How many BTU can a 3/4 inch gas line carry?
A 3/4 inch gas line carries 247 CFH (247,000 BTU per hour) on a 20 foot run and drops to 104 CFH (104,000 BTU per hour) by 100 feet. Capacity falls as the run gets longer, which is why the length of the pipe matters as much as its diameter.
Capacity of 3/4 inch Schedule 40 pipe by run length
Natural gas at 1,000 BTU per cubic foot, so CFH multiplied by 1,000 gives BTU per hour. Round your actual run up to the next row — that is the Longest Length Method, and rounding down is how lines get undersized.
| Longest run | Capacity | Equivalent load |
|---|---|---|
| 10 ft | 360 CFH | 360,000 BTU/hr |
| 20 ft | 247 CFH | 247,000 BTU/hr |
| 30 ft | 199 CFH | 199,000 BTU/hr |
| 40 ft | 170 CFH | 170,000 BTU/hr |
| 50 ft | 151 CFH | 151,000 BTU/hr |
| 60 ft | 137 CFH | 137,000 BTU/hr |
| 70 ft | 126 CFH | 126,000 BTU/hr |
| 80 ft | 117 CFH | 117,000 BTU/hr |
| 90 ft | 110 CFH | 110,000 BTU/hr |
| 100 ft | 104 CFH | 104,000 BTU/hr |
| 125 ft | 92 CFH | 92,000 BTU/hr |
| 150 ft | 83 CFH | 83,000 BTU/hr |
| 175 ft | 77 CFH | 77,000 BTU/hr |
| 200 ft | 71 CFH | 71,000 BTU/hr |
What a 3/4 inch line can actually run
Taking the typical appliance ratings below, a 3/4 inch run can carry furnace, tankless water heater, water heater, gas range, gas dryer, standby generator, fire pit at 20 feet. Stretch the same pipe to 50 feet and it covers furnace, water heater, gas range, gas dryer, standby generator, fire pit. At 100 feet it is down to furnace, water heater, gas range, gas dryer, fire pit.
Those are single appliances on their own run. Two appliances sharing the pipe means adding their ratings together before you look at the table.
Before you cut any pipe
These figures come straight from NFPA 54 Table 402.4(2) for Schedule 40 metallic pipe, natural gas at 0.60 specific gravity, inlet pressure under 2 psi and an allowable pressure drop of 0.5 inches water column. That is the ordinary residential case, and it is the same table the PlumbCalc gas line sizing calculator uses.
Two things change the answer on a real job. First, the code sizes the total connected load on a run, not one appliance in isolation — if a second appliance shares the pipe, add its BTU rating before you size. Second, a 2 psi system, a CSST or copper material, or a longer allowable pressure drop all use different tables entirely. Size to the longest run, size to the full load, and confirm against your local code and the appliance data plate before installing.
Propane instead of natural gas
Propane carries 2,516 BTU per cubic foot against natural gas at 1,000, so the same pipe moves far more energy — a 3/4 inch line at 20 feet is worth roughly 621,452 BTU per hour on propane. PlumbCalc sizes propane conservatively against the natural gas table, which returns an equal or larger pipe than a dedicated LP table would. Verify LP jobs against an LP table and local code.
The governing standard is the National Fuel Gas Code, published as NFPA 54 and adopted in most of the United States — see the National Fuel Gas Code for background on the code itself.
Related sizing references
- Full gas pipe sizing chart, every size and length
- Gas line sizing calculator
- Natural gas pipe sizing explained
- Printable pipe sizing cheat sheet
- Capacity of a 1/2 inch gas line
- Capacity of a 1 inch gas line
Frequently asked questions
How many BTU can a 3/4 inch gas line carry?
A 3/4 inch Schedule 40 steel gas line carries 247,000 BTU per hour at 20 feet, 151,000 BTU at 50 feet and 104,000 BTU at 100 feet, using NFPA 54 Table 402.4(2) for natural gas under 2 psi with a 0.5 inch water column drop.
Why does capacity drop as the pipe gets longer?
Friction. Gas loses pressure as it travels, and the table is built around a fixed allowable drop of 0.5 inches water column. A longer run spends that allowance sooner, so the same diameter delivers less. That is why sizing is always done against the longest run in the system, not the average.
Do I size to the longest run or to each branch?
The Longest Length Method sizes every part of the system against the single longest run from the meter to the furthest appliance. It is conservative by design and it is the method most residential installers use. Branch-and-trunk methods can yield smaller pipe but require sizing each segment against its own load and length.
Does this table apply to CSST or copper?
No. NFPA 54 Table 402.4(2) is Schedule 40 metallic pipe. CSST, copper tubing and polyethylene each have their own capacity tables, and CSST in particular varies by manufacturer. Use the table that matches the material you are actually installing.
What if my run is longer than 200 feet?
The table stops at 200 feet. Past that you are into engineered sizing, a larger allowable pressure drop, or a 2 psi system with a regulator at the appliance. Do not extrapolate the table past its last column.