23
Table 5. Capacity of Black Iron Gas Pipe (cu. ft. per hour)
for Natural Gas (specific gravity = .60)
The cubic feet per hour listed in the table above must be greater than the cubic feet per hour of gas flow required
by the furnace. To determine the cubic feet per hour of gas flow required by the furnace, divide the input rate
of the furnace by the heating value of the gas:
Cubic Feet Per Hour Required
=
Input To Furnace (Btu/hr)
Heating Value of Gas (Btu/Cu. Ft.)
NOMINAL
LENGTH OF PIPE RUN
BLACK IRON
(feet)
PIPE DIAMETER
(in.)
10
20
30
40
50
60
70
80
1/2
130
90
75
65
55
50
45
40
3/4
280
190
150
130
115
105
95
90
1
520
350
285
245
215
195
180
170
1 1/4
1050
730
590
500
440
400
370
350
1 1/2
1600 1100
890
760
670
610
560
530
CAPACITY OF BLACK IRON GAS PIPE (CU. FT. PER HOUR)
FOR NATURAL GAS (SPECIFIC GRAVITY - 0.60)
Table 7. Manifold Pressure (in WC) for LP/Propane Gas at Various Altitudes
For a LP Gas Sea Level Heating Value of 2,500 Btu/hr.
Elevation (feet above sea level)
zero to
1999
2000 to
4999
5000 to
5999
6000 to
7999
8000 to
10000
Manifold Pressure Setting (in WC)
Full Input
10
8.5
10
9
8.5
Low Input
5.5
5.5
6.5
6.5
6.5
Table 6. Manifold Pressure (in WC) for Natural Gas at Various Altitudes
For a Natural Gas Sea Level Heating Value of 800 to 899 Btu/cu.ft.
Elevation (feet above sea level)
zero to
1999
2000 to
4999
5000 to
5999
6000 to
7999
8000 to
10000
Manifold Pressure Setting (in WC)
Full Input
3.5
3.5
3.5
3.5
3.0
Low Input
1.7
1.7
1.7
1.7
1.6
For a Natural Gas Sea Level Heating Value of 900 to 999 Btu/cu.ft.
Elevation (feet above sea level)
zero to
1999
2000 to
4999
5000 to
5999
6000 to
7999
8000 to
10000
Manifold Pressure Setting (in WC)
Full Input
3.5
3.5
3.5
3.2
2.8
Low Input
1.7
1.7
1.7
1.6
1.5
For a Natural Gas Sea Level Heating Value of 1,000 to 1,100 Btu/cu.ft.
Elevation (feet above sea level)
zero to
1999
2000 to
4999
5000 to
5999
6000 to
7999
8000 to
10000
Manifold Pressure Setting (in WC)
Full Input
3.5
3.5
3
2.8
2.5
Low Input
1.7
1.7
1.5
1.4
1.3
