Gas can be used to heat large premises in two ways. The first is as a boiler in a standard central heating system, where the water is heated by the gas boiler, and then pumped to radiators or convector heaters all around the building. A relatively efficient system, this is widely used to provide both heat and hot water in the same way as a domestic central heating system.
A less widely used method is the gas fired warm air system. With this method individual gas fired heaters are sited at strategic locations throughout the building. The gas is fed into a fan chamber through an array of jets. When heat is required, a thermostat will operate, opening a solenoid valve. This allows the gas to flow into the fan chamber where it is ignited by a spark from a high voltage transformer. The air in the chamber is then very quickly warmed up by the flames, until it reaches a temperature at which another thermostat operates. This switches on a fan driven by an electric motor. The fan then drives the air out into the room through ventilation grilles, of which there can be many linked together with ducts. As the air is expelled, cool air is drawn into the chamber through inlet grilles. This is heated and the whole process starts again. Once the room is heated to the required temperature the thermostat will operate, closing the solenoid and stopping the gas from flowing and thus extinguishing the flame. The fan will then run on until the fan chamber is cool (usually for around five minutes or so) to prevent the fan chamber from overheating.
This system is very powerful and one heater can serve a large area. However, the fans are often quite large, and sometimes noisy, making them more suited to heating factories and warehouses than offices.
