Combustible Gas Detectors for Home Inspectors

by Scotty Bane, InterNACHI® Certified Professional Inspector®


Inspectors should utilize the tools of the trade necessary to perform a full inspection and provide a clear and detailed report. One tool that provides useful information and therefore more value for the home inspection is a combustible gas detector.  Gas leaks are unsafe, as they pose a fire hazard, and they also harm indoor air quality. This tool enables inspectors to track down the source of a gas leak, and helps them identify the components that are emitting gas, as well as the level of concentration.

The combustible gas detector was first developed as a safety device by Dr. Oliver Johnson in 1926 for the company now known as Chevron. His invention helped reduce gas-related accidents by providing early warning and detection. 

Gas meters measure in a variety of ways and provide data in parts-per-million or as a percentage, so they are very sensitive. Natural gas is a common household fuel. At levels from 4.99% or less, or at 15% or greater, the gas is not flammable but should be reported. A quality gas detector can sense gas emissions as low as 0.01%.  

Typical places that a gas detector can be utilized are near stove pipes and burners, and any appliance with a gas ignition. The gas detector needs to be placed within 3 inches of the source. All circulation or vent fans should be turned off while conducting the inspection. Once activated, the gas detector starts reading the air and will give results within about 30 seconds. The inspector can move the detector slowly over the pipes and appliance, and if gas is present, the readings will continue. 

If a gas leak is detected on the property, all parties involved should be notified. If the home has a gas furnace, water heater, or fireplace, all the pipes and connections should be checked for leaks. 

Photos of the meter to show both the location and the readings can be easily included in the inspection report. 

Detectors read combustible gas using infrared, ultrasonic, electrochemical or semiconductor sensors. Infrared sensors provide data through thermal readings. Ultrasonic sensors provide data measuring the distance to a target. Electrochemical sensors detect oxygen and toxic gases, and will lose their sensitivity over time and should be replaced, typically every three years. Semiconductor sensors measure temperature variations. Most detectors, once turned on, will flash or light up, as well as sound a beeping alarm to indicate that gas has been sensed. 

Besides being flammable, combustible gas is also toxic. Some combustible gas detectors also can sense non-flammable toxic gases. An example of a non-combustible but toxic gas is carbon monoxide, which is a byproduct of burned fuels and which is found near stoves, hot water heaters, furnaces, and fireplaces. 

Inspectors should learn all the signs of a gas leak, and not just rely on their gas detector to do the work. An easy way to tell if escaped gas is present in a home is if there are sooty or brownish-yellow stains around a combustible gas appliance. Most gases used in homes, including natural gas and propane, are formulated to have odor, so they are more easily detected. 

The Number One source of carbon monoxide emissions is automobiles. Other sources of toxic gas include fumes from painting, fumigation, construction work, and trash. Some toxic fumes may occur from product off-gassing. Off-gassing is the chemical release of curing paint, stain finishes, and plastics. Off-gassing is also known as the release of very small particles into the air called volatile organic compounds or VOCs. VOCs can cause a variety of health issues, such as eye, nose and throat irritation, nausea, skin problems, headaches, shortness of breath, and fatigue. If the concentration of VOCs is high enough and the exposure time is significant, the lungs, liver, kidneys and central nervous system can be adversely affected. 

Gas detectors typically cost between $40 to $250. Professional-quality tools generally start at around $60, and are available online and at many hardware stores. It’s a good idea to inventory your tools, including your meters, by writing down the brand, model and serial number for your insurance company in order to protect yourself from theft or damage. If the meter’s protective case gets cracked or broken, the tool should be replaced, as the unit itself may be compromised. Typical moisture meters run on AA or AAA batteries. The device maintains its accuracy even if the batteries are low and will simply not function when the batteries do not hold sufficient power. Gas meters can use alkaline, lithium, or rechargeable batteries. It is also recommended by most manufacturers that the batteries be taken out of the tool when not in use in order to prevent corrosion. 

These tools require periodic calibration, which is determined by the manufacturer. As a good professional practice, records should be kept of when the meters are inspected, maintained, and calibrated. 

Every inspector should consider learning how to use a combustible gas detector to enhance the quality of their inspection and report. 

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