Most Likely Causes (Ranked)
High-efficiency furnaces vent through PVC pipe using mechanical joints or solvent-welded connections. PVC joints can crack from settling, and solvent-welded joints fail from improper application. The condensation in the vent is acidic and pools at sags, eventually softening the PVC. Proper slope toward the furnace allows condensation to drain back.
Black iron gas pipes corrode over decades, especially in damp areas. Physical damage from construction or accidents can crack lines.
Gas valves on stoves, heaters, and fireplaces wear internally, allowing small amounts of gas to pass when off.
Flexible corrugated stainless gas connectors have limited lifespan (10-20 years) and can fail from kinking or corrosion.
Tree roots, construction, and ground shifting can damage underground gas lines.
How to Fix It
EMERGENCY: Leave and Call
Free- 1If you smell gas: DO NOT operate switches, phones, or create sparks.
- 2Leave the building immediately.
- 3Call gas company emergency line from outside.
- 4Do not re-enter until cleared by gas company.
Tighten Gas Fitting
$0-5 (Certified Pro Only)- 1Gas work requires a licensed professional in most jurisdictions.
- 2Pro applies gas-rated pipe compound or Teflon tape to threads.
- 3Leak tested with gas detector or soap bubble solution.
Replace Gas Flex Line
$20-50 parts / $100-200 Pro- 1Turn off gas supply to appliance.
- 2Disconnect old flex line.
- 3Install new CSA-approved flex connector of proper size.
- 4Leak test all connections before turning on gas.
When to Call a Professional
If you smell gas, leave immediately. Do not use phones, light switches, or anything that can spark.
Gas leaks can cause explosion and carbon monoxide poisoning.
DIY gas repair is illegal in most jurisdictions and extremely dangerous.
Never use non-approved materials (rubber hose, copper tubing) for gas connections.
How to Prevent It
Have gas appliances professionally inspected annually.
Install CO detectors on every level of your home.
Replace gas flex connectors every 10-15 years.
Know where your gas shutoff valve is and how to use it.
Gas Safety: What Every Homeowner Must Know
Natural gas has no smell — the rotten egg odor is mercaptan, an additive specifically so you can detect leaks. If you smell it: leave immediately, no switches, no phones inside, call gas company from outside.
Gas work requires a licensed professional in most jurisdictions. Even tightening a fitting requires proper leak testing and often a permit. DIY gas work is illegal in many areas and genuinely dangerous.
Carbon monoxide (CO) is the invisible killer — odorless, colorless. Install CO detectors on every level. Have gas appliances inspected annually. Replace flex connectors every 10-15 years.
Frequently Asked Questions
Leave immediately. Don't flip switches or use phones inside. Call gas company from outside. Don't re-enter until cleared.
Professional: gas leak detector. DIY soap test: mix dish soap with water, brush on fittings, watch for bubbles. Never use a flame.
In most jurisdictions, gas work requires a licensed plumber or gas fitter. Even minor work often requires a permit and inspection.
Simple fitting tightening: $100-200. Line replacement: $300-1,500. Underground line: $2,000-5,000+.