How do I tell the difference between a gas leak and sewer gas?

A gas leak produces a rotten-egg odor that is strongest near the furnace or gas lines. Sewer gas has more of a raw sewage or decay character and tends to be most noticeable near bathroom or floor drain vents. If there's any uncertainty, treat it as a gas leak and get out.

Can a small gas leak go undetected?

It can. Very minor leaks may only produce a noticeable odor when the furnace is actively running. If you catch an occasional whiff of gas that then fades, don't dismiss it — contact your gas company for a formal leak test. Every gas leak, regardless of size, must be repaired.

Who repairs gas leaks on HVAC equipment?

Your gas utility will locate the leak and may shut off gas to the appliance, but they generally don't perform the actual repair. A licensed HVAC contractor is responsible for repairing furnace gas lines and connections.

Rotten Egg Smell from HVAC — Gas Leak Warning

Rotten egg or sulfur odor near your HVAC? This could signal a gas leak — learn the warning signs and the safety steps to take immediately.

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Professional Rotten Egg Smell from HVAC — Gas Leak Warning in Asheville & Western NC

Treat This as an Emergency Until Proven Otherwise

In its natural state, natural gas has no smell. Utility providers mix in mercaptan — a chemical with a distinctive rotten-egg or sulfur odor — specifically so leaks can be detected. Any rotten-egg smell near your furnace, HVAC system, or coming through the vents should be treated as a possible gas leak until it's been ruled out. This is not a wait-and-see situation — it calls for action right now.

Steps to Take Immediately

Do NOT touch light switches, use a phone while still indoors, strike a match, or turn on any electrical device — even a small spark can ignite escaping gas. Open exterior doors and windows on your way out. Get everyone — family members and pets — out of the house without delay. Once safely outside, contact your gas utility's emergency line (Asheville area: PSNC Energy/Dominion Energy at 1-877-776-2427) and call 911. Stay out until the gas company clears your home as safe to re-enter.

Sulfur Smells That Aren't Actually Gas Leaks

Once safety has been confirmed, several non-gas sources can produce rotten-egg or sulfur-like odors from HVAC systems. A dried-out P-trap on the condensate drain may allow sewer gas to seep into the ductwork. A deceased animal decomposing inside a duct produces a sulfurous decay odor. A failing or overheating electrical component occasionally gives off a sulfur-like scent. And homes on well water may have hydrogen sulfide in the supply that enters indoor air through humidifier equipment. These causes are unpleasant but pose no explosion risk the way a gas leak does.

Once the Situation Is Under Control

When the gas company locates a leak, they'll shut off gas to the affected appliance. You'll then need a licensed HVAC contractor to repair the gas connection before service can resume. Quality Mechanical handles gas piping and furnace gas connections across Asheville and WNC. If the smell turns out to be unrelated to gas, we can track down and fix the actual source — whether it's a drain issue, a duct problem, or a failing component.