166 GREENHOUSES 



Heating coils are made by joining several 

 pipes together by means of headers. The 

 hot water is conducted to the coils from the 

 boiler by means of a larger pipe known as 

 a flow pipe or feed pipe. It is returned to 

 the boiler by means of a return pipe. In 

 steam heating the coils are often so arranged 

 that the water formed from the condensed 

 steam returns to the boiler through the flow 

 or feed pipe, instead of through a separate 

 return pipe. 



