Natural gas is odorless on its own — utilities add a sulphur compound (mercaptan) so leaks are detectable. If you smell rotten egg or strong sulphur in your home, treat it as a real leak until proven otherwise, regardless of how subtle it seems. This page is short on purpose: in a real gas event, you don't need a detailed troubleshooting guide. You need to know the protocol.
Most common causes
The likely culprits, roughly in order of how often we see each one:
- Loose connection at gas appliance
Gas valves, fittings, and unions can loosen over time. Most common at recently-serviced or recently-installed appliances. Gas leak detection equipment finds these in minutes.
- Failed gas appliance valve
Furnace gas valves, water heater gas controls, or stove valves can fail and leak gas. Replacement is straightforward but requires shutting off gas to the appliance during work.
- Cracked or corroded gas line
Older homes occasionally have gas lines with corrosion or cracks. Less common in Halton Hills than in older Toronto neighbourhoods, but possible.
- Pilot light out (some appliances)
On older appliances with standing pilots, a blown-out pilot continues to release gas until safety controls cut off. Modern appliances have shut-off mechanisms but older ones may not.
- External leak in supply line
Rare but serious. Gas supply line from the meter to the home can develop leaks. Usually detected by smell or by visible bubbling in wet ground.
- Sewer gas mistaken for natural gas
Sewer gas (from drain traps that have dried out) can smell similar. Less dangerous than natural gas but still warrants investigation. The smell is usually localized to a specific drain rather than throughout the home.
What to check yourself first
Before calling, walk through these — sometimes the fix is something simple:
- There are no DIY checks for a gas smell
Get out. Call. That's it. Don't try to find the source yourself, don't shut off appliances, don't open windows. Every minute spent investigating is a minute the gas concentration is potentially building.
- Confirm everyone is out
Including pets if you can grab them without delay. Leave doors open as you exit so the house ventilates passively.
- Call from outside, well away from the house
Phones can produce sparks. Get at least 30 feet away before making any calls.
- Note the gas smell strength when you exited
Faint vs strong matters for response. Did the smell increase as you moved through certain rooms? That helps locate the source.
- Don't re-enter to grab anything
No matter what you remembered you needed. Wallet, keys, pets, kids — yes during exit. Anything you forgot, no.
What NOT to do
- Don't flip any switches — light switches included. Spark + gas = explosion
- Don't use phones, garage door openers, or anything battery-powered inside
- Don't open the furnace cover to "look" — even passive ventilation isn't worth the risk
- Don't assume "minor" smell is fine — gas concentration can change rapidly
- Don't re-enter even if the smell seems to dissipate
When to call us
Stop troubleshooting and pick up the phone if:
- Right now, if you currently smell gas
- Faint gas smell that comes and goes (could be intermittent leak — still call)
- Gas smell that's clearly localized to one appliance (still call — even minor leaks matter)
- Gas smell outside near the gas meter (utility issue, also call)
- After any gas appliance install or service if smell appears within hours
Frequently asked questions
What should I do FIRST when I smell gas?
Get everyone out. That's the first action, before anything else. Don't stop to investigate the source, turn off appliances, or even put shoes on if conditions don't require it. Fast exit, then call from a safe distance outside.
Is a faint gas smell really an emergency?
Yes. Faint smells can become strong smells very quickly, depending on the size of the leak and ventilation conditions. Faint also doesn't necessarily mean low concentration — it just means low at your nose location. Other parts of the house may have much higher concentrations.
Who should I call — 911, the gas utility, or you?
In a real gas emergency, any of those three works. 911 dispatches fire department with monitoring equipment. Enbridge's emergency line (1-866-763-5427) sends utility crews directly. We dispatch HVAC technicians who can identify and fix appliance-side leaks. Many homeowners call us first because we're typically faster — but if it's clearly serious (strong smell, multiple rooms, you feel symptoms), 911 is appropriate.
How is sewer gas different from natural gas?
Sewer gas is the gas mixture from drains and sewer lines — typically smells of decomposition or "swampy" rather than the sharp sulphur smell of natural gas. Sewer gas is less explosive and less dangerous than natural gas (still not great, but different category). Localized to a drain or bathroom = probably sewer gas; throughout the home = treat as natural gas until proven otherwise.
Related services
If you need professional repair, the relevant services for this issue: