HEATING AND VENTILATION 



205 



water heating apparatus. But let us note that, after the 

 heat reaches the coils of pipe in the rooms above the 

 furnace, it is then given off into the room by radiation; 

 hence we call these coils of pipe radiators. 



A hot-water system (see Fig. 77) requires that there be 

 an open (expansion) tank at the 

 top, so that, if steam forms, it 

 may escape without bursting the 

 pipes. When it does form, it 

 causes "pounding" in the pipes, 

 but it should not form if the 

 furnace is properly controlled. 

 Hot-water systems have the ad- 

 vantage of supplying an "even" 

 heat; they also do not cause so 

 much dryness of the air as do 

 hot-air systems. 



Steam-heating plants are oper- 

 ated on the same principle as hot- 

 water plants, but they require a 

 boiler in which the water is trans- 

 formed to steam, and a pressure- 

 gauge which must be watched to 

 see that the proper amount of pressure is maintained. 

 They are preferred in the heating of large buildings, or in 

 the heating of several buildings by the same heating plant, 

 for the reason that heat can be transported through 

 pipes, for considerable distances, by means of steam more 

 successfully than by means of hot air or hot water. Why 

 is this so? 



Sometimes combinations of heating systems are used. 

 Thus the radiators of a hot-water or steam system may be 



FIG. 77. Diagram of a hot- 

 water system. 



