We get the average elevation of the system by multiplying the square feet of radiation on each floor by the elevation above the heater, than adding these products together and dividing the same by the total radiation in the whole system. In the case shown in B the average elevation of the system would be

HOT WATER HEATER AND CONNECTIONS.

(100 X 30) + (50 X 20)+ (10 X 25) = 24.3 + feet,

100 + 50 + 25 and we must proportion the main riser the same as though the whole radiation were on the second floor. Looking in table IV we find for the second story that a 1 1/2 inch pipe will supply 140 square feet and a 2 inch pipe 275. . Probably a 1 1/2 inch pipe would be sufficient

Fig. 50.

Although the height of the stories varies in different buildings,

10 feet will be found sufficiently accurate for ordinary practice.