MaintainlyHVAC & air quality
How often should a furnace be serviced?
Furnace annual service once a year. The commonly recommended range is every 12 months. A pro tune-up catches cracked heat exchangers and CO leaks before winter. It is seasonal work, best done in autumn / fall.
This is the once-a-year visit where someone qualified opens the furnace, measures what it is actually doing, and confirms the heat exchanger is intact. It is not a filter change and not a thermostat check. The point of it is combustion safety.
Why does an annual furnace service matter?
A pro tune-up catches cracked heat exchangers and CO leaks before winter.
What happens if you skip an annual furnace service?
A cracked heat exchanger lets combustion gases mix with the air being blown through the house. That is the mechanism behind most furnace-related carbon monoxide incidents, and it is invisible without inspection. Missed servicing also voids many manufacturer warranties.
What does the professional actually do?
- Inspects the heat exchanger for cracks, often with a camera
- Measures combustion gases and flue draught, and checks for spillage at the diverter
- Cleans the burners and the flame sensor, which is the usual cause of a furnace that lights then dies
- Tests the safety interlocks: high limit, rollout switch, pressure switch
- Checks blower amp draw and the condition of the belt or bearings
- Confirms manifold gas pressure matches the rating plate
How do you choose someone qualified?
Ask for the combustion analysis printout, not just a sticker on the side of the furnace. A service that produces no measurements has not really tested anything.
What does it take?
How do you know an annual furnace service is overdue?
- A yellow or lazy burner flame instead of a crisp blue one
- Soot marks around the furnace cabinet or the flue connections
- A CO alarm that has ever sounded, even once, even if it stopped
- The furnace lighting and dying after a few seconds, repeatedly
What changes how often you need to do it?
- Furnaces over 15 years old justify a service every year without exception
- A furnace that ran hard through an unusually cold winter has done more hours than the calendar suggests
- Rental properties are often legally required to have it done annually
When should you stop and call someone?
This entire task is the professional call. If a CO alarm sounds, leave the building first and phone the emergency gas line from outside, then arrange the service.
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Get the free appDoes this differ in the US, UK, Australia or Canada?
United States
There is no federal requirement for homeowners, though many home warranty and insurance policies expect documented annual servicing. Technicians are typically NATE certified. Landlord obligations are set at state level and vary considerably.
United Kingdom
Warm-air furnaces are uncommon and the equivalent job is the boiler service. Where gas warm-air units exist, any work on them must be carried out by a Gas Safe registered engineer, which is a legal requirement rather than a preference.
Australia
Ducted gas heaters must be serviced by a licensed gasfitter. Victoria has run sustained public safety campaigns on carbon monoxide from open-flued gas heaters following fatal incidents, and recommends testing every two years as a minimum. Book before the June cold rather than during it.
Canada
Servicing before the heating season is close to essential given how many hours furnaces run here. Gas work must be done by a licensed gasfitter, with licensing handled provincially, for example TSSA in Ontario.
Common questions
Why does an annual furnace service matter?
A pro tune-up catches cracked heat exchangers and CO leaks before winter.
What happens if you skip an annual furnace service?
A pro tune-up catches cracked heat exchangers and CO leaks before winter. Skipping it does not usually fail immediately, which is exactly why it gets forgotten: the consequence arrives months later as a repair bill rather than as an obvious fault.
Does an annual furnace service differ by country?
US/CA term 'furnace'. Schedule before heating season. AU: ducted gas heaters need a licensed gasfitter, and Victoria recommends carbon monoxide testing of open-flued heaters every 2 years.
When in the year is an annual furnace service best done?
This is seasonal work. Plan it for autumn / fall, before the weather it protects against arrives.
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