Gas pipe sizing calculator
Add the appliances on the line, enter the length of the longest run, and get the Schedule 40 steel pipe size and a capacity chart for that length.
Inputs
Result
Capacity of Schedule 40 steel pipe at 60 ft, 0.5 in. w.c. drop
Natural gas, specific gravity 0.60. MBH uses the heating value entered above.
| Nominal size | Inside dia., in | Capacity, cfh | Capacity, MBH |
|---|
How to use it
- List the appliances fed by the section you are sizing, with the input rating from each nameplate.
- Measure the longest run: the developed length from the meter or regulator to the farthest appliance on the system.
- Use that same length for every section of the system, and size each section for the appliances downstream of it.
That is the longest-length method in IFGC 402.4.1. It is conservative for the sections near the meter, and it is what the code's sizing tables are built for.
How it works
The code's capacity tables come from a low-pressure flow equation in IFGC 402.4 and NFPA 54. The calculator uses it directly:
It reproduces the published table values, for example 172 cfh for 1/2 in. pipe at 10 ft with a 0.5 in. drop, and 104 cfh for 3/4 in. at 100 ft. Gas flow in cfh is the appliance load in BTU/h divided by the heating value.
Questions
What size gas line does a tankless water heater need?
A 199,000 BTU/h tankless heater on its own needs 3/4 in. Schedule 40 steel up to about 25 ft and 1 in. from about 30 to 60 ft, at a 0.5 in. w.c. pressure drop. Size the whole system, not just the heater's branch, because the trunk carries every appliance.
How do I measure the length?
Measure the developed length of pipe from the meter or second-stage regulator to the farthest appliance, following the pipe rather than a straight line.
Should I use 0.3 or 0.5 in. w.c. pressure drop?
Use the drop your adopted code and utility allow for the supply pressure you have. 0.5 in. w.c. is common for standard low-pressure residential systems; 0.3 gives a more conservative result.
Can I use this for propane?
No. Propane has a different specific gravity and heating value and uses its own tables. This calculator is for natural gas only.
How many BTU is one cubic foot of gas?
About 1,000 BTU for natural gas, though it varies by utility, typically between 1,000 and 1,050 BTU per cubic foot.