A gas line pressure test seals the piping, fills it with air or nitrogen, and watches a gauge to prove nothing leaks. Phoenix follows the International Fuel Gas Code: at least 1.5 times the working pressure, never under 3 psig, held for at least 10 minutes in a single-family home. Any drop means a leak.
What pressure and how long does the code require?
The code sets a floor on both pressure and time, and the plumber can go above either one. Here are the exact rules from Section 406 of the fuel gas code Phoenix enforces.
| Rule | What the code says |
|---|---|
| Test pressure | Not less than 1.5 times the proposed maximum working pressure, and not less than 3 psig |
| Duration, single-family home | Not less than 10 minutes |
| Duration, larger systems | At least half an hour for each 500 cubic feet of pipe volume, never required to exceed 24 hours |
| Test medium | Air, nitrogen, carbon dioxide, or an inert gas. Oxygen is not allowed |
| Gauge | A manometer or a device built to show pressure loss. A mechanical gauge's top reading can be no more than 5 times the test pressure |
| Pass | No evidence of leakage. Any drop on the gauge counts as a leak unless it is clearly from another cause |
Why 3 psig when a house runs far lower? A typical home gas system runs at a fraction of a pound per square inch. A Weber natural gas grill, for example, is designed to run at 7 inches of water column, about a quarter of a psi. Testing well above working pressure gives a real margin, so a joint that barely holds at normal pressure shows up on the gauge.
The gauge rule matters more than it sounds. On a gauge that reads to 100 psi, a small drop at 3 psig barely moves the needle. Keeping the scale to no more than five times the test pressure makes a small leak visible. So the right test is not just the right number. It is the right number on a gauge that can actually show a drop.
You may see other numbers online, often from other codes or other places. In Phoenix, the fuel gas code sets the floor above. The code says "not less than," so a plumber can test higher or longer, and the city inspection is what accepts the work.
How is a gas line pressure test done, step by step?
A pressure test follows a fixed order, and skipping a step can damage equipment or hide a leak. Here is how a licensed plumber runs one.
- 1Clear and expose. The inside of the pipe is cleared of debris, and every joint that is being tested is left exposed so it can be checked.
- 2Protect the appliances. Appliances and valves that are not rated for the test pressure get disconnected and their outlets capped. Manufacturer manuals say the same. Pentair's pool heater manual, for example, says the heater must be disconnected from the piping during any test above half a psi.
- 3Cap and connect the gauge. Open ends get plugged or capped, and the test gauge goes on a fitting on the line.
- 4Pressurize. The line is pumped with air or nitrogen to the test pressure. The source of pressure is then isolated, so the gauge reads only what the pipe itself holds.
- 5Hold and watch. The gauge is watched for the full test time. The city inspection checks the test along with the piping.
- 6Find any leak. If the needle drops, the leak is found with a listed combustible gas detector or a noncorrosive leak detection fluid, like a soap solution. That section gets repaired or replaced, and the test starts over.
- 7Restore gas safely. Once gas goes back in, the code requires a fresh leak check right away, a purge of air from the lines, and a check of every appliance connection before anything is lit.
On a new branch to a new appliance, only the new branch needs the pressure test. The spot where it ties into the old piping gets checked with leak detection fluid instead. The code also lets very small repairs skip a full pressure test when the work is inspected and the connections are checked with an approved leak detection method.
When does a gas line need a pressure test?
A gas line needs a pressure test before it goes into service, before it gets covered up, and after any repair or addition to tested piping. The code's general rule is that every piping installation is visually inspected and pressure tested before it is accepted and first used. It also says piping has to be tested before it is concealed, so a line inside a new wall or under backfill gets tested while it is still exposed.
In Phoenix, the city's gas clearance table ties this to specific situations. A city permit, a city inspection, and a city clearance are required for:
- Any new gas piping, such as a line to a new range, grill, fire pit, or pool heater.
- Any change to existing piping beyond adding an appliance connector.
- A meter locked off by Southwest Gas for a leak on the customer side.
- A repair where gas was shut off at the building.
- An appliance upgrade that adds BTU load and needs pipe sizing, like a bigger water heater or a tankless unit.
Swapping an appliance in kind with no piping changes does not need a city permit. Southwest Gas handles that turn-on. Our guide to whether you need a permit to install a gas line in Arizona covers permits and who can do the work.
What happens if the test fails?
A failed test means the pressure dropped, and the only fix is to find the leak, repair it, and test again. A falling needle is not something to argue with. The code treats any drop on the gauge as a leak unless it can be readily traced to some other cause.
Places a plumber checks when a test fails:
- Threaded joints that were not sealed well or have loosened.
- Old appliance connectors, especially uncoated brass ones, which Southwest Gas warns can separate and leak.
- Valves that leak through the stem or seat.
- Buried steel pipe that has corroded. The code says zinc coating alone is not adequate protection underground, so buried steel without a real coating is a suspect.
- Damage from digging. Customer-owned buried lines are not marked by 811, so shovels and trenchers find them the hard way.
Once the leak is fixed, the whole test runs again from the start. There is no partial credit.
How does the test connect to getting gas turned on?
The pressure test is the proof that lets the gas be turned on or back on. Southwest Gas's Arizona tariff requires the customer to provide "a leak tight system for receiving gas," and the utility runs its own leak check, using natural gas at normal delivery pressure, when it turns service on. If it finds uncontrolled leakage, service is denied until every leak is fixed. The tariff also lets Southwest Gas refuse service until a licensed plumber or a public official certifies the system.
So for permitted work the order is: the plumber installs or repairs and tests, the city inspects the work and the test and issues the gas clearance, and then Southwest Gas turns the gas on and checks for leaks one more time. Only a Southwest Gas employee or agent can turn on the utility's gas at the meter.
If someone asks you for written proof that your system passed, that is a gas leak inspection and certification, which is built around this same test. HQ Plumbing & Air runs pressure tests on residential and commercial natural gas systems as part of our gas leak inspection and gas line work, with the results in writing.
A pressure test is short, but it is the one step in gas work that tells you for certain whether the pipe is tight. That's the whole point of it.