Reference Tools & Sample Calculations
The tables and samples below are for reference only. The professional sizing and installing the gas
line should always run the appropriate calculations before all installations.
CAUTION
Which Table to Use
• For NG installations with the initial supply pressure at point of delivery (at the meter, for example) is
less than 8” WC, use the 0.5” WC pressure drop table (Table 1).
• For NG installations with the initial supply pressure at point of delivery is greater than or equal to 8”
WC, use the 3.0” pressure drop table (Table 2).
• For all LP installation use (Table 3)
The inlet pressure must be at least 5” WC for NG or 8” WC for LP for all appliances in the gas system.
If the inlet gas pressure drops below 5” WC for NG or 8” WC for LP, the heater may continue to operate,
but the other appliances in the house may experience flame loss or ignition failure, which can result in
gas leakage into the home. Refer to the NFPA 54 for details.
Please contact Noritz for details. For corrugated stainless steel tubing (CSST) capacity tables, please
consult with the manufacturer.
Pipe
Size
Length (including fittings)
10' 20' 30' 40' 50' 60' 70' 80' 90' 100' 125'
(3m) (6m) (9m) (12m) (15m) (18m) (21m) (24m) (27m) (30m) (38m)
3/4" 360 247 199 170 151 137 126 117 110 104 92
1" 678 466 374 320 284 257 237 220 207 195 173
1 1/4" 1,390 957 768 657 583 528 486 452 424 400 355
1 1/2" 2,090 1,430 1,150 985 873 791 728 677 635 600 532
2" 4,020 2,760 2,220 1,900 1,680 1,520 1,400 1,300 1,220 1,160 1,020
2 1/2" 6,400 4,400 4,400 3,020 2,680 2,430 2,230 2,080 1,950 1,840 1,630
3" 11,300 7,780 7,780 5,350 4,740 4,290 3,950 3,760 3,450 3,260 2,890
4" 23,100 15,900 12,700 10,900 9,660 8,760 8,050 7,490 7,030 6,640 5,890
Table 1. For Less than 8” WC initial supply pressure
Maximum Natural Gas Delivery Capacity (0.5” Pressure Drop)
Values in Table are in Cubic Feet of Gas per Hour (0.60 Specific Gravity, 0.5” Pressure Drop, inlet pressure less than 2psi). Contact your gas
supplier for BTU/Cubic Foot ratings. For simplification of your calculations, 1 Cubic Foot of Gas is approximately equivalent to 1000 BTU.
Instructions
1. Size each outlet branch starting from the furthest
using the Btuh required and the length from the meter.
2. Size each section of the main line using the length to
the furthest outlet and the Btuh required by everything
after that section.
Sample Gas Line
Sample Calculation - (Using 0.5” WC Pressure Drop Table)
Outlet A: 45' (13.5m) (Use 50' (15m)), 50,000 Btuh requires 1/2"
Outlet B: 40' (12m), 65,000 Btuh requires 1/2"
Section 1: 45' (13.5m) (Use 50' (15m)), 115,000 Btuh requires 3/4"
Outlet C: 30' (9m), 35,000 Btuh requires 1/2"
Section 2: 45' (13.5m) (Use 50' (15m)), 150,000 Btuh requires 3/4"
Outlet D: 25' (7.5m) (Use 30' (9m)), 25,000 Btuh requires 1/2"
Section 3: 45' (13.5m) (Use 50' (15m)), 175,000 Btuh requires 1"
Outlet E: 25' (7.5m) (Use 30' (9m)), 120,000 Btuh requires 3/4"
Section 4: 45' (13.5m) (Use 50' (15m)), 295,000 Btuh requires 1 1/4"
Natural Gas
Meter
Noritz Condensing Tankless Gas Water Heater
(120,000 Btuh)
Clothes Dryer
(35,000 Btuh)
Barbecue
(50,000 Btuh)
Gas Range Stove
(65,000 Btuh)
10' (3m)
10' (3m)
10' (3m)
10' (3m)
5' (1.5m)
5' (1.5m)
5' (1.5m)
5' (1.5m)5' (1.5m) 5' (1.5m)
Gas Fireplace
(25,000 Btuh)
Section 3 Section 2
Section 1
Outlet A
Outlet B
Outlet C
Outlet D
Outlet E
Section 4
65
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