BOILERS, FUELS AND FLUES 215 



cured, and for localities subject to a tem- 

 perature of 20 degrees below zero, a boiler of 

 20 per cent, greater capacity should be se- 

 cured. 



The term horse-power, as applied to boil- 

 ers, represents the energy developed in evap- 

 orating 34.5 pounds of water per hour from 

 a.temperature of 212 degrees, or the develop- 

 ment of 33,317 B. T. U. per hour. Roughly, 

 a heating boiler will supply 100 square feet 

 of radiation for each horse-power which it 

 develops. 



Fig. 113. Altitude guage for hot 

 water boiler 



Boiler Accessories. It has already been 

 stated that a steam boiler may be used for 

 hot-water heating by simply changing the 

 fittings. When used for hot-water heating 



