Furnace Smells Like Gas? What to Do Right Now
Ben Amina
Aire One East Heating & Cooling, 1910 Dundas St E #117, Whitby
If your furnace smells like gas, treat it as an emergency and leave the house now. Natural gas has no smell of its own, so gas utilities add a chemical called mercaptan that smells like rotten eggs or sulphur. That smell is there for one reason: to warn you about a leak. A gas leak near a furnace can come from a loose fitting, a failing gas valve, a corroded connector, or a problem lighting the burners, and any spark from a light switch, phone, or appliance can ignite it. This guide gives you the exact safety steps to follow first, then explains what can cause a gas smell around a furnace, how to tell it apart from other smells, and what happens once the utility and a licensed technician arrive in Durham Region.
- Get everyone, including pets, out of the house right away.
- Leave doors and windows open behind you if you can do it without delay.
- Do not use phones, light switches, appliances, or electronics inside, and do not smoke or light anything.
- Do not start a car in an attached garage or nearby.
- Once you are safely away, call the Enbridge Gas 24/7 emergency line at 1-866-763-5427 or 911.
- Do not go back inside until the utility or emergency responders say it is safe.
- If your furnace smells like gas, like rotten eggs or sulphur, treat it as a leak until proven otherwise.
- Leave first, then call Enbridge Gas or 911 from outside. Never search for the leak yourself.
- Common causes include loose fittings, a failing gas valve, an old flexible connector, and delayed or failed ignition.
- Some smells that seem like gas come from other sources, but only a gas check can rule a leak out.
- After the utility makes the area safe, a TSSA-certified gas technician must find and repair the cause.
Short answer: if your furnace smells like gas, leave the house immediately without touching switches or phones, and call Enbridge Gas at 1-866-763-5427 or 911 once you are outside. Do not try to find or fix the leak.
After the utility clears the area, a licensed technician repairs the cause. Aire One East offers 24/7 furnace repair across Durham Region. Call 905-576-7600.
Why a furnace smells like gas
A gas furnace is connected to your home’s gas line by a pipe, a manual shutoff valve, and usually a short connector that leads to the furnace’s gas valve. From there, the gas valve feeds the burners, where the gas should light within a second or two of flowing. When a furnace smells like gas, it means gas is escaping somewhere along that path, or it is flowing without lighting right away. Because the smell is added on purpose, even a small amount is noticeable, often well before it reaches a dangerous level. That is exactly why the smell must never be ignored. A furnace that smells like gas may have a tiny leak at a fitting or a serious failure, and only a proper gas test can tell the difference.
6 reasons a furnace smells like gas
- A loose or damaged fitting: threaded joints and unions on the gas pipe can loosen with vibration or age.
- An old flexible gas connector: older connectors can crack or corrode over time.
- A failing gas valve: a valve that leaks internally or at its seals can release gas into the cabinet. Our furnace won’t turn off guide covers a gas valve that will not close.
- Delayed or failed ignition: if the gas flows but does not light right away, a small amount can escape before the furnace shuts it off. A weak furnace igniter or dirty flame sensor can play a part.
- A pilot light that went out: on older furnaces with a standing pilot, a pilot that is out can sometimes let gas escape if the safety does not close fully.
- A leak elsewhere on the gas line: the smell may be near the furnace but coming from the water heater, dryer, range, or another appliance.
Whenever a furnace smells like gas for any of these reasons, it needs a licensed gas technician. In Ontario, work on gas piping, valves, and appliances must be done by a TSSA-certified gas technician.
Smells that are not gas
Some smells near a furnace can be mistaken for gas. They are worth knowing, but the safe rule stays the same: if you think your furnace smells like gas, leave and call first, and let the utility rule a leak out.
| Smell | Common source | What to do |
|---|---|---|
| Rotten eggs or sulphur | Natural gas with added mercaptan | Leave and call Enbridge or 911 from outside |
| Burning dust on first start | Dust burning off the heat exchanger after summer | Usually fades in an hour. See our furnace smells like burning guide |
| Hot plastic or electrical | An overheating motor or wiring | Turn the furnace off and call for service |
| Sewage or drain smell | A dry floor drain or plumbing trap near the furnace | Pour water in the drain, but call the gas line if unsure |
| Rotten eggs from hot water only | A reaction in the water heater tank | Call a plumber or water heater technician |
What not to do when a furnace smells like gas
When a furnace smells like gas, these common reactions can make things worse.
- Do not turn lights or appliances on or off, including the furnace or thermostat.
- Do not use a phone, doorbell, or garage door opener inside the house.
- Do not light a match, lighter, or candle, and do not smoke.
- Do not start a vehicle in an attached garage or near the house.
- Do not look for the leak, sniff around fittings, or try to tighten anything.
- Do not stay inside to grab belongings or close windows.
- If gas is burning, do not try to put it out. Get away and call 911.
What happens after you report that your furnace smells like gas?
When a furnace smells like gas, Enbridge Gas or emergency responders come first. Their job is to make the area safe. They check the air for gas, find the general source, and shut off the gas to the leaking appliance or the whole house if needed. If an appliance is unsafe, it may be tagged so it cannot be used until it is repaired. Our cracked heat exchanger guide explains how red tags work in Ontario.
Next, a licensed gas technician finds out why the furnace smells like gas and repairs the exact cause. They test the gas piping, connector, and valve, tighten or replace fittings, check the gas pressure, and confirm the igniter, flame sensor, and burners light cleanly. Then they leak test the repair, restore gas to the furnace, relight any pilots, and run the furnace through several heating cycles. Our team handles furnace repairs, emergency furnace repair in Ajax, and furnace repair in Oshawa across Durham Region 24/7.
How to prevent gas leaks around your furnace
To lower the chance your furnace smells like gas, book a yearly furnace tune-up, where a technician leak tests the gas connections, checks the gas valve and pressure, and confirms the burners light quickly and cleanly. Ask about replacing an old flexible connector when the furnace is serviced. Keep the area around the furnace clear of storage so a technician can reach the gas line and valve. Install carbon monoxide alarms on every storey and next to each sleeping area, as Ontario now requires, and test them monthly. Our furnace maintenance guide lists everything a visit covers, and our maintenance and protection plans include it every year.
Key terms in this article
- Mercaptan: the chemical added to natural gas so leaks smell like rotten eggs.
- Gas valve: the valve on the furnace that opens to feed gas to the burners.
- Manual shutoff valve: the valve on the gas line beside the furnace that stops gas to the appliance.
- Flexible connector: a short, bendable gas line between the pipe and the appliance.
- Delayed ignition: gas lighting late after building up, often with a bang.
- Leak test: a check of gas joints with a detector or solution after work is done.
Frequently asked questions
| Your furnace gas smell questions, answered |
|---|
| What should I do if my furnace smells like gas? If your furnace smells like gas, get everyone out of the house right away, leaving doors open if you can do so without delay. Do not use phones, switches, or electronics inside. Once you are safely away, call Enbridge Gas at 1-866-763-5427 or 911, and do not go back in until they say it is safe. |
| Is it normal for a furnace to smell like gas? No. A rotten egg or sulphur smell near a gas furnace should be treated as a leak until the gas utility or a licensed technician rules it out. A brief burning dust smell when the furnace first starts in the fall is common, but that is a different smell. |
| Can I turn off the furnace if I smell gas? No. Do not touch the thermostat, furnace switch, or any electrical device, because a spark can ignite gas. Leave the house and let the gas utility or emergency responders shut off the gas. |
| What causes a furnace to smell like gas? Common causes are a loose or damaged gas fitting, an old flexible gas connector, a failing gas valve, delayed or failed ignition, a pilot light that went out on older furnaces, or a leak at another gas appliance nearby. |
| Who fixes a gas leak at my furnace? Enbridge Gas or emergency responders make the area safe first. Then a TSSA-certified gas technician finds and repairs the leak, tests the repair, and restores the furnace. In Ontario, gas work must be done by a licensed gas technician. |
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References and further reading
