HOT WATER 19 



constantly entering at E drives the. air heated by 6" through 

 pipes and ducts to the rooms to be heated. 



The metal pipes which convey the heated air from the 

 furnace to the ducts 

 are sometimes covered 

 with felt, asbestos, or 

 other non-conducting 

 material in order that 

 heat may not be lost 

 during transmission ; 

 the ducts which receive 

 the heated air from the 

 pipes are built in the 

 non-conducting walls 

 of the house, and hence 

 lose practically no heat. 

 The air which reaches 



halls and rooms is FIG. 13. A furnace. Pipes conduct hot air to the 



rooms. 



therefore warm, in 



spite of its long journey from the cellar. 



Not only houses are warmed by a central heating stove, 

 but whole communities sometimes depend upon a central 

 heating plant. In the latter case, pipes closely wrapped with 

 a non-conducting material carry steam long distances under- 

 ground to heat remote buildings. Overbrook and Radnor, 

 Pa., are towns in which such a system is used. 



10. Hot Water. The hot air which rises from furnaces often 

 carries with it disagreeable dust, and hence furnace heating 

 is being largely supplanted by hot-water heating (Fig. 14). 

 The real labor involved in the two types of heating is practi- 

 cally the same, since coal must be fed to the fire and ashes 

 must be removed, but the hot-water system has the advantages 

 of cleanliness and economy. After the water in the radiators 



