70 GARDEN FARMING 



2. Find the amount of pipe by dividing the radiating surface by 

 the number of feet required per square foot of radiating surface, 

 as given in Table III. Do not use pipe less than i^ inches in 

 diameter for hot-water radiation, nor less than 1 1 inches for steam 

 radiation, except on short runs. 



3. Find the size of main pipes by Table II, using the size next 

 larger when the radiating surface comes between the figures given. 

 It is usually better to have several main and return pipes, and divide 

 the radiating surface in sections or coils, as shown in figure 21. 



FIG. 21. Arrangement of heating pipes for bottom heat 



Distribution of heating pipes in the greenhouse. In green- 

 house heating two systems of piping are used, so far as the dis- 

 tribution of heat is concerned, namely, so-called bottom heat 

 and top heat. Bottom heat is secured by placing the pipes beneath 

 the benches on which the plants are grown. This, of course, neces- 

 sitates the construction of raised benches which will carry soil from 

 4 to 6 inches deep, under which the pipes are arranged as shown 

 in figure 21. The second system of heating is called overhead 

 heating and is extensively employed in houses used for forcing 



