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

Gas leaks smell like rotten eggs and are strongest near the furnace or gas lines. Sewer gas is more of a sewage or decay smell and is often strongest near bathroom or floor drain vents. When in doubt, treat it as gas and evacuate.

Can a small gas leak go undetected?

Yes. Very small leaks may only be noticeable when the furnace is running. If you occasionally smell gas but it goes away, do not ignore it — call your gas company to perform a leak test. Any gas leak, no matter how small, needs repair.

Who repairs gas leaks on HVAC equipment?

The gas company will identify the leak and may shut off gas to the appliance, but they typically don't perform repairs. A licensed HVAC contractor handles furnace gas line and connection repairs.

Rotten Egg Smell from HVAC — Gas Leak Warning

A rotten egg or sulfur smell near your HVAC system could indicate a gas leak — know the warning signs and safety steps.

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

This Is a Potential Emergency — Act Immediately

Natural gas is odorless in its natural state. Utility companies add mercaptan — a chemical that smells like rotten eggs or sulfur — so you can detect leaks. If you smell rotten eggs near your furnace, HVAC system, or coming through your vents, treat it as a potential gas leak until proven otherwise. This is not a situation for troubleshooting or waiting — it requires immediate action.

What to Do Right Now

Do NOT flip any light switches, use your phone inside the house, light matches, or operate any electrical equipment — sparks can ignite gas. Open doors and windows as you exit. Leave the house immediately with all family members and pets. Once you're safely outside, call your gas company's emergency line (for Asheville area: PSNC Energy/Dominion Energy at 1-877-776-2427) and call 911. Do not re-enter the home until the gas company has cleared it as safe.

Not Every Sulfur Smell Is a Gas Leak

After safety is confirmed, there are non-gas-leak causes of rotten egg or sulfur smells from HVAC systems. A dried-out P-trap in a condensate drain can allow sewer gas to enter the ductwork. A dead animal in the ductwork produces a sulfurous decay smell. A failing or overheating electrical component can sometimes produce a sulfur-like odor. And if you're on well water, hydrogen sulfide in the water can enter the air through humidifier systems. These are unpleasant but not dangerous in the way a gas leak is.

After the Emergency Is Resolved

If the gas company identifies a leak, they'll shut off gas to the affected appliance. You'll need a licensed HVAC professional to repair the gas connection before service can be restored. Quality Comfort handles gas piping and furnace gas connections throughout Asheville and WNC. If the smell turns out to be a non-gas issue, we can diagnose and fix the source — whether it's a drain issue, ductwork problem, or component failure.