HEATING THE RANGE 113 



system of the same size, which are in turn considerably 

 smaller than those required for gravity hot-water systems. 

 Forced circulation of hot-water is, without doubt, the 

 ideal heating system for large ranges of greenhouses, 

 whether for private or commercial use. By this system 

 a mild heat, so much desired for plant culture, is obtained. 

 The system has a range of heat almost as great as a steam 

 plant. It is nearly as responsive and does not require 

 such large pipe for mains or connections as either steam 

 or hot- water. Neither does it require large pipe for 

 radiating surfaces, because it does not depend on a large 

 quantity of heated water to maintain the required tem- 

 peratures." 



86. Low pressure steam heating with gravity return. - 

 " The radiating surfaces in low pressure steam with 

 gravity returns are placed in the same general positions 

 as are hot-water radiating surfaces, that is, under benches 

 and on side walls. There are as many or more ways of 

 constructing and laying steam coils as there are of hot- 

 water coils. It is only necessary, however, to avoid 

 water pockets, or in other words, to secure a good, natural 

 drainage, i.e. by gravity of the water of condensation. 

 This is obtained by arranging the piping in proper size 

 and pitch. 



" There are two principal ways of arranging the coils ; 

 namely, under the benches and at the sides of the house. 

 One way is by converging the coils so that the steam and 

 return valves are at the same end of the house. The 

 pipes begin at one end of the house, a considerable dis- 

 tance apart, and pitch so that at the far end of the house 

 they approach each other very closely. The condensation 

 is then carried with the flow of steam, the pipes pitching 

 all the way. The other way is to carry the mains over- 



