The customary method of calculating the amount of hot-water radiating surface required to warm a building is to allow so many superficial feet of radiating surface per thousand cubic feet of space in each room, hall, or corridor. Thus, in living-rooms (a dining-room, for instance), it is usual to allow 15 ft. of radiating surface per thousand cubic feet of space, and such a room measuring 15 ft. by 20 ft. by 12 ft. high - which would have 3,600 cub. ft. capacity - would need a radiator with 54 ft. of surface to it. Entrance halls need 20 ft. per 1,000, as practically all cold air enters here and should receive warmth before going farther. Bath-rooms, 20 ft. per 1,000: bedrooms, 10 ft. to 12 ft. per 1,000. These figures will give an idea of what will be needed for other purposes. They will afford a temperature of about 62' when there is a hard frost outside. The piping used is the " red steam " quality. This is stronger than gas or water pipe. Custom has decided that this is the quality of pipe to use, but except ill very high buildings such a thick pipe is not needed as regards its ability to resist pressure.

Boilers are made of 5/16in. and 3/8-in. iron, and capable of withstanding any ordinary pressure, but with high buildings the saddle boiler or any shape having large flat surfaces should be avoided, as the plates may bulge out.