A furnace maintenance checklist

A forced-air furnace needs two kinds of care: simple routine tasks that an owner or building staff can do, such as changing filters and keeping vents clear, and an annual service by a licensed gas technician who checks combustion, venting and safety controls. This checklist sets out both, so nothing gets missed between visits.

Furnaces heat most Canadian houses and many small commercial and multi-unit buildings. A well-maintained furnace runs more efficiently, breaks down less often and, most importantly, vents combustion gases safely outside. The checklist below applies to typical gas-fired forced-air furnaces. Always follow the manufacturer's instructions for your equipment.

Routine tasks for owners and building staff

Monthly during the heating season

• Check the filter and replace it when dirty, or on the schedule the manufacturer recommends. Note the size and direction of airflow on the frame.
• Make sure supply registers and return grilles are open and not blocked by furniture or storage.
• Look at the area around the furnace: no stored items, paint, solvents or laundry near it.
• Check that outdoor intake and exhaust vents on high-efficiency furnaces are clear of snow, ice and debris, especially after storms.
• Listen for new noises such as banging, squealing or rattling, and note them for the technician.
• Check the condensate drain line and pump on high-efficiency furnaces for leaks or blockages.

Seasonally

• Test smoke and carbon monoxide alarms, and replace them at the end of their service life.
• Check the thermostat's batteries and program for the season.
• Look at visible ductwork for disconnected joints or damage.
• Book the annual service before the heating season starts, when technicians are easier to schedule.

Annual service by a licensed gas technician

Only a licensed gas technician should open the burner compartment or work on gas, combustion or venting components. A good annual service typically includes:

• Inspecting the heat exchanger for cracks, holes or corrosion.
• Cleaning and inspecting burners, and checking flame appearance.
• Checking the ignition system and flame sensor.
• Testing safety controls: high-limit switch, pressure switches, rollout switches and flame safeguard.
• Measuring gas pressure and checking combustion, often with a combustion analyzer.
• Inspecting the venting system and chimney or plastic vent piping for leaks, damage and proper slope.
• Checking the blower motor, wheel and belt (if any), and cleaning the blower if needed.
• Checking electrical connections and measuring motor current.
• Confirming temperature rise across the furnace is within the manufacturer's range.
• Inspecting the condensate system on high-efficiency units.

Ask for a written service record that lists what was checked, any readings taken and any problems found.

Warning signs that need prompt attention

• Carbon monoxide alarm activations, or headaches and nausea that ease when people leave the building.
• Yellow or flickering flames, soot around the furnace or vent, or a burning smell that does not go away after the first few days of the season.
• Short cycling: the furnace turns on and off frequently.
• Uneven heating, or some rooms much colder than others.
• Water around the furnace.
• Rising gas bills without a change in use or weather.

Do not reset a furnace repeatedly after it locks out. Lockouts usually mean a safety control has detected a problem, and the cause should be found by a technician.

Filters: a quick note

The filter protects the furnace's blower and heat exchanger as well as indoor air. A higher-efficiency filter catches more fine particles, but it also restricts airflow more, and some furnaces are not designed for that. Choose a filter the manufacturer allows, and change it before it loads up. Our guide on HVAC filters and MERV ratings explains the trade-off.

For property managers with many units

In multi-unit buildings, the hardest part is consistency. Keep a list of every furnace with its location, model, age and filter size. Schedule annual service for all units at once, and track tenant access, filter changes and deficiencies. Patterns, such as several furnaces of the same age failing, help you plan replacements. Our guide to building a maintenance schedule can help.

How ehZee can help

Our mechanical system inspections include an independent look at heating equipment, venting and service records. We report findings by priority and can coordinate licensed contractors to correct them. For houses, our home inspections also cover the furnace as part of the overall review.

Common questions