HOT WATER INSTALLATION 181 



culate the water the length may be materially 

 increased. 



The most commonly used size is i/^-inch, 

 and when the houses are much over 100 feet 

 in length two or more coils may be used, 

 each extending only a part of the length, and 

 having separate feed and return pipes. 



Expansion Tank. Water expands in 

 heating. It is necessary, therefore, to make 

 some provision to take care of the expan- 

 sion, in order that the pipes shall not burst 

 and to keep them full at all temperatures. 

 This is accomplished by connecting the sys- 

 tem with an expansion tank into which the 

 excess water will flow as it expands, and 

 from which it will flow back into the system 

 as it cools. It is placed at or above the high- 

 est point in the system, but it may be con- 

 nected with any part of the system or even 

 with the boiler. 



The size of tank required is directly 

 proportional to the volume of water con- 

 tained in the system and is determined by 

 the amount of expansion resulting from 

 heating. The following table adapted from 

 Kent shows the relative amount of expansion. 



