A gas boiler is a high-tech appliance consisting of three main units:
The different models of gas boilers can be equipped with extra devices guaranteeing their safety:
Gas boilers have maximum and minimum rated power that should be taken into consideration with heating installation needs.
- conventional gas boilers. The energy from fuel combustion is not completely used and the so called latent heat is lost by being discharged together with the vapors through the chimney. This is the older type of gas boilers where the gas consumption is much higher. According to the ЕС Directive for Ecodesign of 2015 the distribution of conventional gas boilers has been banned.
- condensing gas boilers. This is a very economic and profitable heating device that stands out with its very high efficiency, as its coefficient of efficiency can get up to 25% greater than the conventional gas boilers. In this type of gas boilers, not only the heat generated from fuel combustion but also the residual energy from the condensation (the water vapor that forms during combustion) is utilized. The water vapor from the combustion condenses and is discharged from the system via special drainage line to prevent any exposure of the system components to the effects of acidic aggressive condensed matter. Due to the lower operating temperatures, this type of gas boilers have longer service life.
Wall-mounted, floor-standing and rail-mounted. Wall-mounted gas boilers are the preferred heating solution for medium-size living quarters and offices. They are much cheaper and easier to install than the other types of gas boilers.
– system (single loop) gas boilers. It is used only for heating. Water is heated in an on-demand heat exchanger. Domestic hot water can be heated indirectly by adding an extra hot water storage tank.
- combination (double loop) gas boilers. It may be used for both central heating and domestic hot water. This type of gas boilers supply heating power directly to the central heating system of the place – underfloor heating system or wall-mounted radiators, whereas the second loop supplies domestic hot water on demand. The combi condensing gas boiler is the most commonly used and sold type of gas boiler.
- ignition by piezoelectric element. The gas boiler burner is ignited by manually pressing a button.
- electronic ignition. The ignition of this type of gas boilers starts automatically. The advantage of this type of ignition is that gas boilers can be automatically switched on and off in case of power failure. Gas boilers with electronic ignition are more saving as they do not require the presence of a continuous flame.
– gas boilers with natural draught system (the fireplace type). This type of gas boilers have an open combustion chamber. All that is needed is a good natural ventilation and aeration while the products from combustion are discharged through the chimney.
- gas boilers with forced draught system (the turbo type). This is the preferred type of gas boilers available on the market. The flue gases are discharged by an built-in fan on the top of gas boiler. They are the perfect solution for premises without a chimney, the only thing that needs to be done is to make an opening in the wall, which saves money on installation.
- burner with ambient air. The combustion process uses ambient air and the mixing takes place directly in the combustion chamber,
- burner with pre-fixed mixture Premix type. Air is fed through an electronic-controlled fan and the mixture and combustion take place in a pre-determined amount. The combustion process in this type of gas boilers is automated and the combustion proceeds evenly, avoiding the formation of high temperature spots.
– open system gas boiler. The oxygen from ambient air penetrates the chamber through special purpose channels and ensures the combustion process. Flue gases are discharged to the environment through the chimney. The premises must be provided with natural fresh air ventilation through a window to let out the combustion products and to prevent the accumulation of carbon monoxide.
- closed system gas boiler. It is a closed area with the burner inside where the air is let out through a coaxial flue system. It is used in premises without a conventional chimney. On top of the boiler there is a fan to discharge the flue gases. Some models have the option to install 2 separate flue pipes - one for air intake and one for flue gases. In both cases flue pipes need to made of plastic (polypropylene pipes) or stainless steel of at least grade AISI 304 in order to withstand the contents of the flue gas and condensation.
The heat exchanger is an important component of the gas boiler installation. It can be made of different materials such as copper, steel, aluminium alloy and less commonly cast iron:
- steel. No cracks will form upon the contact of such heat exchanger with high temperatures (especially when close to the burner) thanks to the steel plasticity. They are cheap thanks to the simplicity of steel treatment. This type of heat exchangers are apt for corrosion. The rust formation both inside and outside can lead to shorter service life. Due to their big dimensions and heavy weight, they have higher gas consumption.
- cast iron. This is the second most popular heat exchanger. Unlike steel, cast iron is not that apt for corrosion but it is quite brittle. Cracks may appear if it is heated unevenly, which is why they need regular maintenance and prevention.
- copper. The gas boilers with copper-made heat exchanger are light but durable, remarkable for their small dimensions and rust-proof property. A disadvantage can be their expensive price.
- aluminium. Low weight, high plasticity and possibility to make structures of any shape and complexity. Corrosion resistance, high chemical resistance and perfect thermal conductivity.
Types of gas boilers based on: