io6 



GENERAL SCIENCE 



When the radiator is in the room, no provision is 

 usually made by the heating system for ventilation as 

 in the hot air system. The rooms have to be ventilated 

 by opening the windows or by air ducts which permit air 

 to enter under the radiators. 



What is known as the hot air and steam system com- 

 bined is sometimes used in large buildings. In this 

 combination the steam radiators are placed in the base- 

 ment and the cool, fresh air is forced over them and 

 into the rooms by large fans and the impure air removed 

 from the rooms by a fan, as in the hot air system. This 

 is sometimes called the indirect system of heating. 



75. Hot Water System. -- The hot water system is 

 very similar to the steam system except that the boiler 

 in the basement and the radiators in the rooms and 



the pipes leading to them 

 are all full of water, and a 

 pipe extends to an expan- 

 sion tank in the upper part 

 of the house. This tank 

 receives the overflow of 

 water due to expansion by 

 heating. There are pipes 

 leading from the boiler in 

 the basement to the radia- 

 tors, and a system of pipes 

 leading from the radiators 

 in the rooms to the bottom 

 of the boiler in the basement, and through these the 

 water flows from the radiators after it has cooled. 

 In this system of heating all three methods of transfer 

 of heat are used. The heat from the fire in the boiler 

 is carried through the metal of the boiler by con- 



HOT WATER HEATING SYSTEM 



