Reference Tools & Sample Calculations; For Less Than 8” Wc Initial Supply Pressure; Instructions; Sample Calculation - Noritz NR501-OD Service Manual

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.
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.
Table 1. For Less than 8" WC initial supply pressure
Maximum Natural Gas Delivery Capacity (0.5" Pressure Drop)
Pipe
10' 20'
Size
(3m) (6m)
3/4" 360
1" 678
1 1/4" 1,390
1 1/2" 2,090 1,430
2" 4,020 2,760
2 1/2" 6,400 4,400
3" 11,300 7,780
4" 23,100 15,900
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.
Sample Gas Line
Noritz Condensing Tankless Gas Water Heater
(120,000 Btuh)
Outlet E
10' (3m)
Section 4
Section 3 Section 2
5' (1.5m) 5' (1.5m)
Outlet D
10' (3m)
Gas Fireplace
(25,000 Btuh)
Natural Gas
Meter
30' 40'
(9m) (12m)
247 199 170
466 374 320
957 768 657
1,150 985
2,220 1,900
4,400 3,020
7,780 5,350
12,700 10,900
Barbecue
(50,000 Btuh)
Outlet A
Clothes Dryer
(35,000 Btuh)
Outlet C
5' (1.5m)
Section 1
5' (1.5m)
10' (3m)
5' (1.5m)
Outlet B
Gas Range Stove
(65,000 Btuh)
CAUTION
Length (including fittings)
50' 60' 70'
(15m) (18m) (21m)
151 137 126
284 257 237
583 528 486
873 791 728
1,680 1,520 1,400
2,680 2,430 2,230
4,740 4,290 3,950
9,660 8,760 8,050

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 Calculation - (Using 0.5" WC Pressure Drop Table)
10' (3m)
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"
5' (1.5m)
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"
65
80' 90' 100'
(24m) (27m) (30m)
117 110 104
220 207 195
452 424 400
677 635 600
1,300 1,220 1,160
2,080 1,950 1,840
3,760 3,450 3,260
7,490 7,030 6,640
125'
(38m)
92
173
355
532
1,020
1,630
2,890
5,890