GKEENHOUSE AND WIXDOW-GARDEN WORK. 155 



surface, the higher the economy, but the greater the first cost 

 of the heater. The usual practice is to employ 40 square feet of 

 heating surface to 1 of grate surface for hard coal, and 80 feet 

 of heating surface to 1 of grate surface for soft coal.* One 

 f tiot of heating surface in a steam boiler or in a hot-water heater 

 will supply heat for about 8 square feet of radiating surface, 

 under mean conditions. It will usually give a heater ample in 

 size for the work required, but if more radiating surface is added 

 it may in some instances prove to be small. The table following 

 gives more exact proportions. 

 To maintain the temperature of the greenhouse 70 degrees 



(I.) Table showing Relation of Glass Surface, Radiating 

 Surface, and Heating Surface, f 



* 25 per cent less for small upright heaters. 



t From Carpenter's work on Warming by Hot Water and Steam. 



