HOT WATER INSTALLATION 177 



the smaller may be the supply pipe used. In 

 greenhouse heating, however, the height is 

 seldom very great, usually varying between 

 8 and 20 feet, so that the following rule of 

 thumb usually proves satisfactory. The flow 

 pipe should be one pipe size greater in dia- 

 meter (inches) than the square root of the 

 radiating surface of the coil (in square feet), 

 divided by 10. Applying this rule to the 



above problem we have V 500 -r-io=2. 24 

 The next pipe size is 2/4 inches but this is 

 so close to the estimated size that a 2/^-inch 

 pipe should be used to insure efficiency. 



The size of the main supply pipe from the 

 heater is determined in the same manner by 

 taking the sum of all the radiating surface 

 to be supplied. It is better to have one main 

 flow pipe leading from the boiler, from 

 which branches to the various coils may be 

 taken, than to have a flow pipe direct from 

 the boiler for each coil, though two or more 

 flow pipes may be taken off. The return 

 pipes should be of the same size as the flow 

 pipes. The flow pipe is taken from the top 

 of the boiler and the return pipe enters at 

 the bottom. 



In Fig. 94 is shown a diagram of a method 

 for piping a medium-sized house. In the dia- 



