VENTILATION 355 



Heating by a hot-air furnace and by the indirect method of 

 steam heating necessarily involves the movement of air, and 

 therefore insures that the room will be ventilated. 



Forced ventilation is produced by forcing the air into a 

 building with a fan or blower. Such a fan operates by means 

 of the centrifugal force of a paddle wheel which sends the air 

 off the edge of the blades. 



Exhaust ventilation is that in which fans are placed at the 

 top of the house, or ventilating flue, thus lessening the pres- 

 sure within the building by producing a slight vacuum. 



400. Waste Products. The waste products of life and 

 industrial processes that interfere with indoor occupations are : 



(a) Carbon dioxide and moisture from the lungs and skins 

 of animals. 



(6) The products of combustion from lamps, gas burners, 

 and other artificial lights. 



(c) Gases that are the products of cooking and manufac- 

 turing processes. 



(d) Irritating and poisonous dusts and gases. 



The human body is constantly giving off heat, carbon 

 dioxide, and perspiration. The heat is due to the chemical 

 combination of the oxygen in the air we breathe with the 

 carbon of the body. The products formed are heat and car- 

 bon dioxide. The heat given off keeps the temperature of 

 the body at about 98 Ys F. As we are constantly breathing, 

 there is a continual supply of heat which would increase the 

 temperature of the body above normal, unless it were radi- 

 ated in this manner to the air and surroundi ^g objects. Some 

 of the heat is given off to the air in immediate contact with 

 the body, by conduction, and some is lost by evaporation and 

 perspiration. 



