Wall-mounted boilers with two circuits, running on gas fuel, make it possible to provide hot water supply to radiators (one circuit) And taps (second circuit) Houses.
Gas boilers are most often used to heat private houses.
Features of wall-mounted gas boilers for heating a private house
The wall mounting method imposes special requirements on the devices:
- compact dimensions;
- light weight;
- simple control;
- modern design.
Often, boilers are mounted on the walls not in separate buildings, like floor-standing ones, but directly in the utility rooms of houses - for example, in the kitchen.
For this, boilers are made relatively small size with control panel on the front. The case has a rectangular shape, which makes it easier to fit the device into the interior of the room.
The meaning of the parameters, which options are reliable
Power- a key parameter that allows the boiler to produce the required amount of heat for heating and hot water supply (DHW).
It is of great importance when choosing a suitable model and is calculated according to the principle 1 kW per 10 sq. m.
But not a single boiler should operate at maximum power, otherwise it will quickly fail. Therefore, when calculating the boiler power parameter, add 20% stock.
That is, for a house whose area is 100 sq. m., suitable boiler with power 12 kW.
Attention! If the boiler is required for year-round use, then you need to select two-stage device or power controlled unit.
Camera type affects immediately a number of characteristics of the boiler. The combustion chamber closed type allows you to install the boiler in a limited space. The main thing is that it should be next to the outer wall of the building, through which the coaxial chimney used with a closed chamber is removed.
For combustion chamber open type it will be necessary to equip the chimney and ensure the flow of air into the room. Due to the closed system, the closed type has higher productivity and savings than the open type. But the device with a closed chamber is more expensive.
When choosing the type of fuel it is important to note that modern boilers are adapted to work as on natural, so on liquefied gas. But it will be an advantage if there is a gas pipeline at the installation site of the boiler, since it is cheaper, more convenient and safer. The characteristics of each device indicate what is the fuel consumption when operating on natural and liquefied gas. By default, the gas boiler is set to run on natural gas, so when switching to a liquefied unit, you will have to reconfigure it.
Gas boiler efficiency- an important parameter in terms of the ratio of the costs of the operation of the device and the results of its work. The optimal efficiency range for wall-mounted boilers can be considered 90—95%. With a low efficiency, more fuel is spent, and for a high efficiency, more expensive elements for the device are needed - for example, copper heat exchangers.
In wall-mounted double-circuit boilers are used heat exchangers copper and stainless steel. First transfer heat well second- more reliable in operation.
In the boiler can stand as a pair of m single-steel, and steel-steel heat exchangers. One is responsible for the heating circuit, the other for the hot water supply.
And there are also models of boilers with bithermic copper heat exchangers, the operation of which is organized according to the principle "pipe in a pipe".
Hot water supply- an important function of a double-circuit boiler. Therefore, when buying it, it is worth studying in the data sheet such an option as DHW performance. Usually the parameters are at what temperature And how many liters the boiler can heat. For houses where hot water from taps is used quite often, this moment plays an important role.
All these parameters must be taken into account in order to effectively use the gas boiler. At the same time, it is worth using its resource economically - for example, do not turn it on at maximum power for a long time. In case of regular care ( inspection once a year) and proper operation, the device can properly serve for a long time - on average up to 15 years. You can choose the appropriate option for a particular building by examining the rating of models. In it, the boilers are located as the coefficient of performance (COP) decreases.
Rating of the best models and manufacturers
Wolf CGG 1K 24
The gas boiler made in Germany has a maximum power 24 kW. It is enough to provide heat for a building with an area over 200 sq. m. The device has a closed type combustion chamber.
This involves the use of a coaxial chimney.
The use of a copper heat exchanger for the heating circuit and a steel heat exchanger for hot water supply allows for a stable supply of heat from the boiler to rooms and hot water taps.
At a temperature +35°C 8.6 l. The device occupies the first line of the rating due to its high efficiency - 93.0%. For other benefits Wolf CGG 1K 24 can be attributed to a small weight - 40 kg and noise level 38 dB. The device allows the consumption of natural gas and 2.8 cu. m. per hour and liquefied 2.1 kg per hour.
Baxi Luna 3 Comfort 240Fi
Made in Italy, the appliance is designed for power 25 kW. It is suitable for space heating over 200 sq. m. The device has a closed-type combustion chamber, with which a coaxial chimney is used. Work in the boiler two separate heat exchangers: copper and stainless steel.
Photo 1. Wall-mounted gas boiler Baxi Luna 3 Comfort 240 Fi. The device is installed on the wall and connected to the heating circuit.
DHW capacity at temperature +35°C is 10.2 l. By efficiency 92.9% Baxi Luna 3 Comfort 240Fi in second place, but some of its characteristics are higher than those of the leader. For example, the noise level is only 32 dB, and weight - 38 kg. However, the device has a slightly higher maximum consumption of natural gas - 2.84 cu. m. per hour, as well as liquefied - 2.12 kg per hour.
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Bosch ZWA 24 2K
This device is designed in Germany and manufactured in Turkey. Boiler power limit 22.00 kW. This is enough to heat the room about 200 sq. m. The boiler has an open combustion chamber, which implies the presence of a chimney and ventilation in the room. A feature of this model is a bithermic (pipe in pipe) copper heat exchanger, which makes the device more compact.
At a temperature +35°C DHW circuit performance corresponds to 9.8 l. Efficiency reaches 92.0% . According to this indicator Bosch ZWA 24 2K ranks third in the rankings. The natural gas consumption of the device is equal to 2.52 cu. m. per hour, and liquefied - 1.93 kg per hour. The weight of the boiler does not exceed 36 kg.
Photo 2. Wall-mounted gas boiler from the manufacturer Bosch model ZWA 24 2 R. At the bottom is the control panel.
Baxi Main 5 24F
The boiler is designed and manufactured in Italy. Its maximum power corresponds to 24.00 kW. This is enough to heat a room with a slightly larger area. 200 sq. m. The device has a closed combustion chamber, which implies the presence of a coaxial chimney. This boiler also has a bithermic copper heat exchanger, which increases its heat transfer.
At temperature indicator +35°C the performance of the DHW circuit of the device is equal to 9.8 l. Your place in the ranking Baxi Main 5 24F occupied due to lower efficiency than other devices - 90.6% . The device consumes natural gas within 2.78 cu. m. per hour, and liquefied 2.04 kg per hour.
Navien Deluxe 24K
The device is designed and manufactured in South Korea. Its power corresponds 24.00 kW, which allows you to provide heating for more than 200 sq. m. area of the room. The boiler has a closed type combustion chamber. It uses a coaxial chimney. The boiler has two stainless steel heat exchangers.
Photo 3. Gas boiler Navian Deluxe 24K. The top cover of the device is removed, its internal structure is visible.
At a temperature +35°C DHW capacity is 9.9 l. The boiler took its place in the rating due to efficiency 90.5% . The consumption of natural gas in the boiler is 2.58 cu. m., and liquefied - 2.15 kg per hour. The boiler weighs only 28 kg and has one of the smallest noise levels - 35 dB.
Baxi Nuvola 3 Comfort
The Italian-made brand offers a whole line of models, of which for a small house the best option can be called Baxi Nuvola 3 Comfort 240 i. The boiler is designed for power 24.40 kW. This is enough to heat up 200 sq. m. area of the room. An open combustion chamber involves a separate chimney and ventilation in the room.
Copper and steel heat exchangers work for heating and hot water circuits. At temperature indicator +35°C DHW capacity reaches 10 l. Your place in the rating boiler model Baxi Nuvola 3 Comfort 240 i occupied due to efficiency 90.3% . The consumption of natural gas at the device corresponds to 2.87 cu. m. per hour, and liquefied - 2.2 kg per hour.
We will understand the variety of gas boilers. What to ask the seller in the first place? And what will he try to "suck in"? What is it better for owners of private houses to refuse, and what to strive for?
Let's start choosing a boiler for the house by considering the insulation of the building. What is available already significantly influences the choice or needs to be changed.
What sellers sell that buyers shouldn't take
Having bought a “slightly different” gas boiler, homeowners then speak as follows.
- Most of all complaints subsequently causes savings on the reliability of the brand. Although breakdowns of gas boilers do not happen often, nevertheless, before buying it is worthwhile to figure out which manufacturers have been on the market for a long time, and what they are. What can be bought in a particular store? In terms of reliability, the products of the concerns of Germany, Italy, Slovenia, Japan and Korea are in the lead.
- The greatest criticism is caused by the savings in the creation of hot water supply based on a gas boiler. After all, you have to use hot water all the time. “It was necessary to pay a little extra and take this one .... with this…." It turned out not as convenient as we would like, and it is impossible to redo it.
- There are misunderstandings about saving on power when buying. It doesn’t happen often, but the complaints are the most important…
- Recently, owners of gas boilers have been complaining about overpayments for "super-new" technologies that turned out to be unprofitable. Even though it's not very important...
- There are mistakes in the fundamental choice - the best would not be a gas boiler at all, however, for some reason ....
When a gas boiler is not the best
Does the house have a basis for economical heating
Gas is getting more expensive and will continue to get more expensive, like all other energy sources. His waste will directly depend on the insulation of the house, which is also not cheap.
The better the insulation, the more expensive it is. The worse the insulation, the more expensive the heating will cost. Where is the golden mean? - what degree of insulation is required, and what heating power should be in order to keep the house warm?
The balance of this is determined by the design of the building, in which measures for insulation are prescribed, and hence the power of the gas boiler.
How to conduct an independent calculation of capacities
As a rough approximation, it is believed that the energy loss of a residential private house should not be more than 100 watts per square meter of heated area in the coldest month. This means that the building must be “well” insulated, and there are no frank drafts in it, i.e. ventilation under control.
And this also means that a gas boiler with a power of 1 kW / 10 sq. m. must heat the house so that it is warm in it, and if this does not happen, then it is necessary to look for and eliminate heat leaks, which in the end will turn out to be cheaper than buying additional boilers and radiators, and then burning a lot of gas.
Before going to the store for a gas boiler, it is advisable to bring the building into proper shape.
What power to choose
Gas boilers should not exceed the heat loss by much. Otherwise, a powerful burner will overheat the coolant too quickly and the boiler will constantly turn off - work in the frequent ignition mode. Yes, and overpaying for powerful equipment is useless. It is accepted that the power of the equipment should be reserved for 15% of the heat loss. But as a rule, hot water is also prepared from a gas boiler. Then the power reserve needs to be increased to 25%. Then, with a house area of 250 sq. m. and possible heat losses of 25 kW, the house must heat a 32 kW boiler, which must be applied.
By the way, self-calculation of heat loss is a waste of time. It is unlikely that the real humidity of the plaster, the real damage to the insulation in the attic by rodents (for example) and the actual area of shading the front window with a tree, with a normal wind rose ... so it is not recommended to invent in this regard.
What to look for when choosing a boiler
In addition to the brand and power, there are a couple of important nuances when choosing a gas boiler for the home. Firstly, already at the design stage, it is decided whether the boiler will be with an open or closed burner. This is fundamentally important, since units with different burners have completely different requirements for installation and operation.
Secondly, it is decided how many heating circuits should be in the boiler. Domestic water is heated in the second circuit. And you need to decide how exactly it will be prepared, how much it will be needed, and where the equipment will be placed. Further details…
Would an open burner work?
The burner of the closed type (forced ventilation) operates under the influence of a fan. The air is sucked in from the outside of the room through the same pipe through which the gases are removed. At the same time, it heats up. Wall-mounted compact units are equipped with such a system, which can be installed in any utility room that is not wet, and the pipe can be led out through the wall. This is a universal cheap and most common option. But floor boilers are also supplied with such a burner, with more advanced functionality ...
An open-type burner (atmospheric) is supplied with more powerful floor-standing boilers. They should only be installed in a separate furnace, made according to the rules, equipped with an air supply to supply air to the boiler. Smoke is removed through a high atmospheric chimney. Such boilers do not have power restrictions and are recommended for large houses. Extremely reliable, equipped with a cast-iron heat exchanger, etc…
Do I need a second heating circuit
There is always one circuit for the movement of liquid through a heat exchanger in a gas boiler - the heat carrier for heating is heated in it.
But there may be a second circuit - water will be heated in it for hot water supply at home (DHW). In practice, it turns out that the second circuit reduces the final price of equipment for hot water supply. But it also reduces comfort.
From the second circuit, water can flow directly to the tap. This is inconvenient, since at each opening the boiler will turn on, you have to wait until the hot water heats up and reaches ... Also, water can also enter the intermediate electric boiler, where it gradually cools down, and be heated by electricity - as a result, water is a little more expensive ...
Features of single-circuit
The single-circuit boiler is designed to work with an indirect heating boiler, in which energy from the heating medium is used for continuous heating of domestic water. With this option, there is always a lot of cheap water, since it can be constantly heated by the boiler, and the capacity of the boiler is not small. The recirculation system makes it possible to get hot water from the tap immediately when it is opened. It is possible to fill the bath very quickly (draining the boiler), even if the power of the boiler itself is not high. It is possible to get hot water…
But the price of equipment is more.
With one or two contours choose
The practical recommendation is reduced to a single-circuit boiler.
The price of an indirect heating boiler with a capacity of 150 - 200 liters is not small. It contains a spiral pipeline for heating from heating and this tank has a special coating. An additional pump is also installed, an expansion tank of the recirculation pipe .... But subsequent comfort is more important.
With a double-circuit boiler, you can immediately get hot water at the tap without any equipment, just connect the pipe from the tap to the outlet of the second circuit. It will be possible to gain more or less comfortably even a bath, unless of course the boiler power is from 20 kW. Having paid a little extra for an electric boiler up to 50 liters, you will get an order of magnitude greater comfort. And yet - is it worth it to save money and always give up an avalanche of hot water?
As a rule, a double-circuit boiler is an economical option, which entails certain inconveniences in the future.
How a condensing gas boiler works
There is a lot of water vapor in the hot gases that are formed during the combustion of fuel. This water can be seen dripping from the chimney. In condensing boilers, steam is converted into water at a secondary cold heat exchanger, which is then drained into the sewer. For the system to work, it is necessary that the heating return be as cold as possible, literally 30 degrees.
Condensing boilers are designed primarily for low-temperature heating, to work with underfloor heating and with radiators (floor convectors) up to 55 degrees. Then they develop their "monstrous" efficiency of 110 (!) Percent.
But they can also work in the usual high-temperature mode, when the coolant is heated to 70 - 80 degrees.
Is a condensing boiler useful?
In Europe, laws have been passed obliging the installation of condensing boilers - heat generators using the energy of the phase transition of water. This increases energy saving up to 15% and significantly improves the environment.
But our ordinary houses, in most cases, are not ready for such a turn of events. Firstly, the house must be heat-saving - not only insulated, but also equipped with modern ventilation, wastewater heat recuperators and a ventilation jet. Then low-temperature heating will not cope badly with our cold weather.
Also, the heating system itself should consist of a warm floor (preferably), and the area of \u200b\u200bthe radiators should be 20 to 30 percent more.
It turns out that all this together, at current gas prices, is not economically profitable. An expensive condensing boiler, together with its own heating system, will not pay for itself. In Europe, where the climate is much milder, and the price of gas is higher, this is extremely profitable.
Therefore, such boilers are not very popular with us.
What to choose for home
According to the degree of automation, according to the presence of protection, the lines of boilers for a private house of the same power from different leading manufacturers are similar in price. Therefore, "picking in the bells and whistles" is more likely to be a choice in favor of a particular brand or design.
When arranging a private heating system, the main issue is always the right choice of a gas boiler, because the comfort level of your family will directly depend on it in the future. There are a lot of models of boilers, the functionality is different for everyone and the purpose too. Therefore, if you decide to buy a gas heating boiler, it is worth studying in detail the main features of this equipment.
What information will help you make a choice?
Before heading to the store or opening the site's catalog, you should find out for yourself the main points that will facilitate your further choice. Decide for yourself what functionality you need and what you want to get as a result - high efficiency, ease of use or maximum savings. Make a list of the main requirements for yourself, it will help you quickly decide on the model of the boiler.
A variety of boiler equipment in terms of fuel combustion efficiency
The amount of money that you pay for gas consumption at the end of the month depends on the energy efficiency of boiler equipment, so the choice of one or another type of unit should be taken with the utmost attention.
According to the “boiler type” parameter, boilers can be divided into types that will directly affect the level of energy efficiency:
- Turbocharged.
- Convection.
In condensing devices, the heat exchanger is heated by gas combustion and heat transfer from flue gases and heat from steam condensation in flue gases. Such heat exchange is possible due to the special design of the heat exchanger.
In a turbocharged gas boiler, gas condensation does not occur, so the energy for heating comes only from the combustion of gas masses.
The choice of operating principle may depend on various factors. For example, some owners, in order to save money, use the boiler only to heat their homes, and it is more profitable for them to receive water from the central hot water system.
How fuel is ignited in boilers
There are 2 main types of gas ignition:
- Electronic.
The pieza in the boiler is arranged like the ignition system in a lighter - a button is pressed on the boiler body, causing a spark, which in turn ignites the fuel.
Forced removal of gas combustion waste occurs by means of a built-in fan, which expels smoke through a special outlet. If you are puzzled how to choose a gas boiler according to the type of thrust, you should start from where you live. If the ventilation in your home is good, and there is a chimney, you can safely install natural draft equipment. In such boilers, a closed-type working chamber is installed, which allows the boiler to be used in places where draft is broken.
Where to install the boiler - choose a gas boiler according to the installation method
According to the installation method, it is easy to choose, there are only two varieties:
- Wall mounted (up to 100 kW).
- Floor structures of high power.
When deciding which gas boiler to choose, you must know exactly what power you need, because a device with a power of up to 100 kW can be installed on the wall. Boilers with power ratings above 100 kW are usually heavier and will not fit in weight. Floor-standing units are more powerful and have large dimensions, but there are exceptions.
Gas boilers work with hazardous fuels, so they require increased attention from the user. A malfunction of the device can lead to fatal consequences (for example, an explosion). Therefore, the boiler system must work according to a well-established mechanism.
It is impossible to control such a system manually, therefore, automatic systems are used in the devices, which:
- Provide fuel ignition.
- They support the combustion process and control the dosage of fuel in the boiler.
- Control the level of traction.
- The fuel supply is switched on when the coolant temperature threshold drops.
- Turn off the fuel supply at the maximum coolant temperature.
Automation is also responsible for your safety - the slightest interruption of the system for it will become a signal to stop the gas supply.
According to the principle of operation, the automatic control system in the boiler can be electronic or mechanical. The classic mechanical control of a gas boiler occurs without electricity - this system is considered non-volatile. It is in such units that piezo ignition can be found.
The mechanical control unit operates only in three modes: ignition of the fuse, fuel supply mode, full shutdown mode. The amount of gas that is supplied in the fuel supply mode is controlled by the user in manual mode. In this case, minor errors are possible when setting the temperature, due to the specifics of the operation of mechanical components. In contrast to the electronic control of a gas boiler, the mechanical system is more crude, but it is much simpler in its principle of operation.
The electronic system does not require manual selection of the operating mode, everything is controlled by temperature sensors that determine when to open or close the gas supply. It is enough to enter data on the desired temperature regime into the programmer once, and forget about this issue for a long time. Some manufacturers produce gas boilers with Wi-Fi control, this makes them very convenient for operation in large farms or in factories.
Before choosing a gas heating boiler, you need to highlight the main advantages of each control system. The advantages of mechanical control include its low cost and independence from electricity. If you are looking for an inexpensive gas boiler with simple functionality, a model with mechanics is ideal for you.
Electronic control is, of course, the highest level of heating equipment. Such units control the microclimate in the room with great accuracy. Although electronics, unlike mechanics, depends on electricity, at the moment the problem is easily solved with the help of an uninterruptible power supply.
What fuel is used in gas boilers
You can find units that use two types of fuel:
- Gas boilers on natural gas (methane).
LPG boilers use propane-butane as fuel. Unlike natural gas, this product is easily transported. To date, there are still settlements and other settlements to which there is no gas pipeline. The use of liquefied fuel boilers for residents of remote settlements is the only option to ensure a comfortable microclimate in their home.
Liquefied fuel boilers are strictly forbidden to be used in conventional gas pipeline systems without conversion. They have a different design. At the same time, there are models that can be converted from natural gas to liquefied gas and vice versa.
The choice of a gas boiler for heating a house according to the properties of the heating element
It is the heat exchanger that is responsible for heating the circulating fluid, so the energy efficiency of the entire energy system as a whole depends on it.
All existing devices according to the material of the heat exchange element can be divided into 5 types:
- Apparatus with aluminum heat exchanger.
- Units with a copper heat exchanger.
- Cast iron models.
The popular ones include units with steel heat exchangers. This is due to the low cost of the material and its good ductility. But due to poor corrosion resistance, such heat exchangers require periodic replacement. Also, a metal device has a large volume and weight, respectively, more valuable energy is spent on heating it.
Boilers with aluminum heat exchangers are often referred to as the boilers of the future. Aluminum alloys do not corrode and are able to work in an aggressive environment. They have good heat transfer properties, have an increased durability of the structure.
Gas boilers with a copper heat exchanger are mostly of low power. This is due to the fact that copper is prone to rapid burnout at very high temperatures. But because of its unique heat transfer properties, it is still used in thermal equipment with certain temperature operating ranges.
Stainless steel is a good option as a replacement for conventional steel because stainless steel heat exchangers are completely resistant to corrosion. In terms of price, they do not differ much from steel heaters, but their service life is many times longer.
Gas boilers with a cast-iron heat exchanger are very durable. The material is practically not affected by corrosion, but many buyers refuse boilers with a cast-iron heat exchanger due to the complexity of operation. Cast iron is very sensitive to temperature changes.
How does smoke exit the system in gas boilers
On this basis, two varieties can be distinguished: a chimney and a chimneyless boiler (parapet or turbocharged).
A chimney gas boiler produces smoke exhaust through an atmospheric chimney. It has a natural attraction. Such devices usually provide for an open chamber.
In a parapet, turbocharged, or chimneyless boiler, combustion products are discharged through a special channel - a coaxial chimney. These are forced draft boilers.
Boilers with accessories
In addition to the classic models, there are more functional gas boilers on the market. For example, you can find a gas boiler model with a built-in circulation pump, the presence of which allows you not to install the pump separately in the system.
It is also worth considering boilers with built-in expansion tank. These units are mounted in heating systems where frequent pressure drops are possible. An additional tank acts as a compensator, and takes on all the loads.
Before choosing a gas boiler for a private house, make sure it has a three-way DHW valve. It provides a uniform distribution of fluid flows throughout the heating system. All gas boilers of the new standard are equipped with such a valve.
Popular European brands of heating equipment
When choosing heating equipment, consider the lines of boilers from brands such as Vaillant, Ariston Viessmann - these are well-known European manufacturers that produce the most functional boilers in the world, featuring good power performance and wide application possibilities. Also be sure to pay attention to Bosch gas boilers, which are famous for their high reliability. It is impossible not to appreciate the Protherm gas boilers from the famous Czech brand. They are very popular among buyers because of their classic design and affordable price.
Double-circuit gas boilers are a convenient way to solve the issue of heating and supplying a private house with hot water. They are easy to use, have the highest efficiency and reliability, the main thing is to choose a boiler that is suitable for its characteristics.
The functionality of double-circuit boilers is due to the features of their design. They are equipped with two heat exchange circuits, one of which heats the closed heating system, the second - water for household needs.
The heat carrier in the primary circuit is heated in the gas combustion chamber. Water for the DHW system is heated by the hot coolant from the primary circuit only at the time when you open a tap with warm water. At the same time, the valve built into the boiler shuts off the supply of coolant to the heating system.
Selection by types and parameters
Double-circuit gas boilers are presented on the market with a huge variety of models, and it is sometimes difficult to understand which one is better to choose. Therefore, for the right choice, you must clearly understand the characteristics you need.
These include:
- power, that is, the ability to effectively heat the desired area and heat a sufficient amount of water;
- boiler installation method - mounted (wall-mounted) or floor-mounted;
- type of combustion chamber, it can be open or closed;
- principle of operation - convection, requiring, or condensation, allowing the use of a coaxial chimney;
- degree of automation, type of ignition and the presence of protective functions;
- manufacturer and the degree of trust in him.
Power
It depends on this parameter whether the boiler is really capable of heating the house for a long time, efficiently and without overloads. A full-fledged heat engineering calculation, which is performed by service specialists, should take into account all the features of the structure:
- wall material and degree of thermal insulation;
- number and total area of windows;
- ceiling height;
- the presence of complex elements - bay windows, glazed heated terraces, greenhouses.
It is quite difficult to perform such a calculation on your own, therefore, a simpler method is usually used. It is enough to calculate the total area of heated premises, and then apply the formula:
P = S 100 / 1000.
where P is the required power, kW;
S - area in meters.
For a detached house with insufficient insulation, this figure is increased by 15% in temperate latitudes and by 30% in the northern regions.
So, for an apartment with an area of 120 square meters, the nominal power of the boiler is 12 kW, but for a private house built in the Moscow region, it is better to choose a power of at least 15 kW, and for a colder region - 20 kW. This will allow the boiler to work without overloads.
You should also pay attention to the performance of the DHW circuit. To calculate the consumption of hot water, you need to know the number of water points in a private house and the likelihood of their simultaneous operation. At the same time, a flow rate of 400 liters per hour (6.6 liters per minute) is taken for each point. If two or more points are turned on at the same time, this indicator must be increased by the calculated number of times.
The total capacity of the boiler, sufficient to heat a private house and provide it with hot water, is the sum of the capacity of the heating system and the capacity of the heat exchanger for hot water supply.Wall or floor?
The installation method of the boiler depends on its power.: models designed for heating a private house up to 200-250 square meters are usually available in wall-mounted versions. They are compact and do not exceed in size, they can be placed in any convenient place, for example, in the kitchen or in the bathroom.
Such boilers are designed for a hot water capacity of not more than 14 liters per minute and can simultaneously provide two points of water intake. To reduce losses, it is recommended to install them close to hot water consumers.
Boilers with a total power of more than 20 kW are usually floor-mounted. Their dimensions and weight are superior to wall models, and it is better to place them in a boiler room with an equipped supply and exhaust ventilation system. The requirements for a particular model depend not only on the size, but also on the principle of operation and the type of combustion chamber.
Combustion chamber - which is better?
Gas boilers can be equipped with an open or closed combustion chamber. They differ in the way air is supplied to the combustion zone. In an open chamber, air is sucked in from the volume of the room in which the boiler is installed.
Therefore, they can only be installed in a boiler room equipped with a window or forced ventilation, otherwise the air in the room will become unbreathable. In addition, to ensure stable draft and complete removal of flue gases for such a boiler, it is required with a height of the vertical part not less than that indicated in the passport.
The combustion chamber of the closed type allows you to install the boiler in any room of the house. In this case, a coaxial chimney is used to supply air and remove exhaust gases, consisting of two corrosion-resistant pipes located one inside the other. Flue gases exit through the inner pipe, and fresh air taken from the street enters through the space between the pipes.
At the same time, fresh air is recuperated (heated), which has a positive effect on the combustion process. The coaxial chimney can be brought out horizontally through the wall. Thrust in this case is provided by a built-in fan. Wall models usually have a closed combustion chamber, so they can be used not only for heating a house, but also in apartments. 
Principle of operation
According to the principle of heat removal, gas boilers can be convection and condensing. The difference lies in the fact that in convection, the coolant is heated in the combustion chamber, and in condensation, the heat obtained during the condensation of steam is additionally used.
The advantage of a condensing boiler is its high efficiency- up to 96%. But him minus - strict requirements for the design of the heating system: the temperature of the return water entering the heat exchanger must not exceed certain values, usually 60 ° C, which requires professional calculation and adjustment of the system and large expensive radiators. 
Energy dependence, degree of automation and type of ignition
The simplest models of gas boilers do not require an electrical connection. Their functionality, as a rule, is low - they have an open combustion chamber, require connection to a full-fledged vertical chimney, and their start-up is carried out only manually.
Modern models of gas boilers are connected to the mains, they are equipped with automation that allows them to work completely autonomously, without human intervention.
Two parameters important for usability:
- number of heating stages;
- ignition type.
The cheapest models are single-stage. In them, the heating process alternates with the standby mode. Upon reaching the set temperature, the boiler stops the combustion mode, and heating will start again only after the coolant has cooled to the lower allowable value. This can lead to uneven heating.
With two- and three-stage heating, the boiler automatically selects the combustion intensity depending on the set temperature, so that the coolant does not overheat and the room temperature remains stable. The price of such models is slightly higher.
Ignition type in gas boilers sometimes manual- using a piezoelectric element, or electronic- in models equipped with a control unit. Piezo ignition after shutdown requires manual start, the electronic one turns on itself after a break in the power supply or elimination of the emergency operation of the boiler.
Other convenient features built into the gas boiler help make its operation completely safe. Almost all modern models of boilers are equipped with them. Such functions include control of the flame, draft, gas flow and other modes of combustion and heating system.
You can find out by the codes that are reflected on the display of the electronic control unit, some models also allow you to connect a GSM notification system via SMS.
Famous brands and manufacturers
Focusing only on the equipment manufacturer is not entirely correct, since most companies have a wide range of models with a wide variety of functions. But buying gas equipment from an unknown manufacturer, even with high-quality assembly, carries a number of risks. That's why When choosing a manufacturer, you should pay attention to the following nuances:
- warranty period and period of use of equipment;
- the location of service centers where repairs or maintenance can be made;
- the ability to buy or order spare parts and consumables;