Photograph of an LP gas leak at a flare fitting (C)DJ Friedman 2007 How to find leaks in gas piping: How to Identify & Correct LP Gas or Natural Gas Leaks

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Detect or find gas leaks in natural gas or LP gas / propane piping, fittings, & appliances:

This article describes how to find gas leaks on LP or natural gas piping, regulators, or appliances, and it provides free sample draft home inspection report language for reporting defects in oil and gas piping at residential properties. This article series provides descriptions and photographs of unsafe gas piping, indications of unsafe or improperly operating gas appliances, gas meters, and other gas installation defects are provided.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

How to Test or Look for LP Gas System Leaks

LP gas water heater vent troubles © D Friedman at

Here we outline some common procedures used to test gas piping and fittings for leaks. These procedures should work equally well for both LP gas (propane or bottled gas) systems and for natural gas (piped-in gas from a gas utility company) systems.

Watch out:  improper installation and even improper inspection and testing methods involving natural or "LP" gas can involve dangerous conditions and risk fire or explosion. If you smell gas you should leave the building immediately and should do so without doing anything that could create a spark such as operating a light switch or telephone. From a safe location, call your gas company's emergency line and/or your fire department. The text provided here is a working draft and may be incomplete or inaccurate.

NOTICE: while example report language is provided here, reproduction of this or any of our web pages or their contents at other websites or in printed documents for sale is prohibited.

NOTE: Except that LP gas and natural gas operate at different pressures and thus will have different test pressure specifications. Readers who are interested in gas leak detection equipment should review our article and gas testing warnings at Recommendations for gas measurement instruments & gas detector tubes for indoor gas level tests which includes our description of use of the TIF8800 and similar gas detectors.

Our photo at above left of an LP gas line shutoff shows black staining around the shutoff valve and flare fitting, with some of the black worn away - previously there had been an LP gas leak at this location.

General Safety Warnings for LP or "bottled" or "propane" Gas Installations & Inspections

Immediate LP or natural gas safety hazards: if there is evidence of an LP or natural gas leak at a building, gas odors, for example, you should:

Heating equipment which the inspector (or building occupant or manager) judges to be an immediate life safety hazard should be shut down and appropriate emergency services called.

Pressure testing a gas piping system for evidence of gas leaks

Gas piping repairs, Washington Ave. Brooklyn NY in April 2015 (C) Daniel Friedman These two methods are generally used to test a gas piping distribution system to see if leaks are present.

Our photo above shows Con Edison workers performing gas line replacement & repair work on Washington Avenue in Brooklyn, NY in April 2015. In 2015 the National Transportation Board found that in 2014 a large gas explosion in East Harlem in Brooklyn NY that destroyed two five-story buildings and killed eight people was probably caused by a poorly welded joint in a Con Edison gas line and a break in an old city sewer line. The NTSB previously noted a leaky cast iron gas main that had been installed in 1887.

Thanks to reader Tony Martinez for updating our data on the proper pressure for LP or Natural Gas leak testing. Thanks to another reader JR, an industry manager familiar with gas pressures, who adds that these two fuel gases operate at different pressures. In residential appliances

and adds:

Watch out: Extinguish gas pilot lights - in order to perform pressure-testing methods for LP or natural gas leak detection as discussed above, you will need to extinguish the pilot lights on all gas-fired appliances in the building, and the pilot lights will need to be re-lit again after testing is complete.

Methods used to find and identify points of gas leaks in a gas piping distribution system or at a gas appliance

Some service technicians point to these stains on piping as an evidence of a possible chronic leak in the gas line at this point.

Photograph of an LP gas leak at a flare fitting (C)DJ Friedman 2007 Evidence of an LP gas leak at a flare fitting (C) Daniel Friedman

Indeed on disassembly of a 15-year old LP gas cooktop installed in a New York home I [DF] found this black-stained flare fitting at the connection to the gas inlet nipple of the cooktop. Owners had occasionally smelled a whiff of LP gas but had been unable to find its source, thinking perhaps it was coming from the burners themselves. It wasn't .
See GAS COOKTOP INSTALLATION for photos of the old and new gas appliances involved.

Protracted leakage of fuel gas from a fitting can eventually leave black stains such as shown on the exterior of the flare fitting at above left and the interior of the flare fitting shown at above right.

Gas leak test spray (C) Daniel Friedman

Identifying Sources of Leaks at Brass Flare Fittings on LP Gas Piping Systems

Photograph of a leaky brass flare fitting Photograph of a brass flare fitting in good condition

Here are two brass flare fittings. One of them had a gouge that gave us a gas leak that was a bit tough to find until we disassembled and inspected the leaky joint.

If tightening flared copper tubing connections does not easily correct a leak at that joint, do not just over-tighten the joint (you may break the flare and cause a still larger leak), and do not rely on pipe sealant inside of flared copper tubing fittings.

Open and inspect the flare fitting joint, and replace the flare fittings or make a new copper tubing flared end if necessary.

Also see Advice for Making Flare Fitting Connections with Copper Tubing or Piping where we describe preparation of the flare joint for flexible copper tubing for refrigeration or gas piping lines.

Gas Leak Rates & Volumes

Question: 1mm sq hole ina domestic Gas pipe that went undetected

Anon said:
I had a 1mm sq hole in a domestic Gas pipe that went undetected for 4 years if on average the gas heating was on for 1 hour every day how much gas would i have lost at 1/4PSI


Gas pipe leak calculation:

Assumptions for Gas Leak Rates Through an Orifice:

Using an engineering calculator on gas (air) flow rate, the leak rate would have been

0.0614345 SCFM (standard cubic feet per minute)

Calculating the Total Voluem of Gas Leaked Over an Interval


We calculate the gas leak quantity as follows

0.0614345 SCFM leak rate x 60 minutes per hour = 3.7 cubic feet per hour

3.7 CUFt / Hr / day x 180 days/year x 4 years = 2,664 cubic feet of gas lost to the air

Happily you and your building didn't suffer a fire, explosion or other catastrophe


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