A back boiler is a device which is fitted to a residential heating stove or open fireplace to enable it to provide both room heat and domestic hot water or central heating. The device is a water filled heat exchanger enclosed at the rear of the burning chamber with a hot water output at the top of the chamber and a cold water feed at the bottom.
The back boiler is typically used with a gravity feed circuit to the hot water cylinder, with a vent or overflow to prevent excess pressure build up. It can also be connected to a series of radiators to provide central heating but requires an electrical pump to be fitted to circulate the hot water.
A back boiler can improve the efficiency of a stove by acting as a heat-sink and can also act as a method of extracting additional heat from the flue system which would otherwise have been lost. Manufacturers of stoves with back boilers quote efficiency figures of up to 80% on oil-fed models.