HOT WATER INSTALLATION 169 



boiler and w^the weight of a cubic foot of 

 water when it enters the boiler. 



This, of course, disregards friction. The 

 practical application is that when it is de- 

 sired to increase the velocity of the water; 

 e.g. in long runs, it may be done by either 

 lowering the boiler or by raising the height 

 of the flow pipes. 



The following table shows the velocity in 

 feet per second in a hot water system under 

 various conditions. 



Height Difference in temperature on leaving and 



of entering boiler 



Column 5 10 15 20 30 40 



Feet per second 



5 ft. 0.541 0.750 0.922 1.09 1.33 1.51 



10 " 0.765 1.06 1.32 1.55 1.88 2.04 



20 " 1.085 1.50 1.85 2.19 2.66 3.01 



30 " 1.35 1.83 2.26 2.68 3.26 3.71 



Arrangement of Piping. There are two 

 approved methods of arranging the piping 

 for hot-water heating. One is known as the 

 "down hill"; the other as the "up hill." In the 

 former the highest point in the system is 

 directly above the boiler. In the latter the 

 highest point is at the end of the system 

 farthest from the boiler. Either is satisfac- 

 tory and is preferred to the "level" system 

 sometimes advocated. In either the "down 



