What Pressure Test Is Required After Installing or Changing a Gas Line? (IRC 2018)

Quick Answer

IRC 2018 Section G2417.1 requires that all new gas piping be tested before being placed in service. The standard residential test is 3 psi air pressure for a minimum of 15 minutes with no pressure drop. The test must be performed with air or an inert gas — never with the actual natural gas or LP — and must be witnessed by or reported to the inspector. Connections to appliances are typically isolated during the test using listed caps or plugs.

What G2417.1 Actually Requires

IRC 2018 Section G2417.1 establishes piping inspection and test requirements. It requires that before any gas system or part thereof is placed in service, it shall be tested and proved tight under a test pressure of not less than 3 psig (pounds per square inch gauge). The test medium must be air, nitrogen, CO2, or another inert gas — natural gas or LP may not be used as the test medium inside a structure. The 3 psi pressure must be maintained for at least 15 minutes without any perceptible pressure drop, as measured by a gauge with a range that allows reading a 0.5 psi drop clearly.

G2417.1.1 provides an alternative for existing systems when only a portion of the piping has been modified. If the modification is minor — such as replacing a fitting or adding a branch — a test of the new section at 3 psi may be substituted for a full system test, provided the existing portions are not disturbed. However, if any existing joints are opened and remade, those joints must be included in the test section.

The pressure test must be performed before the piping is covered, insulated, or enclosed. An inspector must either witness the test or review a test report signed by the licensed contractor. If the pressure drops during the test, all joints must be checked with a listed gas leak detection solution or electronic detector, the leak must be repaired, and the test must be repeated from the beginning. The test pressure must not exceed the service pressure rating of the lowest-rated component in the system — for CSST in residential systems, the service pressure is typically rated well above 3 psi, but always verify.

After a successful test, the piping is purged of air per G2417.4 before the gas service is restored. Gas appliances are then reconnected and tested for operation at normal service pressure.

IRC 2018 Section G2417.1 requires that gas piping be pressure tested before being put into service. The standard test for systems operating at pressures up to 0.5 psig (standard residential operating pressure) requires a test pressure of at least 3 psig for a minimum duration that allows the inspector to verify each joint. For systems operating above 0.5 psig (systems with medium-pressure gas piping up to 2 psig), the test pressure must be at least 10 psig. The test medium must be air or inert gas. Testing with gas (methane or propane) is prohibited because a leak during testing would release combustible gas into the building. The test must be performed before the system is connected to the gas meter and before any appliances are connected, so that a failed test does not require disconnecting the meter or multiple appliances. A failed pressure test requires identifying and repairing the leak, retesting, and calling the inspector back for a re-inspection before the system can be connected to the supply.

Why This Rule Exists

Gas piping is installed inside walls and enclosed spaces where a small leak, undetected for years, can accumulate to explosive concentrations. A pressure test before service identifies every leaking joint before the system is enclosed and before gas is introduced. Testing with air rather than gas means that if a large leak exists, there is no fuel accumulation. The 3 psi test pressure — substantially above the typical residential operating pressure of about 0.25 psi — stresses the joints enough to reveal pinholes and loose fittings that would not register at operating pressure.

This requirement reflects the fundamental principle of the IRC that electrical and mechanical systems must be installed in a manner that protects occupants over the life of the building, not just at the moment of installation. Proper installation documented at inspection provides future owners and service technicians with confidence that the system was built to code, reducing liability and preventing disputes about pre-existing conditions.

What the Inspector Checks at Rough and Final

At rough inspection (if scheduled before piping is covered), the inspector may witness the pressure test. At final inspection, the inspector will require proof of a successful pressure test — either a witnessed test, a contractor-signed test report, or a test performed at the time of inspection. The inspector will check: the test pressure was at least 3 psi, the test duration was at least 15 minutes, the test medium was air or inert gas (not natural gas), no appliance connections were pressurized above their rated inlet pressure (appliances should be isolated), and any leaks found were repaired and the test was repeated.

What Contractors Need to Know

Use a calibrated test gauge with appropriate resolution — a 0 to 30 psi gauge is appropriate for a 3 psi test. A 0 to 300 psi gauge cannot reliably show a 0.5 psi drop. Cap all appliance stub-outs with listed plugs before pressurizing. Do not test through appliance flexible connectors — cap upstream of the connector. Bleed pressure slowly from the system after a successful test to avoid hammering fittings. Document the test with a written record including the date, pipe section tested, test pressure used, test duration, and result. Provide this documentation to the inspector. Always perform the test before insulating, drywalling, or burying any pipe.

Use a calibrated digital pressure gauge for gas piping pressure tests rather than a dial gauge. Digital gauges provide more precise readings and can detect very small pressure drops that indicate a slow leak. A 3 psig test on a residential gas system that drops 0.1 psig in 15 minutes may indicate a very small leak that is too slow to detect by soap bubble testing but will accumulate over time in an occupied building. Conduct the leak test with the system pressurized, then soap-test all joints systematically. When testing after appliance connections are added to an existing system, isolate the new piping run with a ball valve for testing, then re-test the complete system after confirming the new segment is leak-free. This staged testing approach identifies leaks in the new work before they are masked by acceptable pressure loss in the existing large-volume system.

What Homeowners Get Wrong

Many homeowners believe that simply turning on the gas and checking for odors constitutes a sufficient leak test. It does not. Low-level leaks may not be detectable by odor until gas concentrations are already at dangerous levels. The pressure test detects leaks that an odorant-based check cannot. Another common error is testing through open appliance connections — this sends 3 psi through flexible connectors and appliance regulators that may be rated for only 0.5 psi, potentially damaging them. Always cap appliance connections before testing.

State and Local Amendments

IRC 2018 states — TX, GA, VA, NC, SC, TN, AL, MS, KY, and MO — follow the 3 psi / 15-minute test requirement of G2417.1 without significant modification. Texas requires a test at 10 psi for commercial systems, but the 3 psi residential standard applies to one- and two-family dwellings. Some local gas utilities specify that the pressure test be performed with nitrogen rather than air to avoid moisture introduction. Confirm with your local AHJ and utility whether any additional test requirements apply.

IRC 2021 did not change the 3 psi / 15-minute test requirement. It added clarifying language in G2417.1 about test gauge resolution requirements and reinforced that tests must use air or inert gas, not the distributed gas.

When to Hire a Licensed Gas Contractor

Gas pressure testing requires a licensed contractor in most states because the test involves pressurizing a live system and repairing any failures found. A licensed contractor has the test gauges, knowledge of which joints to isolate, and the leak detection equipment needed to locate and repair failures. The contractor must sign the test documentation, which may be required by both the inspector and the homeowner's insurance company. Never pressurize gas piping with the building's occupants present during the test period.

Common Violations Found at Inspection

• Test performed at less than 3 psi — gauge shows only 1 to 2 psi due to pressure bleed-down during test setup
• Test duration less than 15 minutes — contractor called the inspector before the required hold period was complete
• Test performed with natural gas (flammable) rather than air — creates hazardous condition if a large leak exists
• Appliance connections not isolated during test — flexible connectors or appliance regulators pressurized beyond their ratings
• Test gauge too coarse to read a 0.5 psi drop — 0 to 300 psi gauge used for a 3 psi test
• No written test record available for inspector review
• Existing joints that were opened and remade during a modification not included in the test section
• Piping covered with drywall or insulation before test was performed