Service a gas furnace once a year in Ontario, before the heating season rather than after it. The visit is a combustion safety inspection as much as a performance tune-up, and nearly every manufacturer's parts warranty requires documented annual professional service to stay in force. In the GTA the useful window is late September through mid-October — our guide on when to book pre-winter maintenance walks through the calendar month by month.
Why the interval is annual and not every two years
- Combustion analysis with a calibrated meter is the only way to know what the burner is actually producing — a carbon monoxide problem gives you no warning you can smell
- Heat exchangers crack from thermal cycling, and a camera scope finds the crack long before you would notice anything in the house
- Burners foul and drift out of adjustment; a lazy, yellow-tipped flame is unburned fuel and soot in the making
- The flame signal a technician reads in microamps at the sensor drifts downward for months before the furnace actually stops lighting — catching that trend converts a January no-heat call into an October housekeeping item
- Warranty: skipping documented service can cost you coverage on a control board or heat exchanger, which are the two most expensive parts in the cabinet
When once a year isn't enough
- Furnaces past 12 years — a mid-season check of the flame signal, inducer wheel and pressure switch is cheap insurance on equipment that owes you nothing
- Homes with shedding pets or an active renovation — the filter needs attention every one to two months, not once a season
- Rental units and student houses where nobody in the building thinks of the filter as their job
- Condensing furnaces whose condensate trap and pump silt up — the float switch is the only thing between that and water on the floor
- Houses with a bypass humidifier — the evaporator pad wants replacing each fall ($20–$40) and the damper flipped at season change
What a real furnace tune-up includes
- Combustion analysis with a calibrated meter — CO, CO₂, O₂ and draft, recorded as numbers
- Heat exchanger inspection, visually and with a camera scope
- Burner removal and cleaning
- Flame sensor cleaning and a flame-signal reading
- Inducer motor and pressure switch tubing check
- Blower motor and wheel inspection, lubrication where the motor takes it
- Manifold gas pressure measured and adjusted to the rating plate
- Thermostat operation and staging verified
- Filter replacement
- Safety control testing — limit switch, flame rollout, pressure switch
- A written report with the actual measurements, not a checklist of ticks
Expect 45–90 minutes on site for a single furnace. If the quoted tune-up doesn't include combustion analysis and a written set of readings, what you are buying is a cleaning. A $50 tune-up advertised on a flyer is a lead-generation call, and the margin comes from what gets sold once the technician is in your basement. Our breakdown of what's included in a furnace tune-up lists it task by task.
What furnace maintenance costs in the GTA
Free quotes, written pricing.
- Standalone furnace tune-up: $120–$250 from a licensed GTA contractor
- Maintenance plan bundling the fall furnace visit with a spring AC visit: $150–$350 a year, plus priority scheduling and a repair discount
- What you are insuring against: a $400–$900 winter repair, at the time of year when every contractor in the city is booked
If you would pay for a standalone tune-up anyway, the plan is close to the same money for two visits — see what our HVAC maintenance plans cover.
What skipping a year actually costs
The flame sensor that costs $150–$300 to service on a scheduled October visit becomes a no-heat call on the first genuinely cold night, when every furnace in the GTA that was neglected fails within the same 48 hours. The second cost is the paper trail: when a control board fails inside its warranty and the manufacturer asks for service records, an empty file turns a covered part into a full-price one.
What you can do yourself, and where the line is
- Change the filter — a 1-inch pleated MERV 8 to 11 every 60–90 days, or a 4- or 5-inch media cabinet once or twice a season
- Keep the area around the furnace clear, and never store paint, solvents or pool chemicals near a combustion appliance
- Look at the burner flame: steady and blue, not yellow and lifting
- After snow, check that the sidewall intake and exhaust terminations are clear — a plugged intake trips the pressure switch and locks the furnace out
- Test your carbon monoxide alarms; Ontario's Hawkins-Gignac Act requires a working CO alarm adjacent to sleeping areas in any home with a fuel-burning appliance
Everything past that list — pulling burners, measuring manifold pressure, running a combustion analyser, touching gas piping — is work that only a TSSA-licensed gas technician may legally carry out in Ontario, and doing it yourself puts both your insurance and your warranty at risk. If you suspect a combustion problem, read whether a furnace can leak carbon monoxide before you do anything else.
Book your annual service
ZK Mechanical runs full furnace tune-ups with combustion analysis and written readings across Burlington, Oakville, Hamilton and the wider GTA. Book your fall service and you'll have the report in hand before the first cold snap.
Frequently asked questions
How often should a gas furnace be serviced in Ontario?
Once every heating season, and ideally before it starts. Annual is the interval manufacturers write into their warranty terms and the interval that makes combustion analysis useful, because it gives a technician a year-over-year trend on CO, draft and flame signal rather than a single snapshot. Older units, rentals and homes with pets justify a second look mid-season.
Does a brand-new furnace still need annual service?
Yes, and the first year matters most. Manufacturers require the unit registered inside their window and serviced annually for the parts warranty to hold, and the first-season visit is where an installation error shows up — manifold pressure set wrong, a vent slope that drains the wrong way, a condensate trap that was never primed. A new furnace is not a serviced furnace.
What does a real furnace tune-up include?
Combustion analysis with a calibrated meter, a heat exchanger inspection including a camera scope, burner removal and cleaning, flame sensor cleaning with a flame-signal reading, blower inspection, manifold gas pressure set to the rating plate, safety control testing, filter replacement, and a written report of the measurements. If combustion analysis is missing, what you bought is a cleaning.
How much should furnace maintenance cost in the GTA?
A standalone furnace tune-up runs $120 to $250 in the GTA and takes 45 to 90 minutes. A maintenance plan covering the fall furnace visit plus a spring AC visit runs $150 to $350 a year and adds priority scheduling and a repair discount. Treat a heavily discounted phone offer as a sales call rather than a service.
What furnace maintenance can I legally do myself?
Filters, keeping the area clear, checking that sidewall vent terminations aren't blocked by snow, looking at the flame colour and testing CO alarms are all yours. Anything touching gas piping, burners, manifold pressure or combustion is restricted in Ontario to a TSSA-licensed technician working for a registered contractor, and doing it yourself puts your home insurance and equipment warranty at risk.