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Rinnai Tankless Water Heater Installation and Operation Manual 59
Table 25: Pressure Drop 3.0 in. w.c.
Intended use: Initial supply
pressure of 8.0 in. w.c.
or greater.
Information in table
obtained from NFPA 54,
ANSI Z223.1 - 2015.
Nominal Pipe Size (in.)
1/2 3/4 1 1 1/4
Length in ft (meters) Capacity in Cubic Feet of Gas per Hour
10 (3) 454 949 1,790 3,670
20 (6) 312 652 1,230 2,520
30 (9) 250 524 986 2,030
40 (12) 214 448 844 1,730
50 (15) 190 397 748 1,540
60 (18) 172 360 678 1,390
70 (21) 158 331 624 1,280
80 (24) 147 308 580 1,190
90 (27) 138 289 544 1,120
100 (30) 131 273 514 1,060
Natural Gas
Table 26: Example
Rinnai Model Gas Input:
Additional Appliance Total Gas Input:
Heating Value of Gas:
Cubic Feet Per Hour (CFH):
Answer:
For this example, the pipe diameter
must be at least 1/2 in. pipe size and
20 ft (6 m) in length.
A
199,000
Btu/hr
B
65,000
Btu/hr
C
1,000
Btu/ft
3
(CFH) =
A + B
C
(CFH) =
199,000+65,000
1,000
(CFH) =
264
ft
3
/hr
Schedule 40 Metallic Pipe
Inlet Pressure: Less than 2 psi
Specic Gravity: 0.60
Propane (Undiluted)
Table 27: Pressure Drop 0.5 in. w.c.
Information in table obtained from
NFPA 54, ANSI Z223.1 - 2015.
Nominal Pipe Size (in.)
1/2 3/4 1 1 1/4
Length in ft (meters) Capacity in Thousands of Btu per Hour
10 (3) 291 608 1,150 2,350
20 (6) 200 418 787 1,620
30 (9) 160 336 632 1,300
40 (12) 137 287 541 1,110
50 (15) 122 255 480 985
60 (18) 110 231 434 892
80 (24) 101 212 400 821
100 (30) 94 197 372 763
Schedule 40 Metallic Pipe
Inlet Pressure: 11 in w.c.
Specic Gravity: 1.50
Table 28: Example
Rinnai Model Gas Input:
Additional Appliance Total Gas Input:
Total Gas Input:
Answer:
For this example, the pipe diameter
must be at least 1/2 in. nominal pipe
size and 10 ft (3 m) in length.
A
199,000
Btu/hr
B
65,000
Btu/hr
Total Gas
Input
=
264,000
Btu/hr
Total Gas
Input
=
A + B
Total Gas
Input
=
199,000 + 65,000
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