Most Likely Causes (Ranked)
If your home uses natural gas or propane, a gas smell should be treated as a leak until confirmed otherwise. Natural gas is odorless in its pure form — utilities add mercaptan (a sulfur compound) to give it that distinctive smell. Leaks most commonly occur at appliance connections (stove, furnace smell, water heater, dryer), gas valve fittings, corroded gas lines, or damaged flexible connectors. Even small leaks are dangerous because gas accumulates in enclosed spaces and can reach explosive concentrations (5-15% for natural gas).
If you have a gas stove, a faint gas smell near the stove is the most common and least dangerous cause. An extinguished pilot light (on older stoves), a burner that wasn't fully turned off, or a burner that didn't ignite properly all release small amounts of unburned gas. Modern stoves have safety valves that shut off gas flow if the flame goes out, but older models may not.
Sewer gas contains hydrogen sulfide, which has a sulfur-like smell that many people describe as similar to natural gas. This is the most common "false alarm" for gas leak concerns. sewer gas typically enters through dried-out P-traps (the U-shaped pipes under drains), failed wax rings on toilets, or cracked sewer vent pipes. It's unpleasant and can cause headaches in high concentrations, but it's not explosive like natural gas.
Certain household chemicals, solvents, adhesives, and paint products contain volatile organic compounds (VOCs) that can produce a gas-like or chemical smell. New furniture, fresh paint, refinished floors, or stored chemicals in a garage or utility room can release these compounds. While usually not dangerous at typical residential concentrations, the smell can be mistaken for a gas leak.
How to Fix It
If You Suspect a Gas Leak (Act Immediately)
Free (gas company response)This is the only response if you think you have an actual gas leak. Don't try to find or fix it yourself.
- 1Do not turn on or off any light switches, electrical appliances, or create any spark. Don't use your phone inside the house.
- 2Do not light matches, lighters, or candles. Don't smoke.
- 3Open windows and doors as you walk toward the exit — but don't delay leaving.
- 4Leave the house immediately with all family members and pets.
- 5Call your gas company's emergency line from outside (at least 100 feet away from the house). If you don't know the number, call 911.
- 6Do not re-enter until the gas company clears the house. They have gas detectors that can confirm whether a leak exists and measure its severity.
- 7If a leak is found, the gas company will shut off the supply and mark the leak location. A licensed plumber or gas technician will then need to make the repair before service is restored.
Fix a Stove Burner Issue
$0-150If the smell is clearly from the stove and is faint, this may be a simple fix.
- 1Check that all burner knobs are fully in the off position — sometimes a knob gets bumped to barely-on, releasing gas without igniting.
- 2For stoves with standing pilot lights: locate the pilot (usually under the stovetop, accessible by lifting the top panel) and relight it according to the manufacturer's instructions. If it won't stay lit, the thermocouple may need replacement ($10-30 part, $100-150 with service call).
- 3For stoves with electronic ignition: if a burner clicks but doesn't light, the igniter may be dirty or misaligned. Clean the igniter with a dry toothbrush. If it still doesn't ignite, the igniter may need professional replacement.
- 4If you smell gas from the oven specifically, the oven igniter may be weak — it glows but doesn't get hot enough to open the gas valve, allowing a small amount of gas to accumulate. Oven igniter replacement is a common repair ($100-200 including parts and labor).
Fix Sewer Gas Intrusion
$0-300If the gas smell is near drains rather than gas appliances, sewer gas is the likely culprit.
- 1Run water in every drain in the house for 30-60 seconds, including guest bathrooms, basement floor drains, and any drain that hasn't been used recently. This refills P-traps and blocks sewer gas.
- 2Add a tablespoon of mineral oil to rarely-used drains — it sits on top of the water and slows evaporation, keeping the P-trap sealed longer.
- 3Check the wax ring seal on toilets by looking for water stains at the base. If the toilet rocks when you push it, the wax ring may be compromised. Replacement costs $5-15 for the ring plus about $100-150 labor if you hire a plumber.
- 4Have a plumber check sewer vent pipes (on the roof) if the smell persists. A blocked or cracked vent can cause sewer gas to be pushed back into the house rather than exhausting through the roof.
When to Call a Professional
The gas smell is strong and you feel dizzy, nauseous, or have a headache — leave the house immediately. These are symptoms of gas exposure. Call your gas company and 911 from outside.
You hear a hissing sound near a gas appliance or line — this strongly indicates an active gas leak. Do not investigate further. Leave and call for help.
The gas smell appeared suddenly and is very strong — a sudden onset of a strong gas smell (versus a faint smell that builds gradually) suggests a significant leak that needs immediate attention.
Your carbon monoxide detector is alarming — CO is a byproduct of incomplete gas combustion. A CO alarm combined with a gas smell suggests a malfunctioning gas appliance. Leave immediately and call 911.
You smell gas near the gas meter outside — an outdoor gas smell near the meter or service line is your gas utility's responsibility to investigate and repair.
How to Prevent It
Install natural gas detectors — wall-mounted gas detectors ($30-50 each) will alarm before gas reaches dangerous concentrations. Install one near the floor in the kitchen, near the furnace smell, and near the water heater.
Schedule annual gas appliance inspections — a licensed HVAC technician should check all gas connections, the furnace smell heat exchanger, and the water heater annually. Many gas companies offer free safety inspections.
Replace old flexible gas connectors — older brass connectors (pre-1990) are prone to cracking. Modern stainless steel braided connectors are much safer. A plumber can replace all connectors in the house for $200-400.
Know where your gas shutoff is — the main shutoff valve is at your gas meter (outside). You'll need a wrench to turn it. Practice finding it now, not during an emergency.
Run water monthly in all drains — prevents sewer gas intrusion from dried P-traps, which is the most common non-emergency cause of gas-like smells.
Natural Gas vs. Propane: Key Differences
If your home uses propane (common in rural areas without natural gas service), the response to a suspected leak is largely the same — leave and call your propane supplier. However, there's one critical difference: propane is heavier than air and sinks to the floor, while natural gas is lighter and rises to the ceiling.
This means propane leaks are more dangerous in basements and low-lying areas because the gas pools at floor level and can reach explosive concentrations more quickly. If you smell propane in a basement, the situation is especially urgent. Propane gas detectors should be installed near the floor, while natural gas detectors are effective at any height.
Propane also has a slightly different smell than natural gas — many describe it as more chemical or slightly sweet compared to the sulfurous rotten-egg smell of natural gas. Both are added odorants, not the natural smell of the gas.
What Happens When You Call the Gas Company
Calling your gas company's emergency line is always free, and there is never a charge for a leak investigation — even if it turns out to be a false alarm. Gas companies take every call seriously because the liability of an undetected leak is enormous.
A technician will arrive (typically within 30-60 minutes) with a combustible gas detector that can measure gas levels in parts per million. They'll check around appliances, gas lines, the meter, and any area where you reported the smell. If a leak is found, they'll shut off the gas supply to the affected appliance or, if necessary, the entire house.
You'll then need a licensed plumber or gas fitter to make the repair, which must pass inspection before the gas company restores service. Don't view this as an inconvenience — a confirmed leak is a confirmed hazard that was actively filling your home with explosive gas. The temporary disruption is nothing compared to the alternative.
Frequently Asked Questions
No. Even a faint gas smell should be investigated before sleeping in the house. Natural gas displaces oxygen, and a leak that seems minor during the day can reach dangerous concentrations overnight in a closed house while you sleep. Open windows for ventilation and call your gas company for an inspection. If the gas company clears the house, you can sleep safely. If you can't get an inspection until morning, sleep with windows open and gas appliances turned off.
Yes. At low concentrations (before reaching explosive levels of 5-15% in air), natural gas exposure can cause headaches, dizziness, nausea, fatigue, and breathing difficulties. Prolonged exposure in an enclosed space can lead to unconsciousness. If you experience any of these symptoms and smell gas, leave the house immediately and call 911.
The gas company inspection is always free. Repair costs depend on the source: tightening a loose fitting may cost $50-100 for a service call. Replacing a flexible gas connector is $75-200. Repairing or replacing a section of gas pipe is $150-500. A full gas line replacement (rare, usually only in very old homes) can cost $2,000-5,000+. Never attempt gas line repairs yourself — this is always a job for a licensed professional.
No. Standard carbon monoxide detectors do not detect natural gas or propane. CO detectors sense carbon monoxide, which is produced by incomplete combustion of gas — not by leaking unburned gas. You need a separate combustible gas detector ($30-50) to detect gas leaks. Some combination units detect both CO and gas. If your CO detector IS alarming and you smell gas, it means a gas appliance is both leaking and burning incompletely — leave immediately and call 911.