174 GREENHOUSES 



necessary to provide this amount. For ex- 

 ample, i linear foot of i^-inch pipe furnishes 

 about half a square foot of radiating surface. 

 Divide the number of square feet of radia- 

 tion required by the outside area of a linear 

 foot of pipe of the desired size. The result 

 will be the number of linear feet of pipe re- 

 quired. From this is subtracted the 

 amount of radiation supplied by the flow or 

 feed pipe and other fittings. 



The following table gives the radiating 

 area in square feet of a linear foot of pipe of 

 various sizes. 



Radiating surface of 

 Size of pipe 1 linear foot 



1/4 inch 0.27 square feet 



1 " 0.35 



iy 4 " 0.43 



\Y 2 " 0.49 



2 " 0.62 



2*/ 2 " .... 0.75 



3 " 0.91 



3^ " 1.05 



4 " 1.18 



For practical purposes the following gen- 

 eral rule will give approximately the 

 amount of radiating surface required. Divide 

 the number of square feet of glass and 



