108 THE PRINCIPLES OF FLORICULTURE 



bench heating systems. However, the whole of the 

 radiation, or even the bulk of it, is seldom placed over- 

 head, although the mains are often carried overhead on 

 roof supports. The coils are fed at the far end of the 

 greenhouse, and all coils in the system are return coils. 

 This plan is much used in the Western States, but not 

 much used in the East. Its principal virtue is that a 

 deep pit is not necessary for the heater, and as there are 

 many sites where it is not possible or practicable to secure 

 a boiler cellar of reasonable depth, because water is near 

 the surface, or rock formation makes it too expensive to 

 excavate, this system is at times a matter of necessity. 

 The great objection to the overhead system of hot-water 

 heating is that it is difficult to heat the greenhouse evenly, 

 because the far end of the house is bound to be warmer 

 than the near end or that adjacent to the boiler cellar. 

 This is due to the fact that the coils are fed at the far 

 end and the fault is more noticeable in long than in short 

 houses. The most common and the simplest arrangement 

 of piping for hot-water is in coils of parallel lines under 

 the benches, these coils being vented at the high end, 

 which is at the far end of the greenhouse. The coils 

 may be either vented by air cocks, which should receive 

 regular attention, or by automatic air headers which 

 require no attention. The most even distribution of 

 temperature is procured by dividing the coils into an 

 equal number of flows and returns. 



" It has been mentioned that large pipes and small 

 pipes are used for hot-water heating. The large pipes 

 referred to are 3-J-inch cast iron pipes which are cast 

 in lengths of 9 feet and are caulked together by the 

 use of the rust joint. This joint is made by caulking 

 into the head of the socket of the pipe or fitting several 



