A schoolroom 63 ft. by 35 ft. by 22 ft. high has nearly 51,000 cub. ft. of space in it, which, with an ordinary area of window glass and good walls, can be heated by 9 ft. of 4-in. pipe per 1,000 cub. ft. of space. This will give 55° P. in very severe weather, and 60° F. at any other time. If 60° F. is required in severe weather, then 10ft. of 4-in. pipe per 1,000cub.ft. must be allowed. If 2-in. pipe is used, then double the length will be required. The advantage of 2 in. pipe is that 2 ft. of this only holds half the water that lft. of 4-in. does, and this means getting the heat up in half the time after lighting the fire. If radiators are used, the heat can be got up still more quickly, as they hold the least practical quantity of water tor a given radiating surface.