HEATING AND VENTILATION 



203 



various means are used; this conveyance may be by means 

 of currents of hot air, of hot water, or of steam. (It is 

 common to use the term furnace as applied to hot-air 

 plants only, but there is no real reason why the term should 

 be so restricted.) 



The hot-air type is the cheapest type of heating plant to 

 install, and has the further advantage of distributing heat 

 more rapidly than other 

 types. The chief ob- 

 jections to it are that 

 it may also distribute 

 dust, and that it may 

 cause the air to become 

 too dry to be comfort- 

 able. This latter ob- 

 jection may be con- 

 siderably offset by 

 keeping large pans of 

 water under the reg- 

 isters through which 

 the hot air comes into 

 the rooms. You should 

 remember that as air heats and expands it increases in 

 power to absorb moisture. So, whatever heating system 

 is used, provision needs to be made for keeping the air 

 moist enough to be comfortable. 



By studying Fig. 75 you can see how a hot-air furnace 

 works. However, it is not quite as simple a matter as it 

 seems. For one thing, there must be careful figuring to 

 insure that enough fresh air enters the furnace to feed the 

 hot-air pipes that lead away from it. You will note in 

 the figure that only one cold-air flue enters the chamber 



FIG. 75. Diagram showing how a hot-air fur- 

 nace works. After MILLIKAN and GAI.E. 



