HOT WATER INSTALLATION 173 



we have 220 or the number of B. T. U. given 

 off by each square foot of radiating surface 

 per hour. If, then, we divide 600,000 by 

 220 we have 2,727 which is the number of 

 square feet of radiating surface to be pro- 

 vided. 



These principles may be embodied in the 

 following formula where R the amount of 

 radiating surface required in square feet; T, 

 the temperature to be maintained inside the 

 house; t, the lowest outside temperature to 

 be expected; and G, the number of square 

 feet of glass and equivalent glass. 



R= (T-t) * G 



(160-T) 2 



This formula gives a wide margin of safe- 

 ty. Most builders prefer to use consider- 

 ably less radiating surface and depend on 

 forcing the furnace in extremely cold 

 weather. By so doing the temperature of 

 the coils may be kept at 180 degrees or even 

 considerably higher under favorable condi- 

 tions and the amount of radiation required 

 will be correspondingly less. 



Amount of Pipe Required. Having esti- 

 mated the amount of radiation required the 

 next problem is to find the quantity of pipe 



