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Why My Propane Furnace Smells Like Sulfur

Eoghan McCloskey

Because propane is combustible, it is indispensable as an ignition source in combustion appliances, such as gas stoves and ovens, water heaters and forced air furnaces. But its combustibility also makes propane potentially dangerous under certain circumstances.

It is important, for the protection of your family and your home, to be able to detect the warning signs that there may be a propane problem in your furnace or any other appliance in your home.

Natural Gas Odors

In its natural state, propane actually does not have any detectable odor. But to aid homeowners in the detection of a gas leak, propane providers add "odorants" to the gas before it reaches your home. The most common odorant used by propane providers is mercaptan, a chemical that gives propane a distinct, sulfur-like rotten egg smell. The use of odorants in propane and other combustion gases is required by federal and state law, so if you smell sulfur near your propane furnace, the chances are good that your propane provider has simply added mercaptan to the propane.

Potential Problems

Simply because the source of the sulfur odor is most likely the propane itself does not necessarily mean that there is a problem with your furnace. If the odor is peculiarly strong, there could be a gas leak near the furnace. Briefly inspect the area around the furnace to see if the sulfur smell is stronger anywhere else; sulfur has such a strong odor that it is possible the gas could be emanating from somewhere near the furnace rather than from the furnace itself.

What to Do

If the sulfur odor is indeed stronger than it should be near the furnace, and if your suspect a propane leak as the cause of the odor, move your family and pets out of the home right away. Do not turn on any electrical switches or light switches and never use a lighter, match or candle as a light source. Call 911 and contact your propane provider from outside of the home. Follow their instructions on what to do and stay outside of the home until authorities declare it safe to re-enter.

Other Possibilities

If the furnace itself is not leaking propane gas, there are several other potential sources of a sulfur odor near your furnace. Sewer gas, a mixture of hydrogen sulfide and other gases, could be seeping into the home through plumbing fixtures or basement floor drains if the sewage system is backed up. Your home's water supply could also be contaminated with high levels of sulfur or with sulfur bacteria. If your suspect the former possibility, a plumber should inspect your plumbing system to see if sewer gas is making its way into the home. In the latter case, report the potential contamination to the city water authority if you use a city water system. If you use a water well, you will likely need to treat the well water using shock chlorination or another chemical treatment method to remove the sulfur and render the water safe to use.