210 



GREENHOUSES 



i ( ig. 109. Type of tubular boiler much used in green- 

 house heating 



tubular boilers and that it is much more dur- 

 able. As a rule users seem to be well satis- 

 fied with it. 



Steam and Hot-water Boilers. As usually 

 constructed, low-pressure steam boilers dif- 

 fer but little in construction from hot water 

 boilers. The essential difference is that in 

 steam boilers provision is made for a steam 

 chest or storage above the water line, while 

 in hot-water boilers the space between the 

 top of the tubes and the top of the boiler is 

 so small that there is no room for an adequate 

 steam storage. This is equivalent to saying 



