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

Recommendation points

• The main differences between the parapet boiler
• Features and benefits of installation
• Heat exchanger – what should be the heart of the boiler
• Do I need an additional circuit
• Connection diagram
• Heat output and energy efficiency
• Automation used

Gas boilers will be used as the main heating unit for a long time. We will tell you what is the point of installing parapet-type equipment in a private house, what is the principle of its operation, the benefits of use and disadvantages, and most importantly – how to choose the right model yourself.

The main differences between the parapet boiler

The removal of combustion products in conventional boilers occurs through a chimney, which is not provided in every home. Parapet boilers are distinguished by an insulated combustion chamber, two-way communication of the boiler with the outside environment is carried out through the outer wall of the building. Most wall-mounted gas boilers are parapet.

The benefit of this design lies not only in the simplified installation. Since the firebox does not communicate with the internal environment, gas leakage is possible only at the connections of the gas-conducting channels, which are easily accessible for inspection and replacement. There is also no need to normalize the air flow: the boiler receives the oxygen necessary for combustion from the outside, without drawing warm air from the house.

The model range of mounted parapet boilers is very wide. These can be both the simplest units with one heat exchanger and mechanical automation, and complexes stuffed with electronics, including a closed expansion tank, and a circulation pump, and a digital power adjustment circuit.

Features and benefits of installation

Installing the boiler in a hinged way is easier and cheaper. There is no need to arrange shut-off screens, to strengthen the platform for a massive floor boiler, to optimize the supply of communications. Hinged boilers provide a significant increase in free space in the boiler room, and in some cases they can be installed not in technical rooms. But there are a number of reasons to abandon the hinged installation..

Arrangement of a parapet gas boiler: 1 – external wall of the house; 2 – heat exchanger; 3 – heating agent outlet; 4 – temperature sensor; 5 – piezo ignition; 6 – control handle; 7 – gas valve; 8 – gas supply; 9 – heating agent inlet; 10 – pilot burner; 11 – burner; 12 – air inlet from the street; 13 – exhaust gas outlet

The main reason is that such boilers do not heat the space around them. If the floor technology has a convection casing and, due to the heat of the combustion chamber, is capable of heating a room of 30-50 m³, then attachments require the installation of an additional radiator. This is important when installed in a hallway or, for example, in a kitchen.

There is also a power limitation. Due to the design features, mounted boilers are lightweight, but at the same time they are very sensitive to abnormal operating modes, in particular, to overheating. The higher the power of the gas flame, the more probable the breakdown of the heat exchanger, therefore, with a calculated heating power of over 30-40 kW, preference should be given either to floor-standing units with a steel or cast-iron heat exchanger, or to an expensive boiler with increased reliability with a guarantee of at least 10 years.

As for installation, its main difficulty lies not in the process of mounting, but in the need to install a deflector on the facade and conduct a coaxial chimney through the wall. The installation scheme has only three stages:

1. Hole through a wall with a suitable casing diameter.
2. Hitching up the indoor unit with two or four anchor bolts.
3. Inserting and securing a chimney with a deflector.

In most cases, wall-mounted boilers are placed on the leeward side of the building, or where the deflector will not disturb the appearance of the facade.

Heat exchanger – what should be the heart of the boiler

Actually, the heat exchanger itself in most wall-mounted boilers is copper, less often – steel. Hinged-type cast iron boilers are an absolute rarity, mainly heating columns for industrial heating systems.

Copper heat exchangers have many thin passages, which provide two of their main advantages. The first is the small volume of the coolant, which heats up quickly due to the small wall thickness. The second plus is a highly branched coil circuit and the presence of additional radiators, which gives a gain in the total area of ​​the heated surface.

The main disadvantage of copper heat exchangers is the high requirements for the circulation rate, gas quality and coolant preparation. Carbon deposits, soot, oxide layers, scale deposits on the inner walls – all this greatly impairs heat transfer. Note that the burners of such boilers have a special device and are designed for economical combustion of gas in accordance with the current required power, which is why gas equipment requires rather fine adjustment..

For this reason, unfortunately, many imported boilers simply refuse to work when connected to the local gas supply network: either the pressure does not correspond to the passport, or the composition of the combustion products confuses capricious electronics. And finding a specialist with the necessary qualifications to set up and maintain such equipment is problematic, especially in remote regions..

Steel heat exchangers can be flushed together with the rest of the system with the same composition, while copper heat exchangers need to be flushed individually. The main advantage of “black” heat exchangers is their durability, because a similar product can burn out or collapse only due to a factory defect, the only problem is corrosion and scale deposits. But there are other nuances: welded heat exchangers are not reliable enough, products from one-piece seamless pipes molded by cold stamping recommend themselves much better..

Do I need an additional circuit

There can be several heat exchangers in the boiler: both for direct use and for secondary heating of water. In order to rationalize fuel consumption, manufacturers are trying to ensure the most complete absorption of heat from a gas flame by placing several heat exchangers in series in different temperature zones of the combustion chamber. This is how, for example, condensing boilers are arranged, having one of the highest efficiency – about 95%.

Combined heat exchanger

The second circuit can participate both in direct heating of water, and be looped-back with an additional boiler. The efficiency of heating in the second circuit is highly dependent on the current operating mode of the boiler. Boilers with a copper heat exchanger are designed for a dynamic mode of operation, because they have almost no inertia.

If the system is currently cooling down, then the water will come in lukewarm, especially at high flow rates. Equipment with a burner for individual heating of an additional circuit is more expensive to purchase and maintain. It is more reasonable to provide preheating with the second circuit, and make accurate adjustments with a gas column or electric flow.

Double-circuit heat exchanger

Please note that the secondary heat exchanger channels are quite thin and more prone to deposits. It is better to prefer heat exchangers of an uncombined type of indirect heating, in which case, if the second circuit breaks down, it simply turns off, and the boiler continues to work exclusively for heating until repairs are performed.

Connection diagram

If for floor-standing boilers there is freedom to choose the side of the pipe supply, then wall-mounted boilers have mainly a bottom connection to all communications. This is convenient when the boiler needs to be neatly fit into the interior, but without the built-in circulation pump and expansion tank, the piping sometimes becomes rather cumbersome and inconvenient for maintenance.

An example of a connection diagram for a parapet gas boiler: 1 – wall-mounted gas boiler; 2 – security group; 3 – heating radiators; 4 – expansion tank; 5 – circulation pump

Although the piping scheme for the parapet boiler does not have key differences from the chimney modifications, it must be planned in advance along with the layout of the boiler room. Since the parapet boiler practically does not impose requirements for fire safety, it is convenient to close the supply of communications and piping with a decorative box, including from gypsum plasterboards with inspection hatches.

Heat output and energy efficiency

Of course, when choosing a boiler, priority is given to the ability of the unit to replenish the dissipation capacity of the radiators. When calculating, three main factors must be taken into account: heat loss during transportation of the coolant, boiler efficiency and energy consumption of the combustion gas.

As we have already said, condensing boilers are considered the most energy efficient, with a small margin behind them technology with a copper heat exchanger and an efficiency ceiling of about 92–94%. The least economical are tubular steel heat exchangers without a condensation circuit, they already have tangible inertia and efficiency up to 90-93%.

Automation used

In conclusion, let’s briefly touch on the types of automation. The most simple thermostat of the mechanical principle is completed with most of the heating equipment of domestic production: “ROSS”, “Aton”, “Danko” and others like them. Basically, automatic equipment manufactured by SIT (Italy) or MM (Germany) with built-in piezo ignition is installed.

Imported heating equipment (Hermann, Grundfos, Ferroli) has a volatile electronic circuit for automation and power adjustment, which requires voltage stabilization and sometimes uninterruptible power supply. Most of such equipment already includes all the necessary piping and can be directly connected to the heating system according to the simplest scheme.