freezing and overheating of the unit.

If the installation is left idle for a long time, the pump will turn on and off on its own to avoid blocking.

Convenient electronic control and autonomous operation distinguish this unit from competitors in the same price niche.

A pressure gauge is installed to monitor the coolant pressure.

It is possible to connect additional elements: room remote controls, programmers, thermostats.

The electronic system significantly saves fuel and does not require the constant presence of a person nearby.

Flame modulation reduces fuel consumption (both natural and liquefied gas). The warranty is valid for 730 days.

Specifications:

• Power: 8.40 - 25 kW;
• Thermal load: 9.40 - 27.10 kW;
• Weight: 41 kg;
• Dimensions: 440x800x338 mm.

pros

• connection of external control;
• auto diagnostics;
• all necessary types of protection are installed;
• long warranty period.

Minuses

• Efficiency is average;
• It is impossible to connect a heated floor.

Which is better - convection or condensation?

First of all, it is necessary to understand the difference between the operation of one and another unit.:

• Convection - works on the usual principle of heat transfer. The coolant is heated due to the thermal energy released during fuel combustion.
• Condensing is a boiler that produces two-stage heating of the coolant. First, the OM receives a certain amount of thermal energy from the condensation of water vapor, which is contained in the exhaust combustion products. The partially heated coolant then enters the primary heat exchanger and is finally heated in the usual way.

The advantage of condensing boilers is the ability to reduce fuel consumption and, accordingly, reduce the heating intensity of the heat exchanger. Since the liquid has already received some heat, the burner operating mode can be reduced.

All this together allows you to increase the service life of the boiler components and parts and increase its efficiency. The efficiency of condensing boilers, declared by all manufacturers, is 107-109%, although in this case the usual marketing ploy takes place.

Such efficiency cannot exist by definition, but this is not the main problem . Condensing boilers are able to demonstrate proper efficiency only in low-temperature systems, where the degree of return heating is lower than the condensate temperature.

This is only possible if the difference between external and internal temperatures does not exceed 20°, which is simply impossible in Russian realities.

Therefore, you can choose a condensing boiler only in southern regions with warm winters.

NOTE!

The price of a condensing boiler is almost twice the cost of convection models of the same power. If operating conditions do not allow you to obtain the expected effect, you should refuse to purchase a condensing model.

The best floor-standing double-circuit gas boilers

Lemax Premium-30B 30 kW

If you need an inexpensive but powerful boiler, pay attention to this model . This is a non-volatile unit, which has both gas control and protection against abnormally high temperatures. The model is compact and takes up little space.

Its power is enough to create a comfortable, warm environment in a house with an area of ​​up to 300 sq.m., and that’s quite a lot!

Permitted fuel is natural gas . The primary heat exchanger is made of improved steel, the combustion chamber is open, and the assembly is of high quality.

Natural gas consumption - 3.5 cubic meters. m/hour . Weight - 88 kg. Efficiency - 90%. The maximum coolant temperature is 90 °C. Natural gas consumption - 3.5 cubic meters. m/hour.

Specifications:

• Dimensions (WxHxD): 556x961x470 mm;
• Chimney diameter: 130 mm;
• Warranty - 36 months.

pros

• affordable;
• there is a convenient thermometer;
• gas control function;
• powerful;
• reliable.

Minuses

• mechanical control only;
• It is prohibited to use liquefied gas.

Protherm Bear 30 KLZ 26 kW

Automatic boiler with two circuits. It will not only heat your home, but also heat water for household needs.

The volume of the storage boiler is 90 liters, the heat exchanger is made of cast iron, which means that it is not afraid of corrosion, acids and aggressive external environments, it will withstand high temperatures and will serve you faithfully for at least 40 years.

4 sections, 2-way heat exchanger . The weight of the unit is 155 kg. Coolant temperature - 45 - 85 °C.

Electric ignition is smooth, it is possible to install an additional fan to remove flue gases.

Manufacturer's warranty - 2 years. In case of abnormal temperatures it automatically turns off. There is pump blocking protection.

Specifications:

• Dimensions (WxHxD): 505x1385x730 mm;
• Thermal power - 18.20 - 26 kW;
• Thermal load - 20 - 28.50 kW.

pros

• you can use liquefied gas as fuel;
• electronic control;
• there is a built-in boiler;
• “smart” diagnostics;
• flame modulation"
• frost protection.

Minuses

• very heavy;
• no power-on indication;
• You cannot install a separate chimney.

Lemax Premium-20B 20 kW

A domestic development, which in terms of its mechanics is absolutely not inferior to foreign units.

It corresponds to the declared power, has good efficiency (90%), is made of inexpensive, but high-quality and durable steel.

The necessary functionality is installed: gas control, protection against excessive heating of the housing.

A non-volatile model that is not afraid of power surges and power outages.

The combustion chamber is open. Heated area - up to 200 sq.m. Gas connection pipe - 1/2″.

Max. water pressure in the heating circuit is 3 bar, in the DHW circuit - 6 bar . The permissible coolant temperature is 90 °C.

Specifications:

• Maximum thermal power: 20 kW;
• Dimensions: 556x961x470 mm;
• Warranty period: 36 months;
• Boiler weight: 83 kg.

pros

• affordable;
• non-volatile;
• compact dimensions;
• great guarantee.

Minuses

• cannot be connected to underfloor heating.

The best non-volatile double-circuit gas boilers

Lemax Premium-12.5B 12.5 kW

Trouble-free boilers with good automation and at an affordable price . It warms up a room of more than 100 square meters well.

The connection pipe for the circuit is convenient, heats the water well and quickly. The efficiency is almost 100%.

It works by burning gas, specifically methane . Ignites manually. The steel coolant is not afraid of deformation and impacts; it will last from 5 to 20 years.

Thanks to manual control, it is possible to save fuel . The control panel is reliable.

Install a thermometer to monitor the temperature in the boiler. There is overheat protection.

Specifications:

• Maximum thermal power: 12.50 kW;
• Max. coolant temperature: 90 °C;
• Natural gas consumption: 1.5 cubic meters m/hour.

pros

• independent from the electrical network;
• inexpensive;
• quickly heats the liquid;
• there is protection against overheating;
• there is gas control;
• thermometer.

Minuses

• uneconomical;
• large heat losses;
• there is no protection against pump blocking and flame modulation.

Lemax Premium-25B 25 kW

A fairly massive and large-sized boiler running on natural gas . Capable of dispensing approximately 7 liters of boiling water in 1 minute.

There is no connection to the network, ignition is done manually, the coolant works without a pump.

Material: steel.

It is durable, cheap and light in weight . You can set the basic parameters yourself.

If the water reaches high values, the boiler automatically turns off.

There is a function to turn off the gas in case of flame extinguishment. Efficiency - 90%, weight - 88 kg. Gas consumption is low. The heated area is large - 250 sq.m.

Specifications:

• Boiler dimensions: 556x961x470 mm;
• Warranty period: 36 months;
• Natural gas consumption: 3 cubic meters m/hour.

pros

• easy to operate;
• reasonable cost;
• reliable.

Minuses

• There are no weather electronics.

Lemax Premium-16B 16 kW

An inexpensive option, optimal in its characteristics, suitable for both an apartment and a country house with an area of ​​160 sq.m..

It does not depend on the power supply; overheat protection will disconnect the device from the network when the maximum allowed temperature is exceeded.

A sensitive sensor is installed to prevent gas leakage.

It is necessary to install the unit, observing the required distances from the walls. Open combustion chamber, efficiency - 90%.

The warranty period is set at 36 months . Fuel - methane. The boiler produces 5 liters of hot water per minute. Mechanical control.

Specifications:

• Parameters: 416x744x491 mm;
• Weight - 60 kg;
• Chimney diameter is 130 mm.

pros

• heats the room well;
• inexpensive in price;
• qualitative;
• practical;
• there is protection against flame extinction.

Minuses

• it is prohibited to use liquefied gas in this model;
• There is no room thermostat and pressure gauge.

Manufacturers of units

Today there is a fairly large list of manufacturers producing double-circuit gas boilers. Making a choice is quite difficult, since often in terms of characteristics there can be completely identical models, but at the same time very different in price. This is due to the quality of the components used and the assembly technology, which affects not only the efficiency of the entire system, but also the service life of the product.

It is also worth noting that when buying a product manufactured by a well-known company, you can be sure that the actual characteristics correspond to the declared ones. At the same time, such companies provide full and fast warranty and post-warranty service.

Conventionally, it is customary to divide the entire gas boiler market into three groups: Italian, German and others. The most well-established companies include the following heaters:

1. Vaillant (Vailant). A German company that has developed its own burner design, which has improved the reliability and performance of its products. Their boilers have excellent protection and are most often made of cast iron.
2. Protherm. It has been on the boiler sales market for more than twenty years. They produce inexpensive products of excellent quality with interesting designs.
3. Ferroli (Ferroli). This company from Italy constantly monitors new technologies, which it then implements into its products. The models they produce are reliable and easy to use, and their affordable price makes them the most popular manufacturers in the world.
4. Bosch (Bosch). This corporation has an entire division specifically dealing with heat and power issues. Although their products are not the cheapest, in terms of reliability they are the best company in Germany.
5. Rinnai (Rinnai). The models of the Japanese representative stand out for their functionality and high efficiency indicators. The engineers of this company developed a unique fan burner that regulates gas flow depending on the pressure in the system.
6. Buderus (Buderus). Combines well-known German quality with an affordable price. Economical fuel consumption, small size, unpretentiousness to the quality of the coolant attract buyers from all over the world.
7. Olympia (Olympia). The South Korean company pays special attention to equipment protection. Its designers have developed a unique double overheating protection system.

The best condensing double-circuit gas boilers

BAXI Duo-tec Compact 24 20 kV

The developers of the Duo-tec Compact series have successfully combined advanced technologies, ease of installation, and ease of operation in one model.

This is one of the best adaptive models, equipped with a super-modern burner (which is capable of pre-mixing air with gas), a very convenient control panel and a bunch of devices and functions (auto-ignition, pressure gauge, thermometer, etc.).

The specified service life is 10 years, which means that for a very long time you will not have to worry about the heating system of your home area.

Weighs 34 kg, compact and stylish in appearance model with internal filtration of incoming liquid, installed air vent and safety valve.

Specifications:

• Warranty: 2 years;
• Parameters: 400x700x299 mm;
• Power: 3.40 - 20 kW;
• Load: 3.50 - 20.60 kW.

pros

• external control can be connected;
• auto ignition;
• flame adjustment;
• pump blocking protection;
• Efficiency is above one hundred.

Minuses

• energy dependent;
• no built-in boiler.

Protherm Lynx18/25 MKV 18 kW

This boiler has almost all the necessary functionality: a convenient closed combustion chamber, an air vent, a safety valve.

Thanks to its small size and wall installation, the boiler takes up little space and saves space.

Thanks to the auto-diagnosis function, the user will find out what kind of malfunction has occurred (you just need to look at the table with codes), and flame control will not allow gas to escape into the room if the flame suddenly goes out.

The primary heat exchanger is made of aluminum (which is why it weighs so little).

The control panel is electronic . The efficiency percentage is high (more than 100). On the front of the case there is a backlit display and a thermometer.

The circulation pump and expansion tank are built-in.

The warranty period is 2 years.

Specifications:

• Power parameters: 5 - 18 kW;
• Thermal load: 5.10 - 18.40 kW;
• Dimensions: 390x700x280 mm.

pros

• connection of external control is allowed;
• auto ignition;
• the boiler is protected from freezing and excessively high temperatures;
• blocking protection is installed;
• flame modulation allows you to save fuel.

Minuses

• liquefied gas as a fuel is prohibited;
• energy dependent.

BAXI NUVOLA Duo-tec+ 16 12 kW

If you need a lot of hot water, this model is ideal . The new generation stainless steel burner allows pre-mixing of fuel with air.

The combustion system is adaptive. If the pressure drops (even to a level of 5 mbar), the rated power will be maintained.

The hot water output in the first 30 minutes is more than two hundred liters . Pump post-circulation, automatic bypass, filter installed at the cold water inlet.

The control panel is convenient, with a wide display.

The temperature can be regulated either by a person or automatically: you just need to set the necessary parameters. Fire control is ionization.

Specifications:

• Boiler power: 2.20 - 12 kW;
• Load: 2.30 - 12.40 kW;
• Warranty: 24 months.

pros

• excellent efficiency level: 105.8%;
• weather-compensated automation;
• digital indication of pressure and temperature;
• When the pressure drops, the electronic pressure gauge is activated.

Minuses

• no room thermostat;
• Expensive.

Design and principle of operation

Despite the fact that gas heating devices are distinguished by a wide variety of designs and technical solutions used, there are schemes that are most widespread and are used everywhere.

A typical double-circuit gas boiler includes the following elements:

• gas burner installed in the combustion chamber;
• primary heat exchanger through which the heating circuit coolant flows;
• secondary heat exchanger for heating water supplied from the tap;

• three-way valve;
• controls and automatic regulation;
• circulation pump.

In lightweight wall-mounted units, the heat exchanger is made of copper and its alloys. In heavy floor-standing devices, heat exchangers made of thick porous cast iron are often found.

The operating principle of a universal boiler is quite simple; its operation can be divided into two phases:

1. Operation in heating mode . The gas burner torch heats the heat exchanger, through which the coolant flows, which then enters the pipes and heating radiators. Typically, water or antifreeze is driven through the system by a circulation pump, which increases efficiency and reduces gas consumption.
2. Operation in heating mode for hot water supply . At the moment when the hot tap is opened, the control valve cuts off the coolant flow in the heating circuit and directs it in a small circle to the secondary heat exchanger. Cold tap water, flowing through heated channels, heats up and comes out of the tap at the desired temperature.

Thus, a typical double-circuit boiler cannot simultaneously heat a house and warm tap water. This is the main disadvantage of devices of this type.

Types of double-circuit gas boilers

• Condensing boiler - generates heat not only due to the fact that gas is burned inside, but also due to the effect of condensation of water vapor (it is formed as one of the combustion products). This is durable equipment with high efficiency.
• Non-volatile boiler - works in difficult conditions without electricity. Such devices last a long time, are easy to operate and save energy.
• Wall-mounted boilers require mounting on the wall, with a mandatory indentation from other equipment and furniture. They combine both a heating boiler and a water heater. Suitable for small houses (350-400 sq.m. area).
• A convection boiler differs from a condensing boiler in only one way - the more complex principle of heat accumulation.

Principle of operation

A double-circuit gas boiler can operate in two modes - heating and water heating. The boiler itself has two circuits through which the coolant moves. One of them - with a primary heat exchanger - works for heating, the second - with a plate heat exchanger - for preparing hot water. Switching occurs using a three-way valve.

The exact operating mode of a double-circuit boiler is specified by the manufacturer, but usually the heating operating mechanism is as follows:

• When the room temperature drops below a certain level, the automation transmits a signal to turn on the circulation pump. The coolant begins to move, creating a vacuum in the return pipeline. At the same time the burner turns on.
• As the coolant flows through the heat exchanger, it heats up, spreading heat throughout the system.
• Running around the radiators, it cools down and returns to the boiler inlet at a lower temperature.
• It is heated again by passing through the heat exchanger.
• When the set temperature is reached (there is control by the coolant temperature, there is control by the room temperature), the burner turns off, the coolant circulates for some time, adjusted by the circulation pump (post-circulation mode). When the heat exchanger temperature drops to a certain level, the circulation pump stops. The boiler does not operate as long as the temperature is within normal limits. As soon as it becomes 1°C below the set limit, the boiler turns on again.

  Different operating modes of double-circuit gas boilers

With some variations, this operating algorithm is repeated in different boilers. When heating water for domestic needs, everything happens approximately the same, only the signal to turn on the burner is the appearance of water flow in the circuit. That is, you open the hot water tap, the burner lights up. Only in this operating mode does the three-way valve switch and close the coolant inside the boiler. The hot coolant heats the secondary heat exchanger, and from it the running water is heated. Heating stops when the water overheats (when the threshold value is reached) or after the tap is closed. The burner goes out, the circulation pump runs until the heat exchanger cools down, then turns off.

How to choose the power of a gas boiler

Do not strive to buy a boiler with the highest power . Based on the number of boiling water collection points in your home: the more there are, the more power you need.

About a third (30-40%) is spent on heating, add to these data another 10-20% of inevitable heat losses.

The remainder should be enough to heat your house or apartment . Example: for a house with an area of ​​200 sq.m. and with one bathroom, a boiler with a power of 24 kW is sufficient.

Insulating your home will help avoid significant heat loss and save fuel.

Boiler power

One of the key points in choosing a heating boiler is determining the required power. If we approach this with full responsibility, it is necessary to consider the heat loss of each room, if we are talking about an apartment or a building as a whole, if the boiler is selected for heating a private house. The calculations take into account the materials of the walls, their thickness, the area of ​​windows and doors, the degree of their insulation, the presence/absence of an unheated room below/above, the type of roof and roofing material. Geographical location and a whole bunch of other factors are taken into account.

Such a calculation can be ordered from a specialized organization (at least in GorGaz or a design bureau), if desired, you can do it yourself, or you can take the path of least resistance - calculate based on average standards.

Where does the heat leave the house?

Based on the results of all calculations, a standard was derived: heating 10 square meters of area requires 1 kW of heating power. This standard is suitable for rooms with ceilings of 2.5 m, with walls with an average degree of thermal insulation. If your room falls into this category, divide the total area that needs to be heated by 10. You get the required boiler power. Then you can make adjustments - increase or decrease the resulting figure depending on real conditions. It is necessary to increase the power of the heating boiler in the following cases:

• The walls are made of material with high thermal conductivity and are not insulated. Brick and concrete fall into this category for sure, the rest - depending on the circumstances. If you are choosing a boiler for an apartment, you need to add power if the apartment is corner. For “internal” ones, heat loss through them is not so terrible.
• The windows have a large area and do not provide airtightness (old wooden frames).
• If the ceilings in the room are higher than 2.7 m.
• If in a private house the attic is not heated and poorly insulated.
• If the apartment is on the first or last floor.

The design power is reduced if the walls, roof, and floor are well insulated and energy-saving double-glazed windows are installed on the windows. The resulting figure will be the required boiler power. When searching for a suitable model, make sure that the maximum power of the unit is not less than your figure.

Operating principle of double-circuit boilers

In heating mode, the unit operates as follows: after the first switching on, the burner “warms up” for a long time, and having reached the required numbers, gas stops flowing into the boiler.

The coolant drives heat back and forth through the coolant, combustion products are removed from the system (either by a fan or independently).

In the heating mode of the water circuit, its operation begins with the turn of the tap. The three-way valve stops the heating circuit, the gas burner lights up (if it was turned off) and hot water starts flowing from the tap.

Operating principle and specifics

Many owners of gas equipment do not even think about how a double-circuit gas boiler actually works. They mistakenly believe that heating of water and the heating circuit occurs simultaneously. In reality, things don't look so rosy.

A double-circuit gas boiler cannot operate in two modes simultaneously, ensuring the operation of heating and hot water systems. This is confirmed by the presence of a three-way valve in its device

In normal mode, the boiler constantly operates only to heat the coolant circulating in the system. In this case, the switching frequency and intensity of the flame are controlled by a temperature sensor. Simultaneously with the burner, the circulation pump is started if the operation of the heating system is not based on the natural circulation of the coolant.

The space in the lower part of the wall-mounted boiler is intended for gas supply, cold water connection, as well as outlets for the DHW system and heating circuit

Essentially, when the coolant temperature reaches a predetermined value, the sensor sends a signal to reduce burner activity. Until the temperature drops to the set value, the boiler will be in passive mode. Then again a command is received from the automatic sensor to activate the fuel supply valve.