Heating, Ventilation and Lighting 



197 



for the loss by radiation from windows, doors and walls, take the difference in 

 temperature in degrees F. between the lowest outside temperature to be provided 

 for and the temperature at which the room is to be kept, and divide it by the 

 difference in degrees F. between the temperature of the heat pipes and the tempei- 

 ature at which the room is to be kept. Multiply the quotient thus obtained by the 

 number of square feet of glass plus the number of square yards of external wall 

 surface in the room, and the product will be the radiating surface required in square 

 feet. In this rule it is supposed that the external walls are of brick; if of wood, 

 they should be allowed for according to their air tightness and comparative 

 temperature. For the rough estimate, however, the straight rule is near enough. 



To understand the application of the above rules, suppose that we have 

 a room to be heated 

 by indirect steam; 

 that the amount of 

 air to be supplied 

 per hour, including 

 ventilation, is 5,000 

 cubic feet; that the 

 room is to be heated 

 to 70 F. in zero 

 weather; that the 

 temperature of the 

 radiators is 210 F.; 

 that the area of glass 

 is 30 square feet 

 and the area of the 

 external wall is 20 

 square yards then, 

 by the first rule we 



have: 5,000x70 divided by 12,500 equals 28, the number of square feet of 

 radiating surface required to heat the incoming air (or in the terms of the rule- 

 to replace the escaping air). 



By the second rule we have: T V<y x 30 plus 20 equals 25, the number of 

 square feet of radiating surface required to compensate for the loss of heat by 

 windows, doors and walls. 



Then the sum of the results of these two rules (28 plus 25 equals 53) is the 

 total amount of radiating surface in square feet required to heat the proposed 

 room to the proper temperature under the given conditions. 



As the temperature of the heating surface of a furnace is between 400 and 

 500, i square foot is usually taken as being equal to 6 square feet of steam 

 radiator, or equal to heating approximately 300 cubic feet of space. Therefore, 

 if a furnace be required to do the work as suggested in the above example, it will 

 take 6.63 square feet of radiating surface to perform the work. The above rule 

 for the furnace may be applied to the stove. 



Mantel in living room near St. David's, Pa. David K. Boyd, architect 



