Ontario · Energy · checked September 28, 2026

Combustion safety testing in London

A combustion safety test checks that your furnace, water heater and fireplace vent their exhaust outside instead of into the house, which matters most right before and after you tighten the house up. In the London area, the main heating energy is natural gas for 61% of households.

Get matched in London → The combustion safety and spillage check
A gloved hand inserting a combustion analyzer probe into a furnace flue pipe in a basement

Cost

Included with an evaluation

Natural gas heat

61%

Homes whose furnace must vent safely

Gas distributor

Enbridge Gas

CO alarms required (existing homes)

Yes

How London is built

London's houses by when they were built Ten house shapes, one for each tenth of London's 119,295 houses. Before 1961: 25%, 1961–1990: 41%, 1991–2000: 11%, 2001 or later: 24%. Older houses glow hotter.
  • Before 1961 25%
  • 1961–1990 41%
  • 1991–2000 11%
  • 2001 or later 24%
Each house stands for one in ten of London's 119,295 houses (single-detached, semi-detached, row and duplex), drawn by when it was built. The glow shows the usual pattern: older houses tend to be leakier and less insulated. More snow in the drawing means more heating degree-days: a longer, colder heating season. Sources: Statistics Canada 2021 Census (table 98-10-0233-01), NRCan HOT2000 climate data.

Why it matters in London

In the London area, 73% of households heat mainly with a forced-air furnace; natural gas is the main heating energy for 61% of households and electricity for 24% (Statistics Canada, 2023).

The risk rises after air sealing: a tighter house plus a strong exhaust fan or dryer can pull exhaust back down a chimney. That's why advisors test for spillage during an evaluation and why it should be repeated after serious tightening.

The CO alarm rule in Ontario

Ontario's Fire Code requires CO alarms in existing homes that have a fuel-burning appliance, a fireplace or an attached garage: next to every sleeping area and, since January 1, 2026, on every storey as well.

What the check involves

  • Worst-case depressurization: exhaust fans and the dryer on, doors set to make the appliance room as negative as it gets.
  • A spillage and draft check at each appliance, with a CO reading.
  • A plan if anything fails: often a sealed-combustion appliance or a fix to the venting, done by a licensed gas or oil technician.

The combustion safety check in detail.

Great Lakes–St. Lawrence Southern Ontario and southern Quebec

What this means in London’s climate

Cold winters and hot, humid summers: seal the attic, dry the basement, plan cooling.

Why it matters here: In gas-heated homes, tightening can cause spillage from older furnaces and water heaters.

Best timing: During the blower door visit.

What else homes in London need →

Sources for this climate guide · checked October 26, 2026

NRCan-licensed service organizations serving London

A service organization is a company that Natural Resources Canada (NRCan) licenses to deliver EnerGuide evaluations; its registered energy advisors do the home visit. Energy advisors check for combustion spillage during an evaluation; fixing a venting problem is work for a licensed gas or oil technician.

Only assessments from the seven HRSP-approved organizations qualify for the $600 Home Renovation Savings rebate and its assessment-path upgrade rebates; each listing below says whether it's one of them.

Source: NRCan list of licensed service organizations, checked September 28, 2026. Call to confirm your street is covered and ask about wait times.

Programs in London

Provincial · needs an evaluation Home Renovation Savings — Home Energy Assessment path Up to $10,000 per home ($5,000 if heated with Enbridge gas), including $600 back on your two assessments, for insulation, windows, air sealing and more — if the follow-up assessment is done by December 31, 2026 Open · deadline

Combustion safety test in London: common questions

Are CO alarms required in London homes?

Ontario's Fire Code requires CO alarms in existing homes that have a fuel-burning appliance, a fireplace or an attached garage: next to every sleeping area and, since January 1, 2026, on every storey as well.

Who does combustion safety testing?

Energy advisors check for spillage during an EnerGuide evaluation. Repairs to venting or appliances are done by a licensed gas or oil technician.

I have CO alarms. Isn't that enough?

Alarms warn you once CO is already in the house. A spillage test finds a venting problem before it produces CO.

Combustion safety test near London

Combustion safety test in Waterloo79 kmCombustion safety test in Kitchener81 kmCombustion safety test in Brantford82 kmCombustion safety test in Cambridge90 kmCombustion safety test in Chatham-Kent98 km All 70 cities →

Sources

Checked September 28, 2026. Census figures are for the municipality (Ontario); climate data is NRCan's HOT2000 station London (10 km away).

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