HOT WATER INSTALLATION 183 



grees is 1.04432 1.00025=0.04307, or a little 

 more than 4 per cent. It is customary to 

 make the expansion tank large enough to 

 hold 5 per cent, or a twentieth of the water 

 contained in the system, including the boil- 

 er. Thus, if the system contains 100 gal- 

 lons, the supply tank should be large enough 

 to hold a twentieth of that amount or 5 

 gallons. 



The capacity in gallons of a linear foot of 

 standard wrought pipe is shown in the fol- 

 lowing table. 



Size of pipe Capacity per 



diam. in inches linear foot 



1 0.1408 gallons 



\Y 4 0.0638 



\Y 2 0.0918 



2 0.1632 



2y 2 . 0.2550 



3 0.3672 



4 0.6528 



5 1.0200 " 



6 1.4690 



Pressure Systems. Water in an open 

 kettle cannot be heated above 212 degrees at 

 sea level. At that temperature it boils and 

 all further heat energy is expended in vapor- 

 izing the water. In an open hot-water heat- 

 ing system the same is true, except that the 



