148 COMMERCIAL ROSE CULTURE 



going to waste up the chimney; in some cases this averages 30 

 per cent, while, under the best conditions, it is 12 per cent. 

 It is very important to always keep tubes and flues thoroughly 

 clean as the heat is then absorbed by the boiler instead of going 

 up the chimney to waste. The other source of waste is in 

 systems where cold water has to be often fed to the boilers; 

 where the water can be returned to the boilers hot without loss, 

 a great saving in coal is effected. 



Greenhouses are generally heated by low pressure steam 

 which means a pressure of less than 15 pounds per square inch. 

 This is the most economical form, as the relative volume of 

 steam decreases faster than the temperature increases as the 

 pressure rises. 



CARE OF THE BOILER 



Horizontal return tubular boilers are commonly used for 

 steam heating; these, when properly set in brick, will last for 

 years and give good results. The furnace is the space above the 

 grate where the fire lies. The fire sheet is the sheet or part of 

 the boiler directly over the fire. The ash pit is the space below 

 the grate and it is important to keep this cleaned out every day 

 or the accumulation of ashes will obstruct the passage of air 

 through the grate and also cause the burning out of the grate. 

 The bridge wall is the wall at the back end of the grate, in the 

 style of boiler we are considering. This wall is to keep the 

 coal from falling off the back part of the grate and to force the 

 flame up to the bottom of the boiler; also, when the doors are 

 opened to put on fresh fuel, it reduces the amount of cold air 

 that will be drawn in under the boiler back through the tubes 

 and up the chimney. 



The combustion chamber is the space back of the bridge 

 wall. All boilers should be provided with a blow-off pipe at 

 the bottom, which should be opened once or twice a week to 

 clean out any sediment which may accumulate. The safety or 



