190 GREENHOUSES 



per square inch the following rule will be 

 found useful in determining the amount of 

 steam radiation required for a house when 

 the lowest outside temperature to be ex- 

 pected is not lower than zero. 



Divide the number of square feet of glass 

 and equivalent glass. 



By 9 to heat house to 40 degrees 



By 7 to heat house to 50 degrees 



By 6 to heat house to 60 degrees 



By 5 to. heat house to 70 degrees 



The quotient will' be the number of square feet of 



radiating surface required 



Size and Length of Coils. There is less 

 friction in steam than in hot-water heating, 

 and for this reason smaller pipes may be used 

 in the heating coils. They are seldom larger 

 than i%-inch, and 1%-inch is very commonly 

 used. Even i-inch pipe may be used in 

 comparatively short runs. Smaller pipes 

 may also be used in steam than in hot-water 

 heating, for the reason that the radiation per 

 square foot of surface is greater and there- 

 fore less surface is required. In other words, 

 an equal number of smaller pipes or a small- 

 er number of pipes of equal size may be used 

 in steam than in hot-water heating. Small 

 pipes furnish a greater amount of radiation 

 in comparison to their cubic capacity than 



