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

(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.

 TABLE IV. Size of Riser. Square Feet of Radiating Surface. 1st Story 2d Story 3d Story 4th Story 5th Story 6th Story 1 30 55 65 75 85 95 1 1/4 60 90 110 125 140 160 1 1/2 100 140 165 185 210 240 2 200 275 375 425 500 2 1/4 350 475 3 550 &8226; 3 1/2 850