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Pressure Testing Gas Lines for Leaks! Natural Gas and Propane (LP)

Updated: Nov 20, 2023

Fuel gases such as Propane or Natural Gas are a regular part of everyday life for many. Whether it is used to heat a home, cook a meal, or to warm our water, these fuels are constantly around us and as installation and service technicians, it is critical that we be aware of how to safely and accurately pressure test gas lines to test for and prevent potential leaks. In this article, we will be using the IFGC ( International Field Gas Code) 2021 as the reference and discussing the pressure testing of gas lines built for low pressure installations.

Gas lines are commonly installed in buildings that utilize natural gas or propane as the fuel source for central heating systems, water heating, clothes dryers, ovens and ranges, outdoor grills, etc.

Adding a new gas line, pressure testing an existing gas line, and connecting to a supply meter all require city permitting before work begins and approvals during and after work is complete. Make sure to follow all local laws and codes. Make sure to follow instructions and requirements in your locally adopted code book in reference to fuel gas line installation and testing as they supersede anything in this article. Some jurisdictions require licensing before an individual or company can file for a permit to install or pressure test a gas line.

Before Pressure Testing

It is very important that new gas lines be pressure tested prior to being connected to a fuel source and/or any appliances. Pressure testing natural gas (NAT GAS) and propane (LP) is done by adding a typical "15lb or 30lb pressure test gauge" to the empty gas line and adding compressed air through the valve core to increase the pressure to the correct PSIG (pounds per square inch gauge) level. If the pressure drops over a 24hr period, the system has a leak. If it holds, the gas line system does not have a leak. The pressure may fluctuate a little due to temperature changes because air is typically used as the testing medium. Dry mediums such as dry nitrogen can also be used.

Prior to pressure testing, several things must be known and done. The gas lines should be capped off within a few feet of where it will be connected to an appliance (as close as possible). Do Not pressure test a gas line while it is attached to a fuel source. Do Not pressure test a gas line while it is attached to the appliance or you will run the risk of damaging or breaking the built-in gas valve inside each appliance. These electrical gas valves are typically only rated for up to 14"WC which is roughy 1/2 PSI. Also, while it is fine to have ball valves attached to the line being tested, do not rely on ball valves as a means to close off a section of gas line being tested. While a ball valve is designed to stop the flow of fuel gas, they may fail or leak if they are left in the closed position. Keep in mind, most ball valves are only rated to stop about 0.5 PSI. That means even testing a gas line to 6 PSI is well above what that valve is rated to stop internally. Keep the ball valve in the open position while pressure testing and have a cap where the gas line terminates. The pressure test fitting is connected to the other open side of the gas line system.

Now, if you are installing a new section of gas line to an existing manifold or exisitng gas line system, per IFGC ( International Field Gas Code) 2021, you do not have to disconnect all the other appliances and retest the existing gas line. You are only required to pressure test the new section of gas line and afterward, verify that the connection point between the existing and new line does not leak. At least that is what is mentioned in the IFGC 2021. However, technicians must follow the code book and methods that are adopted locally. As a side note, you certainly can test the other exisitng gas lines, especially if you are concerned about their condition or safety. However, appliances must be disconnected first and the lines capped before pressure testing. The outdoor nat gas or LP meter must also be disconnected and capped off. Make sure to apply for proper permitting before disconnecting an existing gas line. New gas line installations always require a permit before work begins.

If you are searching for leaks on an exisitng gas line that is already pressurized with fuel gas, an electronic fuel gas sniffing device can be used and/or anti-corrosive bubble leak detector can be applied to the lines. I have found leaks not only on joints but on the weld seam of a straight gas pipe section so leave no section unlooked!

When Pressure Testing

Typically, when pressure testing low pressure gas lines (below 2PSI), we pressure test to about 6 PSI (usually just over 6 PSI) and there is a reason for that. First, keep in mind that Natural Gas runs at about ¼ PSI while Propane runs at about ½ PSI. We know this because of the following conversions:

· 1 PSI = 27.6” WC (Water Column)

· Natural Gas = 5” to 8” WC = Roughly 1/4 PSI

· Propane = 11” to 13” WC = Roughly 1/2 PSI

When pressure testing gas distribution lines for a low-pressure application, we tend to use a 30 PSI or 15 PSI pressure gauge which is attached to the gas line in a location that can be easily accessed by an inspector (usually outside of the building).

The reason that we pressure test to just over 6 PSI is because the pressure needs to be higher than 1/5th of the gauge range (1/5th of a 30lb pressure gauge is 6 PSI), the gas line must be tested to a level above 3 PSI, and the gas line needs to be pressure tested to at least 1 ½ times the pressure that will be running through the gas line system. (Gas line systems that will run at pressures above 2 PSI have different requirements.) The standards mentioned in this article only refer to low pressure gas line systems that are downstream of the metering regulator. These low pressure gas lines are typically installed in residential and light commercial buildings.

Once the air pressure has been added to the empty lines, monitor the pressure after 5 minutes and tap on the test gauge to see if the needle is hung up and/or falls. If the pressure remains consistant, check again after 1/2 hour, then after 2 hours, and then after the full 24hrs. Note the surrounding outdoor air temperature at these points in time. If the temperature lowers between when you last checked and the most recent check (such as checking the pressure in the afternoon and then the subsequent morning), the pressure may be lower. As the outdoor temperature increases during the day, the pressure will increase. This increase or decrease in pressure may be 1/4 or 1/2 of a PSI. If a drop in pressure is noticed, search for the location of the leak.

The best way to seach is by using a non-corrosive bubble leak detector such as "Big Blu". There are several companies and brands that sell bubble leak detectors. The ones that I find work best come with a dabber and again are non-corrosive or anti-corrosive. Sometimes the location of the leak may be obvious, but other times it will not. In those cases, it is important to attempt to cover as many of the fitting joints with the solution as possible to locate the potential leak(s) in the fewest number of attempts. Be aware, you may need to add additional pressure to the lines in order to detect a leak, especially if most of the pressure has already been lost. Also, do not over-pressurize gas lines as this may cause a leak. Only use specially designed bubble leak detector that is made for this purpose because unlike dish detergent or other corrosive bubbling mixtures, these specially made bubble leak detectors will not cause corrosion or a buildup of rust on the piping. Still, wipe off the sections after leak checking.

On another topic, you may think that the following does not need to be said but I am saying it anyway. Do not use an open flame to check for a potential gas leak on an existing gas line that already has fuel gas in it. Primarily because it is not safe but also because it does not give off an impression of knowledge and safety to the building owner. Additionally, a flame may not ignite the small amount of gas leaking, whereas the non-corrosive bubble leak detectors are specifically designed for leak checking and bubbling very well even with extremely small leaks. Below are a few examples of what a leak may look like on a pipe covered in bubble leak detector.

What to do once you find the leak

Leaks can have several causes and it is important to thoroughly examine the leaking joint once it has been located. The type of connection may also play a big role in the cause of the leak. While it is possible that a fitting is simply loose, there are several other possibilities including a crack in a pipe, bad threads, a poor flare when dealing with copper lines, or even a bad seal due to a poorly cut CSST gas line. Keep these possibilities in mind when attempting to repair any type of gas leak. Make sure the pressure is at 0 PSI before fixing a joint and make sure that the piping is sealed and leak checked before leaving the site.

I hope that this article has helped give you some insight into what it takes to properly pressure test new fuel gas lines! Make sure to follow all local codes and safety requirements, along with the proper code book for your location as they supersede instructions in the article. Also acquire proper licenses and training before working with gas lines.

If you are looking for more information on what was discussed in this article, be sure to check out our Pressure Testing Gas Lines for Leaks! Natural Gas & LP Propane video below!

Published: 5/9/2022 Author: Craig Migliaccio

About the Author: Craig is the owner of AC Service Tech LLC and the Author of the book “Refrigerant Charging and Service Procedures for Air Conditioning”. Craig is a licensed Teacher of HVACR, Sheet Metal, and Building Maintenance in the State of New Jersey of the USA. He is also an HVACR Contracting Business owner of 15 years and holds an NJ HVACR Master License. Craig creates educational HVACR articles and videos which are posted at &

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