HOT WATER INSTALLATION 175 

 equivalent glass : 



By 6 to heat the house to 40 degrees 

 By 4 to heat the house to 50 degrees 

 By 3.5 to heat the house to 60 degrees 

 By 3 to heat the house to 70 degrees 



The quotient will be the square feet of 

 radiating surface required. 



Size of Flow Pipe. Having determined 

 the amount of radiation necessary, the next 

 problem is to determine the size of the flow 

 or feed pipe required to supply the coils. 

 Experience has shown that it is not necessary 

 for the supply pipe to be equal in capacity 

 to the sum of the capacities of the coil pipes. 

 The correct size may be determined, theo- 

 retically, by the use of the following rather 

 tedious formula: 



A- HR 



25wvt 



In this formula A=the cross section 

 area in square inches of the flow pipe; 

 H, the total radiation in B. T. U. per 

 hour given off by the coils ; R, the radiating 

 surface in square feet; w, the weight of the 

 water per cubic foot; v, the velocity of feet 

 per second; t, the difference in temperature 

 between the water when it leaves the boiler 

 and when it returns. 



This formula is seldom used but the fol- 



