First the heart of the system is the boiler. There are various types of boilers and some of the main types are indicated below;
- Conventional flue boiler is where the flue is connected to a chimney and discharged usually at roof level. The boiler takes its combustion air from the room so it is important that there is a permanent opening to the out environment (there are special regulations dictating the area of the openings).
- Room sealed boilers are ventilated by ducting fresh air direct from outside to the boiler combustion chamber which is sealed from the room. This sort of boiler is best suited in a kitchen where there are kitchen extract fans operating and there is no risk of sucking in fumes through the flue.
- Other types of boiler can be provided in the form of back boilers and situated in a fireplace in the lounge. The boiler unit is ventilated using a conventional flue arrangement. The boiler heats water for the heating and hot water use. In the front of the boiler a separate gas fire is provided which heats the room.
- One of the latest types of boilers having a high efficiency is a condensing boiler. With this type of boiler additional heat is extracted from the warm flue gases which condense to a vapour. Efficiencies can be up to 20% greater than with other type of boilers. The down side on these boilers is that they are more expensive and often there is a plume of steam discharging at the flue terminal.
Boilers can be supplied in various combinations and can be used just to heat water which is then used to heat the building through radiators and then indirectly heat hot water for the basins and baths. The alternative is called a combination boiler which contains package control systems, pumps and facilities to provide water for domestic hot water use. This is often easier to install but can be more expensive to maintain especially if the boiler is no longer manufactured.