Operating a Combustible Gas Detector to Check for Natural Gas / Propane Leaks During a Home Inspection



Natural gas is piped to probably only 50% or fewer of the homes in the San Antonio, Texas area, but I will commonly hear of concerns about gas leaks from home buyers if there is a gas distribution system present, especially in older homes. When people say a house has “gas”, they’re talking about natural gas, unless you’re in a rural area and have a seperate propane gas tank installed on the property. Although gas is naturally odor-less and taste-less, the gas company adds a sulfur-compound called mercaptan to give gas it’s characteristic “rotten eggs” smell. This mercaptan scent is extremely potent; you can smell the sulfury-smell at just a few parts per million when its in the air.

According to the Texas Real Estate Commision’s Standards of Practice, a home inspector is required to report any gas leaks observed as a deficincy, understandably. This would seem like common sense to many, but it should be noted that the same standards of practice do not require a home inspector in Texas to use any “special tools”, including gas leak detectors.

In practice, this means that if the home inspector smells gas when inspecting a home, he or she will report it as a deficiency and hopefully contact the homeseller or listing agent to let them know of the condition so that they can correct it as soon as possible, for safety reasons. I normally don’t discuss my findings on a home during a buyer’s home inspection with the home seller or the listing agent, but if a matter of safety is present, I will break that rule to prevent injury.


Inspecting for Gas Leaks with a Combustible Gas Detector

We mentioned that natural gas and propane are very smelly because of the mercaptan sulfur substance added to them. How smelly? Well, professionals that work in the gas industry have actually informed me that the human nose can pickup concentrations of gas better than most electronic detectors can, but an individual becomes accostomed to the smell when working in the industry and can no longer pick up on the gas when present. Basically, you get used to it. So they invented combustible gas detectors to help assist in finding gas leaks.

During the course of a home inspection, I use a combustible gas detector to check the accessible gas piping and gas appliance connectors for potential leaks. This typically takes place at the end of the interior home inspection. The device works by first turning it on, and then standing outside, away from any gas exhaust pipes or gas equipment, so that the machine can calibrate itself using the hopefully gas-free outside air as a reference. After about 30 seconds, the combustible gas detector is ready to go. From this point, I retrace my steps throughout the home, stopping at any gas appliance or visible gas piping and place the end of the detector near the joints or connectors of the piping / equipment. My particular device, the TIF-8800, emits a constant noise or beeping sound that gets considerably louder and more obnoxious when it begins to detect any gas. This sound starts of as a gentle “ticking” sound and turns into a full blown whine when natural gas is found.

Where do you place the Combustible Gas Detector?

Some common areas and components I check for gas leaks include:

– A gas water heater and adjacent gas supply piping, especially the gas appliance connector (flexible, corrugated piping leading to the water heater)

– A gas furnace / heating system and adjacent gas supply piping, especially the gas appliance connector again (most comon gas leak point)

– A gas oven, cooktop or range (you guessed it, the gas appliance connector is the common leak area)

– The gas operated fireplace. I will first check the valve area for leaks if the valve is accessible. If it isn’t (a code violation), I will stick the detector inside the area where the key is inserted. I will then check the gas bar for leaks as well. Older gas valves used to be lubricated with a grease that had a tendancy to dry out over time, and are not-uncommon leak points.

– Reasonably accessible gas supply piping, excluding attics and crawlspaces. This is uncommon, as most of the gas supply piping is found in the attic or the crawlspace, but if I see it and it is easily accessible, I will test it. I’ve never found any hard-pipe, such as black-iron gas supply piping that leaks. Probably because the plumber pressure-tested the lines, unlike the guy installing the gas appliance connector.

– Gas valves found on the exterior of the home, such as those for a gas grill.

– Gas valves found on the interior of older homes, such as those that were previously used for individual gas fired heaters. These heaters are no longer suitable for use as they emit carbon monoxide, but the valves are often left in place. We inspect the valves and then recommend that they be capped-off for safety reasons.

– Unvented gas heaters found in bathrooms. Like the gas valves found on the interior of older houses noted above, sometimes these older houses will have a small gas-fired bathroom heater installed. This heater is never tested and should not be operated because they are unvented and emit carbon monoxide, but we will use the combustible gas detector to check for gas leaks around the heater.

– The gas meter itself.

Where do gas leaks most commonly occur?

By a wide, wide margin, most gas leaks occur at the flexible gas appliance connectors. Gas appliance connectors are the ribbed, flexible connectors, commonly about 2-3 feet long but sometimes longer or shorter that are used to connect a gas-burning appliance to the home’s gas supply. The gas appliance connector uses compression to seal the connection, unlike other forms of gas piping which uses a combination of pipe threads and a sealant, often a paste but sometimes a “teflon” tape product. Compression fittings use a bulbous, flared end that is pressed onto a cone-shaped male fitting, and then the metal female end is compressed into the male end via a locking nut that is tightened in place. No sealant is used at this fittings per manufacturer’s recommendations, so if there is any defect in the piping or the installation is performed incorrectly, a leak is possible. Natural gas being piped into your home is not under a lot of pressure, but it doesn’t take much for the gas to slowly leak into an area and begin to collect in an enclosed area.



16400 Henderson Pass, STE 517
San Antonio, TX 78232

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Home Inspector Kyle D. Scott

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