HOUSE HEATING 



405 



circulate in such large quantity. There is naturally some 

 friction between, and mixing of, the currents rising and 

 falling in the same tube. This can be eliminated by the use 



^ 7 



After University of Minnesota 



Fig. 310. Proper arrange- 

 ment for heating water 



After University of Minnesota 



Fig. 311. Use of two tubes causes the 

 water to flow more rapidly. 



of two tubes connected top and bottom as in Figure 311. 

 Heat may be applied just a little off the center and the circu- 

 lation will be up one side and down the other. With this 

 the circulation is more rapid and the tube may be smaller and 

 yet the heat transmission the same. 



Air circulates in the same manner as water, but not quite 

 so positively. Air will not circulate through a single pipe, 

 because the difference between the weight of hot and cold 

 air is too slight. It must have two pipes, a riser and a 

 return pipe. 



