forced hot-water system

Water heated in a boiler flows up to the radiators, where it releases its heat to the ambient air; the water then returns to the boiler to be reheated.

main return pipe

Pipe carrying cooled water to the boiler.

boiler

Device in which water is heated before being distributed to the radiators.

circulating pump

Device moving water throughout the network of pipes and radiators.

expansion tank

Reservoir for absorbing water expansion; it keeps the water pressure in the system steady.

main supply pipe

Pipe carrying the hot water to the radiators.

branch supply pipe

Pipe carrying the hot water to the radiators one floor above.

radiator

Device transferring heat obtained from the passage of hot water to the ambient air.

branch return pipe

Pipe carrying the cooled water to the main return pipe one floor below.