344 



APPLIED SCIENCE 



The double-pipe system requires greater length of piping, but 

 the single-pipe system requires larger piping, so as to allow 



the condensed water to 

 return to the boiler while 

 the steam is ascending 

 the pipe. 



385. Indirect Meth- 

 od. The indirect method 

 of heating (Fig. 174) is 

 the more effective system 

 for large buildings and 

 schools. The heater is 

 generally placed in a 

 cellar or basement. The 

 air is passed over its sur- 

 face of pipes, and is then 

 directed by a distributing 

 system of sheet iron or tin 

 pipes up into the rooms 

 to be warmed. Heating 

 has the effect of circulat- 

 ing the air in the conduct- 

 ing pipes. The air may, 

 too, be forced into the cir- 

 culating pipes by a blower 

 or fan located in the cel- 

 lar. The well-known hot- 



FIG. 173. Steam Heating System. 

 air furnace is an example of the indirect method of heating. 



386. Advantages and Disadvantages of the Indirect 

 Method. One great advantage of the indirect system is that 



