Heat units emitted per square foot of actual surface per hour, per degree of difference in temperature.

Natural Draft, Extended Surfaces

Height of Flue.

Feet.

Velocity of Air per

Second.

Feet.

*B.T.U. Emitted.

5

2.90

1.70

10

4.10

2.00

15

5.00

2.22

20

5.70

2.38

25

6.30

2.52

Height of Flue.

Feet.

Velocity of Air per

Second.

Feet.

B. T.U Emitted.

30

6.70

2.60

35

7.14

2.67

40

7.50

2.72

45

7.90

2.76

50

8.20

2.80

Draft, Plain Surfaces

Velocity of Air per

Second.

Feet.

* B.T.U. Emitted

3

3.42

4

4.00

5

4.50

6

4.94

7

5.33

Velocity of All per

Second.

Feet

B. T. U.

Emitted.

8

5.71

10

6.33

12

6.93

14

7.50

16

8.06

Velocity of Air per

Second

Feet

B.T.U Emitted.

18

8.50

20

9.00

22

9.42

24

9.79

* A British thermal unit is the quantity of heat necessary to raise the temperature of 1 lb. of water 1° F.