Regulatory Background in Canada

In Ontario, work on natural gas appliances must be performed by a contractor registered with the Technical Standards and Safety Authority (TSSA) under the Natural Gas and Propane Installation Code (CSA B149.1). In British Columbia, the BC Safety Authority licenses gas contractors under the Gas Safety Act. Alberta, Saskatchewan, and Manitoba have equivalent provincial licensing bodies.

This means that annual furnace inspection involving combustion analysis, heat exchanger access, or any connection to the gas supply line must be performed by a licensed technician. Homeowners can perform filter replacement and basic visual checks, but any service that involves opening the furnace cabinet or connecting to the gas system requires a licensed professional.

Carbon monoxide note: A cracked heat exchanger allows combustion gases, including carbon monoxide, to enter the air distribution system and circulate through the home. CO is colourless and odourless. CSA recommends a CO detector within 5 metres of each bedroom, and the Ontario Fire Code requires CO alarms adjacent to sleeping areas in homes with gas appliances. Test detectors monthly; replace units older than 7 years.

What a Homeowner Can Do

Filter Replacement

The single most frequent maintenance task is filter replacement. Furnace filters capture dust, pet dander, and airborne particles before they reach the heat exchanger and blower. A blocked filter reduces airflow, which increases heat exchanger temperature and cycling frequency, shortening component life.

Filter replacement frequency depends on filter type and household conditions:

  • 1-inch fibreglass or basic polyester filters (MERV 1–4): Replace every 30 days during active heating season
  • 1-inch pleated filters (MERV 8–11): Replace every 60–90 days
  • 4-inch media filters (MERV 10–13): Replace every 6–12 months
  • Electronic air cleaners: Clean the collection cells every 3 months according to manufacturer instructions

In households with pets, more than one occupant with allergies, or a forced-air system that also provides air conditioning in summer, shorter intervals apply. Hold the used filter up to a light source: if light does not pass through the filter medium, it is overdue for replacement regardless of the calendar interval.

Visual Inspection Before Calling a Technician

Before the annual service appointment, note the following so you can communicate it accurately to the technician:

  • Date the furnace last ran for an extended cycle (to identify if short-cycling has been occurring)
  • Any unusual sounds: metallic rattling suggests a loose panel; high-pitched squealing indicates a blower belt (on older units) or bearing wear
  • Flame visibility at the sight glass: a steady blue flame is normal; yellow or orange tips indicate incomplete combustion and require immediate attention
  • Condensate drain condition (on high-efficiency furnaces): the white plastic condensate line should be clear and draining. A blocked line causes the furnace to shut down on a secondary limit switch

What a Licensed Technician Inspects

A standard annual inspection by a licensed HVAC technician covers the following:

  1. Heat exchanger inspection: Visual and sometimes camera-based inspection of all heat exchanger surfaces for cracks, holes, or corrosion. This is the most safety-critical component of the inspection — a failed heat exchanger allows combustion products into living spaces.
  2. Combustion analysis: Using a combustion analyser at the flue outlet to measure CO, CO2, and stack temperature. These values confirm that the burner is firing efficiently and that combustion products are leaving the system, not recirculating.
  3. Burner and ignition system: Cleaning of burner ports, inspection of the hot surface igniter (or pilot assembly on older units), and test of ignition and flame sensing sequences.
  4. Gas valve and pressure: Verification that gas supply pressure at the manifold matches the rated input pressure for the appliance (typically 3.5 inches water column for natural gas).
  5. Blower motor and wheel: Inspection of the blower wheel for dust accumulation (which unbalances the wheel and increases bearing wear), and verification of motor amperage draw against nameplate rating.
  6. Flue and venting: Inspection of the entire flue assembly for corrosion, joint separation, or blockages. On PVC-vented high-efficiency furnaces, check that the plastic vent terminations outside the house are clear of snow and insect nests.
  7. Controls and safety limits: Testing of high-limit switch, pressure switches (on induced-draft furnaces), and the rollout switch to confirm shutdown occurs at the correct thresholds.

High-Efficiency vs. Mid-Efficiency Furnaces

Most furnaces installed in Canada since the mid-2000s are high-efficiency condensing units with AFUE (Annual Fuel Utilisation Efficiency) ratings above 90%. These units have two heat exchangers — a primary and a secondary — and produce condensate that must drain from the cabinet. Key differences in servicing compared to older mid-efficiency units:

  • PVC flue vent pipes require inspection for UV degradation and joint integrity, unlike metal flues on mid-efficiency units
  • Condensate drain and neutraliser (if fitted) must be inspected and cleared annually; blocked drains are the most common cause of high-efficiency furnace shutdown in Ontario winters
  • The inducer motor (draft inducer) runs continuously during a heating cycle and is a common point of failure after 10–15 years; its current draw should be verified during the annual inspection

Servicing Schedule

The recommended annual schedule for a gas furnace in a Canadian climate is as follows:

  • September: Replace furnace filter. Clean condensate drain with a solution of water and a small amount of white vinegar. Confirm that the outdoor intake and exhaust terminations are clear.
  • October: Book and complete professional annual inspection before the first extended cold period. Address any items noted by the technician before November.
  • January: Check filter condition; replace if approaching full load. Check condensate drain is flowing. Check outdoor vent terminations after any heavy snowfall event.
  • March: Final filter check at end of primary heating season. Note any performance observations from the winter for inclusion in next season's service notes.

Emergency Shutdown Procedure

If a CO detector activates, or if you detect the smell of gas (mercaptan, added by gas utilities, smells like rotten eggs or sulphur):

  1. Do not operate any electrical switches, including light switches, fans, or the furnace thermostat.
  2. Evacuate all occupants from the building immediately.
  3. Leave doors open as you exit to allow air movement.
  4. From outside, call your gas utility's emergency line (Enbridge Gas in Ontario: 1-866-763-5427; ATCO Gas in Alberta: 1-800-511-3447) and emergency services (911).
  5. Do not re-enter the building until cleared by the responding utility crew.

References and Further Reading