102 



GENERAL SCIENCE 



73. Hot Air System. The hot air system is used 

 extensively. Many public institutions use it by having a 

 central heating plant and large hot air ducts leading to 

 the various buildings. These ducts are placed under- 

 ground and the air is forced through them by large fans 



Vent Flue 



Pure 



CIRCULATION OF AIR IN A SCHOOLROOM 



The foundation enclosure, F, is made air-tight, with the only exit 

 through the vent flue, N, in D. The enclosure, E, is shut off from F, but 

 communicates with the outside air which passes through the register, A, 

 over which is the heater. When a fire is started in the heater, the air 

 around it rises and the outdoor air enters through E. At the same time 

 the heat of the smoke warms the air in the vent flue through the partition, 

 X, and creates an upward draft from under the floor. With these two 

 drafts there is a continual circulation of the air in the room through A 

 and the small registers, R, R, R, R, and up the vent flue. 



run by engines or motors. Fans are also used in large 

 buildings where there is only one heating plant in the 

 basement. Small private houses can be heated by this 

 system without the use of a fan. The difference in the 

 temperature of the air outside and that at the furnace 

 in the basement is sufficient to insure the flow of air to 

 the various rooms. The air outside the house is cold 



