How to Pressure Test Plumbing with Air

Pressure gauge upclose

A good plumbing system in your home or building allows you to wash dishes, do the laundry, and shower effectively. However, if the water pressure is too high, it puts stress on your plumbing system as well as your appliances. And if it is too low, it makes it nearly impossible to create suds for washing dishes, to properly rinse off in the shower, or to even wash your hands.

Testing your plumbing system with air allows you to assess the condition of your plumbing system without water. It is especially useful in cases where there is no water available on the site, the building is unheated, which can cause the pipes to freeze, or when water leaks can cause damage. However, because compressed gas can cause the pipes to explode under extreme pressure, which can cause personal injury, and in some cases even death, it is especially not recommended for plastic piping or for individuals without extensive knowledge and skills in testing plumbing systems with air.

Learn how to pressure test plumbing with air in seven steps.

Step 1: Turn off the Main Shutoff Valve

If you are testing an existing water pipe system, you first need to turn off the main shutoff valve. Afterward, allow the water to drain from the pipes. Once the all of the water has been drained, shut off the faucets.

For a new system, place a cap on all the stub-outs connected to the system you are assessing. For water systems, solder or glue the caps to test the pipes in your system.
As for drain vent waste systems, you can simply glue a cap to all the stub-outs with plastic pipe cement. Once the testing is complete, cut the caps off.

Step 2: Install the Proper Fittings

For new systems, you may need to install the proper fittings to connect the pressure gauge and the air compressor hose to the system.

As for water systems, this can be done simply by leaving the cap off of one of the stub-outs. Afterward, install a tee and an adapter for the compressor hose and the pressure gauge on that stub-out. For waste systems, you can simply attach an adapter to a clean-out fitting and then install a tee.

Step 3: Connect the Water Gauge

For existing systems, attach the water gauge to either the laundry room faucet or an outdoor faucet that has a threaded spout.

Step 4: Connect the Compressor Hose

Attach an adapter to a different faucet that allows you to connect the compressor hose. Next, attach the compressor to the faucet.

Step 5: Charge the System

Turn on the compressor and allow the pipes to fill with air until the gauge reaches the desired test pressure reading. This test pressure reading is different for water systems and drain systems, so be sure to check the plumbing codes for the proper test pressure reading for your system.

Step 6: Turn off the Compressor

Shut off the compressor and allow the system to pressurize for 15 minutes. At this point, you may remove the compressor hose and leave the pressure gauge in place. It is not uncommon to hear air escaping the pipes if there are leaks present in the system.

If after some time the pressure gauge reading remains the same, then there are no leaks present in the system. However, if the gauge goes down, it indicates a leak in the system.

Step 7: Repairing Plumbing Leaks

If after trying the seven steps how to pressure test plumbing with air, it reveals leaks in your plumbing system, you can simply contact a professional plumber and have the system inspected and repaired. Alternatively, if you feel confident, you can try to repair the leaks yourself.

Most commonly leaks in a plumbing system occur in the joints, meaning any connections between pipes. There are basically three types of joints: IPS joints, compression joints, and soldered joints.

Repairing IPS Joints

Brass IPS joints, which are found in the water system, as long as they are not deteriorated, banged up, or destroyed, can usually be sealed by wrapping Teflon tape around the end of the threads of the pipe three times in a clockwise motion. Next, apply a thin layer of pipe thread sealant around the first three threads. Afterward, attach the pipe to the fitting using your hand and then a wrench until it fits just snug.

Repairing Compression Joints

Compression joints work on a nut and ferrule system that, once the nut and the ferrule are attached, crush down on the pipe creating one pipe. Therefore, if it needs to be repaired, you’ll need to remove the damaged piece and then cut in another pipe to repair it.

Repairing Soldered Joint

A leak in a soldered joint, which often indicates aged corrosion or a poorly soldered joint, can be repaired simply by removing the damaged area. Next, install a new pipe and solder the joints together.

If you notice water leaking from your plastic pipes, and it is coming from the middle of the run, use a pipe cutter or a hacksaw to remove the damaged section of pipe. Afterward, place a plastic compression coupling in its place. Tighten the coupling to seal the pipe. However, remember it is not recommended that you use these steps on how to pressure test plumbing with air to discover leaks in plastic piping. Instead, consider using the water test, which is much safer for plastic.

There are also temporary fixes, such as a pipe clamp or epoxy putty, depending on your pipe material, that you can use to seal your pipes until you can get them repaired. However, don’t put off permanent repairs because water leaks can cause material as well as structural damage. It can also eventually cause the pipes to burst.

You can also check out this view on how to pressure test plumbing with air:

Bottom Line

In the end, how to pressure test plumbing with air takes just 7 steps; however, it is up to the plumber if he or she wishes to assume the risks. If you have implemented these steps and have experienced success, feel free to share your input.


  1. Our daughter has written a contract on a 94-year old 2-story house. 3 Bedrooms/3 Bathrooms. The house was a rehab. The home inspector found that the distribution lines to the water supply are 1/2″, which is undersized to todays standards. Is this a big deal to buy a home with this condition? Her realestate agent is telling her if she asks for this to be corrected before the sale is final, the seller will walk. If this is a big deal, she will just walk from the home. Anything you can offer is greatly appreciated! The house is approximately 2,000 SF. Thanks!

    1. 1/2″ supply lines are not undersized. You should have a 1″ or 3/4″ main for that size home. 3/4″ main lines and then they would reduce in size to 1/2″. If the entire house is 1/2″ that could be a problem. You really increase the velocity of the water which could reduce longevity of the piping.

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