Pressure testing plumbing is a simple way to determine the condition of new and existing plumbing systems. 

Building inspectors require pressure tests to certify that the plumber installed the systems in new construction and renovations are working properly. 

Homeowners might also test their system to track down leaks or troubleshoot low pressure. And learning how to pressure test plumbing isn’t all that difficult.

These tests ensure that fittings aren’t leaking, pipes aren’t cracked, and valves aren’t compromised by pumping air or water into the system. 

This guide will explain how to pressure test plumbing, the fittings required, and some of the nuances necessary for testing the different types of plumbing systems. 

What Tools Will You Need?

Pressure testing plumbing is a fairly simple task, but it does require some tools and fittings to get the job done. Stock up on the following before starting the test:

Tools and Materials for a Plumbing Pressure Test

  • A pair of pump pliers: Used to grip pipes and fittings for tightening and loosening
  • Air compressor with Schrader valve attachment (standard tire valve)
  • Test Pressure Gauge
  • 2-inch-long ¾-inch pipe nipple 
  • ¾-inch to ½-inch pipe coupling
  • 2-inch-long ½-inch pipe nipple
  • Plumber’s tape or pipe thread sealant
  • ½-inch and ¾-inch caps for copper, or
    • ½-inch and ¾-inch caps for PEX
    • ½-inch and ¾-inch plugs for brass
  • 1 ½-inch, 2-inch, 3-inch, and 4-inch caps for DWV
  • DWV test plug
  • Garden hose

How To Pressure Test Plumbing

You’ll need a lot of gear, but pressure testing plumbing isn’t all that difficult. Let’s start with the water system:

How To Pressure Test Water Supply Plumbing

  1. In a home with existing plumbing, ensure that all water supply valves are closed, including:
    • The supply to the home
    • Kitchen faucets, ice makers, and dishwasher valves
    • Bathroom faucets
    • Toilet supply valves
    • Washing machine supply valves
    • Exterior hose valves
    • Any other water fixture in a home
    • There won’t be any water supplied to the home yet, but shut the supply valve anyway
  2. For rough plumbing, install caps on all supply lines except for the shower faucet. For threaded fittings, be sure to use plumber’s tape or pipe thread sealant. 
  3. Using plumber’s tape or pipe thread sealant on all threads, assemble the pressure gauge, ¾-inch nipple, reducer, and ½-inch nipple.
  4. Thread the gauge assembly into the shower faucet elbow and tighten. Be sure you can see the gauge.
  5. Turn the compressor on first, and then open the shower control valve to pressurize the system to the inspector’s specifications (typically two to three times the city’s pressure, between 80 and 120 PSI)
  6. Leave the system for around an hour (or according to the inspector) to ensure that the pressure stays constant.

How To Pressure Test Waste Drain and Vent Plumbing

Generally speaking, waste drain and vent (DWV) testing is only necessary for new construction or renovations. 

Because these systems usually require pressure testing before tying into the street or existing house drain, you can cap them for testing. 

In years past, inspectors frequently accepted pressurizing the system with air. However, most jurisdictions are moving away from this method because plastic PVC can break or explode under pressure. 

Instead, the following method is more generally accepted:

  1. Find all clean-outs and ensure they’re tight, leaving one for testing access.
  2. Place an expandable test cap in the pipe where the system will tie in with the sewer or existing drainage system (sometimes through a clean-out, according to the inspector’s preference)
  3. Seal drain all pipes with caps or plugs, depending on the circumstances
  4. Insert the test plug into the clean-out that was left loose, and fill the system with the garden hose
    • The inspector will usually consider the system as full when water begins to flow out of the highest vent on the roof
  5. Allow the water to sit in the system and check for leaks

While this isn’t a “pressurized test,” the weight of the system being full does create some pressure. 

In some cases, the building inspector will request that you fill the system from one of the vents rather than a test plug. 

Or, in the case of extreme cold, an inspector may allow capping the system off and pressurizing the system with compressed air. 

When Should a Pressure Test Be Done On Plumbing

Pressure testing plumbing might be a bit of a hassle, but it doesn’t have to occur all that often. In fact, there are really only a few cases when you should pressure test a plumbing system.

New Construction

When a builder is constructing a new home, every bit of the home falls under close scrutiny of building inspectors. 

Plumbing inspectors want to ensure that the plumbing system is free of leaks and major issues, and a pressure test is how they check.

Renovations

Major renovations often require building permits, and those involving kitchens or bathrooms typically require plumbing work. 

The building or plumbing inspector might request a pressure test to ensure that everything is working correctly.

Pressure Drop, Leaks, or Odors

Pressure tests aren’t just for inspections. They can also be helpful when looking for the cause of a pressure drop, leak, or odor. 

While a puddle on the floor or crumbling wet sheetrock are dead giveaways to an issue, brick and plaster homes can hide small leaks. 

If a homeowner suspects a leak due to low pressure, water, or odors, a pressure test can help them locate it.

Conclusion

Pressure tests require some specialized gear, and the process of testing the system might be a little messy, but it’s not a difficult task to tackle. 

It’s helpful to call your local plumbing inspector ahead of time and ask about his testing preferences, as tests can vary from municipality to municipality. 

With the above tips and tricks in mind, you should be able to handle any plumbing pressure test the inspectors throws at you.