Installation Guide

56 Rinnai Tankless Water Heater Installation and Operation Manual
Table 25: Pressure Drop 3.0 in. wc
Example
Rinnai Model Gas Input:
Additional Appliance Total Gas Input:
Heating Value of Gas:
Cubic Feet Per Hour (CFH):
A + B
Intended use: Initial supply
pressure of 8.0 in. wc
or greater.
Schedule 40 Metallic Pipe
Inlet Pressure: Less than 2 psi
Specific Gravity: 0.60
Information in table
obtained from
NFPA 54, ANSI
Z223.1 - 2021.
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
(CFH) =
C
40 (12) 214 448 844 1,730
199,000+65,000
50 (15) 190 397 748 1,540 (CFH) =
1,000
60 (18) 172 360 678 1,390
70 (21) 158 331 624 1,280
(CFH) =
264
3/hr
80 (24) 147 308 580 1,190
For this example, the pipe diameter
must be at least 1/2 in. pipe size and
20 ft (6 m) in length.
90 (27) 138 289 544 1,120
100 (30) 131 273 514 1,060
Natural Gas
Propane (Undiluted)
Table 26: Pressure Drop 0.5 in. wc
Information in table obtained from Schedule 40
Metallic Pipe NFPA 54, ANSI Z223.1 - 2021.
Inlet Pressure: 11 in wc
Specific Gravity: 1.50
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
70 (21) 101 212 400 821
80 (24) 94 197 372 763
90 (27) 89 185 349 716
100 (30) 84 175 330 677
Answer:
Example
Rinnai Model Gas Input:
Additional Appliance Total Gas Input:
Total gas Input
A
199,000
Btu/hr
For this example, the pipe diameter
must be at least 1/2 in. nominal pipe
size and 10 ft (3 m) in length.
B
65,000
Btu/hr
Total Gas
Input
=
A + B
Total Gas
Input
=
199,000 + 65,000
Answer:
Total Gas
Input
=
264,000
Btu/hr
A
Btu/hr
B Btu/hr
C Btu/ft
3
199,000
65,000
1,000