348 



APPLIED SCIENCE 



boiler to radiators, where it gives off heat. The colder water, 

 which has already given off its heat, returns to the boiler to 

 become reheated. By the circulation of water, heat is con- 

 veyed from the boiler to the room. 

 The movement of the water is due 

 to the fact that hot water is 

 lighter, or in other words its 

 density is less, than cold water; 

 hence it will rise and more cold 

 water will come in to take its 

 place. This movement will con- 

 tinue so long as there is a differ- 

 ence in temperature in the system. 

 One sq. ft. of heating surface is 

 required for 30 to 60 cu. ft. of 

 space heated. 



FIG. 175. Hot-Water Heating air takes its 

 System. turn warmed. 



391. Air Circulation. The 



circulation and ventilation of the 

 air in a room is necessary in any 

 method of heating. Warmed air 

 rises to the top of a room and 

 the cooler air settles nearer the 

 floor. A steam radiator warms 

 the air directly in contact with it 

 and this air therefore rises. Cold 

 place and is in 

 The temperature 



of the air in the room gradually rises until the air, walls, 

 ceiling, and furniture or machines have all been warmed. A 

 certain amount of heat is lost through the walls, ceiling, and 

 windows, and there is always a leakage of cold air into a room 



