Chimneys are proportioned either to the amount of radiating surface in a building, or to the horsepower required for machinery, or to both combined. The draft pressure increases with the height of the chimney. Boilers operating under forced draft from fans or blowers do not require high chimneys, except for the purpose of conveying the gases of combustion above the breathing zone. But in all ordinary buildings the chimneys should be built sufficiently high and large so that forced draft is not necessary.

Size Of Chimney For Given Amount Of Radiation, Or Horsepower

Steam Radiation

Sq. Ft.

Horsepower.

Diameter, or Side, of Chimney in Inches.

20 ft. High.

40 ft. High.

60 ft. High.

80 ft. High.

100 ft. High.

250 500 750 1,000 1,500 2,000 3,000 4,000 5,000 6,000 7,000 8,000

2.5 5.0 7.5 10.0 15.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0

7.5 9.5 11.4 12.8 15.3 17.3 20.5 23.5 26.0 28.5 30.5 32.5

6.8 8.8 10.3 11.5 13.5 15.3 18.3 20.8 23.0 25.0 27.0 28.5

6.3 8.0 9.4 10.5 12.5 14.0 16.5 19.0 21.0 22.8 24.5 26.0

6.0 6.5 8.8 10.0 11.5 13.3 15.8 17.8 19.5 21.3 23.0 24.3

6.0

7.4

8.5

9.5

11.3

12.5

15.0

17.0

18.5

20.3

21.5

23.5