33
Installation (Continued)
Table 3-4
Sizing Natural Gas Pipe Mains & Branches
Sizing Natural Gas Pipe Mains & Branches
Gas Input (Cubic Feet/Hour)* Notes:
1. If more than one unit is served by
Gas Supply 1-1/4" 1-1/2" 2" 2-1/2" 3" 4"
the same main gas supply, consider
Pipe Run (ft) Pipe Pipe Pipe Pipe Pipe Pipe
the total gas input (cubic feet/hr.)
10
1050 1600 3050 4800 8500 17500 and the total length when determining
20
730 1100 2100 3300 5900 12000 the appropriate gas pipe size.
30
590 890 1650 2700 4700 9700 2. Obtain the Specific Gravity and
40
500 760 1450 2300 4100 8300 BTU/Cu.Ft. from the gas company.
50
440 670 1270 2000 3600 7400 3. The following example demonstrates
60
400 610 1150 1850 3250 6800 the considerations necessary when
70
370 560 1050 1700 3000 6200 determining the actual pipe size.
80
350 530 990 1600 2800 5800
90
320 490 930 1500 2600 5400 Example: A 40' pipe run is needed to
100
305 460 870 1400 2500 5100 connect a unit with a 500 MBH furnace to a
125
275 410 780 1250 2200 4500 natural gas supply having a rating of 1,000
150
250 380 710 1130 2000 4100 BTU/Cu.Ft. and a specific gravity of 0.60
175
225 350 650 1050 1850 3800
200
210 320 610 980 1700 3500 Cu.Ft/Hour = Furnace MBH Input
* Table is based on a specific gravity of 0.60. Use Table 3-1 for Gas BTU/Cu.Ft. X Multiplier (Table 3-1)
specific gravity of the local gas supply. Cu.Ft/Hour = 500
Table 3 indicates that a 1-1/4" pipe is required.
Specific Gravity Multipliers
Specific Gas Heating Capacity Altitude Correction Factors
Gravity Multiplier
0.50 1.10
Sea Level 2001 2501 3501 4501 5501 6501
0.55 1.04 To 2000 To 2500 To 3500 To 4500 To 5500 To 6500 To 7500
0.60 1.00
Capacity
0.65 0.96 Multiplier 1.00 .92 .88 .84 .80 .76 .72
Note: Correction factors are per AGA Std. 221.30 - 1964, Part VI, 6.12.
Local codes may supersede.
Altitude (Ft.)
Figure 3-10
Unit Gas Trains (Natural Gas)
235 and 350 MBH
500 and 850 MBH
