156 HORTICULTURIST'S RULE-BOOK. 



above that of the surrounding air, there should be 1 square foot 

 of radiating surface for 4 square feet of glass for hot- water heat- 

 ing, in which the maximum temperature of the water is main- 

 tained at 180 degrees ; there should be 1 square foot of radiating 

 surface for 5 square feet of glass for low-pressure (under 5 

 pounds) steam heating. These numbers are given somewhat 

 greater by some authorities, and there is no doubt that if the 

 house is not much exposed, these higher proportions will give 

 most satisfactory results. 



The following table gives more exact values for these quanti- 

 ties and will be found to accord with the best practice in heating 

 of greenhouses, either by steam or hot water. It is to be noted 

 that for steam at 5 pounds pressure the temperature will be 

 about 220 F. For steam at 10 pounds pressure, the tempera- 

 ture will be about 240 F. 



2. Size of Pipes connecting Radiating Surface and Boiler 

 or Heater. 



Various empirical rules have been given for proportioning 

 main-supply and return pipes, which have proved quite satis- 

 factory in practice. Mr. George A. Babcock gives the following 

 rule, which will be found very satisfactory for greenhouse heat- 

 ing, whether with low-pressure steam or with water : 



The diameter of main pipe leading to the radiating surface 

 should be equal in inches to 0.1 the square root of radiating 

 surface in square feet. The main pipes should not be less than 

 1 inches in diameter, return pipes for water heating the same 

 size as mains, and, for steam heating, one size less than mains, 

 but never less than | inch in diameter. The following table shows 

 the radiating surface supplied by various sizes of main pipe. 

 (II.) SIZE OF PIPES. RADIATING SURFACE SUPPLIED. 



l\ in 155 square feet. 



1 " . . . . S 225 " " 



2 " . . * . . r 400 " " 

 2| " . . ^ . . 620 " " 



3 . .... 900 " " 

 3| " . . . . . 1220 * " 



4 " . 1600 " " 



