A Timed, Ten-Step Walk-Through You Can Finish With a Flashlight and a Phone
Credit: Homeowner.ca
There is a particular quiet to a furnace room in late September. The air is still, the unit has been idle since spring, and the space around it has usually collected a summer's worth of life: a stack of flattened boxes, the camping gear, a laundry basket that drifted a little too close. Most of us think of pre-season prep as "getting the furnace serviced," and then we wait for a technician's calendar to open up. What you are actually doing in those weeks, though, is deciding whether the room your furnace lives in is ready to hold a flame for the next six months.
The good news is that a large share of that readiness is something you can see for yourself. You don't need tools beyond a flashlight and your phone, and you don't need to remove a single panel. This article walks you through a 45-minute protocol, broken into ten steps with a minute budget for each, so you can finish it in one sitting on a Saturday morning and know exactly where you stand.
Two ground rules shape everything that follows. First, this is a look-and-note check, not a repair job: anything inside the burner or blower compartment, anything involving gas pressure, and anything to do with relighting belongs to a licensed professional. Second, each step ends with a clear "stop and call" result, so a failed check never leaves you guessing. By the end, you will have either a clean bill of health for the room or a short, specific list to hand to your technician before October arrives.
Before you set a timer, it helps to settle the one situation where the 45 minutes no longer matter. Natural gas has an added odourant that most people describe as rotten eggs or sulphur, and a leak can also show up as a hissing or whistling sound near a gas line or appliance. If you notice either while you are in the furnace room, the protocol ends right there.
The current instruction from Enbridge Gas is to leave the area immediately and call its 24-hour emergency line at 1-866-763-5427, or 911, from a safe distance. While you are leaving, don't flip light switches, don't turn appliances on or off, don't use your phone near the leak, and don't start a car in an attached garage. The utility also asks you never to assume someone else has already called.
Out west, the steps are the same in spirit. FortisBC asks residents to stop what they are doing, avoid any source of ignition, head outside while leaving the door open behind them, and then call 1-800-663-9911 or 911 once they are clear of the house.
Some older guides and contractor blogs tell you to open windows or shut the gas valve before leaving. Current utility guidance from both Enbridge Gas and FortisBC is simpler: get out first, then call from outside. Follow your own utility's instructions.
It is worth knowing, too, that a carbon monoxide (CO) alarm will not warn you about a gas leak. Enbridge says so plainly, which is why your nose and ears remain the first line of defence for this particular hazard.
Here is the whole protocol in one place. You might find it helpful to screenshot this table, or print it and bring it downstairs with a pen, since the last column doubles as your list of reasons to pick up the phone.
The minutes add up to 45, and most people will find a few steps go faster than budgeted. The venting step gets the largest share because it takes you outside, which is where many of the easy-to-miss problems hide.
Start with your flashlight and a roll of masking tape or a label maker. The first job is simply to know where the off switches are, because in a real problem you won't want to be searching for them.
Most furnaces have a service switch nearby that looks like an ordinary light switch, often mounted on a wall, a joist or the side of the unit, and often with a red or labelled cover plate. Next, trace the gas line to the appliance and find the manual shutoff valve on the pipe close to the furnace. You aren't going to touch it today; you only want to see it and label it so that a technician or firefighter can find it quickly. If a humidifier is connected to the furnace, follow its small water line back to its supply valve and label that too.
A pass here means you can reach each shutoff without moving anything heavy. If a valve is buried behind shelving or you genuinely can't tell which pipe feeds the furnace, add it to your call list rather than guessing.
This is the step that makes the biggest visible difference, and it tends to be the most satisfying. Stand back and look at the furnace and its vent pipe as if you were seeing the room for the first time.
Manufacturers are blunt about this: the Carrier installation and service manual for its 59TP6C condensing furnace says never to store flammable or combustible materials on, near or in contact with the furnace. That includes cardboard, paint cans, solvents, gasoline for the lawn mower, laundry piles and the recycling bin that migrated downstairs.
Ontario's fuels regulator frames it in similar terms, advising homeowners to maintain a clear zone around the furnace area so that nothing can catch fire from the heat. The exact minimum distances for your unit are printed on its rating plate and in its installation manual, which follow the clearance rules in CSA B149.1, the Natural Gas and Propane Installation Code. Rather than trusting a number from the internet, read the plate on your own furnace and keep storage well beyond it.
A pass looks like an open, uncluttered ring around the unit and its pipes. Stop and call if you find scorch marks, melted plastic, or discoloured paint on nearby surfaces, because those are signs of heat reaching places it shouldn't.
While you're clearing space, take a quick photo of the furnace's rating plate with your phone. It lists the model number and clearance details, and your technician will thank you for having it ready.
If your home also has a wood stove or fireplace, its venting and ash handling deserve their own attention, and our winter fireplace and wood stove safety guide covers them in detail.
Every fuel-burning appliance needs a steady supply of air to burn cleanly, and many older furnace rooms were built with grilles, louvred doors or ducted openings to provide it. The trouble is that home improvements have a way of quietly closing those openings: a new finished basement wall, a solid door replacing a louvred one, a vent covered with plastic to stop a draft.
Canadian building codes already recognize that a house's air pressure affects fuel-burning appliances. The British Columbia Building Code's ventilation section requires added make-up air for a large exhaust appliance when the home contains a vented appliance that is subject to back drafting. In plain terms, the air a furnace relies on can be pulled away by other equipment in a tightly sealed house.
For this step, walk the room and look for any opening that brings air in, whether it's a grille high on the wall, a duct ending near the floor, or louvres on the door. Confirm each is open and free of boxes, insulation or tape. A pass means everything you can see is unobstructed and nothing has changed since the furnace was installed. Stop and call if a renovation has sealed off an opening, enclosed the furnace in a smaller room, or if you've added a powerful range hood or other exhaust fan since your last service.
The filter is the one component inside the airflow path that most owners can inspect themselves, and it usually slides out of a slot near where the return duct meets the furnace. Turn the furnace off at the service switch you labelled in step 1 before you pull it.
You're checking four things. Is a filter actually there? Is it the size printed on the old filter's frame and the slot? Is the airflow arrow pointing toward the furnace? And is there a date on it, so you know when it went in? Canadian guidance on timing varies a little: Natural Resources Canada suggests changing or cleaning filters every three months or as they become loaded, while the Heating, Refrigeration and Air Conditioning Institute of Canada recommends looking at them monthly through the heating season. Put those together and you have a sensible habit: look monthly, replace when it's loaded.
A higher rating isn't automatically better for your system. The Goodman furnace installation manual warns against highly restrictive 1-inch filters that create a static pressure loss above 0.25 inches of water column, and notes that running the furnace without any filter can void warranty coverage for resulting damage. Choose the filter your manufacturer specifies and write today's date on the frame before you slide it in.
A pass looks like a clean or freshly replaced filter that fits snugly, with the arrow pointing the right way. Stop and call if the filter slot has no cover, the housing is damaged, or the old filter is soaked or crushed.
When it's time to weigh a service agreement or a replacement quote against what you find here, our guide on how to read a furnace quote in Canada walks through what a good one includes.
Every fuel-burning appliance needs a steady supply of air to burn cleanly, and many older furnace rooms were built with grilles, louvred doors or ducted openings to provide it. The trouble is that home improvements have a way of quietly closing those openings: a new finished basement wall, a solid door replacing a louvred one, a vent covered with plastic to stop a draft.
Canadian building codes already recognize that a house's air pressure affects fuel-burning appliances. The British Columbia Building Code's ventilation section requires added make-up air for a large exhaust appliance when the home contains a vented appliance that is subject to back drafting. In plain terms, the air a furnace relies on can be pulled away by other equipment in a tightly sealed house.
For this step, walk the room and look for any opening that brings air in, whether it's a grille high on the wall, a duct ending near the floor, or louvres on the door. Confirm each is open and free of boxes, insulation or tape. A pass means everything you can see is unobstructed and nothing has changed since the furnace was installed. Stop and call if a renovation has sealed off an opening, enclosed the furnace in a smaller room, or if you've added a powerful range hood or other exhaust fan since your last service.
The filter is the one component inside the airflow path that most owners can inspect themselves, and it usually slides out of a slot near where the return duct meets the furnace. Turn the furnace off at the service switch you labelled in step 1 before you pull it.
You're checking four things. Is a filter actually there? Is it the size printed on the old filter's frame and the slot? Is the airflow arrow pointing toward the furnace? And is there a date on it, so you know when it went in? Canadian guidance on timing varies a little: Natural Resources Canada suggests changing or cleaning filters every three months or as they become loaded, while the Heating, Refrigeration and Air Conditioning Institute of Canada recommends looking at them monthly through the heating season. Put those together and you have a sensible habit: look monthly, replace when it's loaded.
A higher rating isn't automatically better for your system. The Goodman furnace installation manual warns against highly restrictive 1-inch filters that create a static pressure loss above 0.25 inches of water column, and notes that running the furnace without any filter can void warranty coverage for resulting damage. Choose the filter your manufacturer specifies and write today's date on the frame before you slide it in.
A pass looks like a clean or freshly replaced filter that fits snugly, with the arrow pointing the right way. Stop and call if the filter slot has no cover, the housing is damaged, or the old filter is soaked or crushed.
When it's time to weigh a service agreement or a replacement quote against what you find here, our guide on how to read a furnace quote in Canada walks through what a good one includes.
If your furnace is a high-efficiency condensing model, which you can usually tell by the white or grey plastic vent pipes rather than a metal flue, it produces water as part of normal operation. That water travels through a small trap and drain line, sometimes into a condensate pump that lifts it to a floor drain or laundry tub.
Natural Resources Canada lists the condensate drain among the items a contractor should check each fall, pointing out that a plugged drain can cause water damage in the house. Your job is the visible part: follow the clear or white tubing from the furnace to wherever it ends. Make sure the lines are connected, not kinked, and not dripping at the joints. If there's a condensate pump, check that its reservoir isn't brimming and that it's plugged in.
Then shine your flashlight on the floor under and around the furnace. A pass is a dry floor with no rust rings or mineral stains. Stop and call if you see pooling water, rust on the cabinet or the floor, or a pump that won't switch on. Lennox's owner manual adds a firm rule worth remembering: do not use a furnace if any part of it has been underwater, which matters in basements that took on water this summer.
Venting is where this check earns its keep, so it gets the biggest share of your time. Start indoors. Follow the vent pipe from the top of the furnace to where it leaves the house, looking at every joint. On a condensing furnace, the Carrier manual specifies that vent and combustion air piping slope downward toward the furnace, so that condensation drains back rather than pooling. You're looking for pipe that is continuous, supported, and gently angled back toward the unit, with no gaps, cracks or sagging runs.
If your home has a metal vent connector running to a chimney, the same principle applies: joints should be snug, and the connector should never be pulled apart or resting on something. Soot, rust streaks or scorch marks around any joint are a clear signal to stop and call.
Now head outside with your flashlight. Many high-efficiency furnaces vent through the side wall of the house, and Enbridge Gas has warned that these exhaust vents often extend out of the side of a home as low as one foot above ground, where shovelling, snowblowing or heavy snowfall can bury them without anyone noticing. A blocked vent can let carbon monoxide build up indoors.
Look at both the exhaust and intake pipes (on many units they sit side by side). Clear away leaves, wasp nests, garden décor and anything you plan to stack there over winter. Manufacturer installation manuals commonly call for terminations to sit at least 30 centimetres (12 inches) above the highest expected snow level or grade, whichever is greater, so think honestly about how deep the drifts get in that spot.
If your furnace is a high-efficiency condensing model, which you can usually tell by the white or grey plastic vent pipes rather than a metal flue, it produces water as part of normal operation. That water travels through a small trap and drain line, sometimes into a condensate pump that lifts it to a floor drain or laundry tub.
Natural Resources Canada lists the condensate drain among the items a contractor should check each fall, pointing out that a plugged drain can cause water damage in the house. Your job is the visible part: follow the clear or white tubing from the furnace to wherever it ends. Make sure the lines are connected, not kinked, and not dripping at the joints. If there's a condensate pump, check that its reservoir isn't brimming and that it's plugged in.
Then shine your flashlight on the floor under and around the furnace. A pass is a dry floor with no rust rings or mineral stains. Stop and call if you see pooling water, rust on the cabinet or the floor, or a pump that won't switch on. Lennox's owner manual adds a firm rule worth remembering: do not use a furnace if any part of it has been underwater, which matters in basements that took on water this summer.
Venting is where this check earns its keep, so it gets the biggest share of your time. Start indoors. Follow the vent pipe from the top of the furnace to where it leaves the house, looking at every joint. On a condensing furnace, the Carrier manual specifies that vent and combustion air piping slope downward toward the furnace, so that condensation drains back rather than pooling. You're looking for pipe that is continuous, supported, and gently angled back toward the unit, with no gaps, cracks or sagging runs.
If your home has a metal vent connector running to a chimney, the same principle applies: joints should be snug, and the connector should never be pulled apart or resting on something. Soot, rust streaks or scorch marks around any joint are a clear signal to stop and call.
Now head outside with your flashlight. Many high-efficiency furnaces vent through the side wall of the house, and Enbridge Gas has warned that these exhaust vents often extend out of the side of a home as low as one foot above ground, where shovelling, snowblowing or heavy snowfall can bury them without anyone noticing. A blocked vent can let carbon monoxide build up indoors.
Look at both the exhaust and intake pipes (on many units they sit side by side). Clear away leaves, wasp nests, garden décor and anything you plan to stack there over winter. Manufacturer installation manuals commonly call for terminations to sit at least 30 centimetres (12 inches) above the highest expected snow level or grade, whichever is greater, so think honestly about how deep the drifts get in that spot.
Once winter arrives, clear snow and ice from vents with a car brush or broom. Enbridge Gas advises never scraping with a sharp tool, never kicking the pipes to break ice, and never piling snow against them.
A pass is an intact, properly sloped indoor pipe and outdoor terminations that are clear and comfortably above your usual snow line. Stop and call if any section is disconnected, sagging, cracked or stained, or if a termination sits where snow routinely buries it.
Homes with a heat pump working alongside the furnace have a parallel routine outdoors, which you'll find in our heat pump maintenance checklist for Canadian seasons.
Not every home has a furnace-mounted humidifier, so if yours doesn't, bank these four minutes. If it does, it probably spent the summer switched off, and it needs a small seasonal change to be useful again.
Many bypass humidifiers have a damper, a small lever or plate on the round duct that connects the humidifier to the furnace. The Aprilaire owner's manual for its bypass models tells owners to close that damper and shut the water supply valve during the off-season, which means the heating season is when you open both again. The same manual recommends changing the water panel, sometimes called the evaporator pad, once a year. Your model may label things differently, so check the sticker on your unit before you move anything.
It's also worth setting a sensible target. Health Canada suggests keeping indoor humidity around 30% in winter to prevent mould growth, and a small hygrometer from a hardware store makes that easy to watch. If you wake up to water streaming down the inside of your windows, the setting is too high.
A pass means the damper is in its heating position, the water is on, the pad looks fresh, and nothing is dripping. Stop and call if there's a leak, heavy mineral scale, or a damper that won't budge.
If your home has a heat or energy recovery ventilator near the furnace, it helps to understand how it moves air before you adjust anything, so our explainer on how HRV and ERV systems work is worth a read.
Now for the step that protects you after the check is done. Carbon monoxide can't be seen, smelled or tasted, and a CO alarm is the only way to detect it at home.
Where alarms go depends on where you live. In Ontario, amendments to the Fire Code that took effect on January 1, 2026, require homes with a fuel-burning appliance, a fireplace or an attached garage to have a CO alarm adjacent to each sleeping area and on every storey, including storeys without bedrooms, as the Technical Standards and Safety Authority explains. That means the level with your furnace needs one too. Ontario also requires a working smoke alarm on every storey and outside all sleeping areas.
Elsewhere, provincial rules differ, but the safety advice is consistent. Technical Safety BC recommends Canadian-certified CO alarms on every floor and near bedrooms, tested monthly and replaced every seven to ten years. Check your own province's fire code or safety authority for what is legally required where you live.
For each alarm, press and hold the test button until it sounds. Then take it down or tilt it to read the manufacture date on the back; if it's close to or past the replacement age in its instructions, add a new one to your shopping list. Look for a certification mark such as CSA or ULC on the label, and remember that hardwired alarms without a battery backup won't work during a power outage.
If a CO alarm sounds for real, don't try to find the source. Health Canada's advice is to leave immediately, call 911 or your fire department once outside, and return only after a professional has fixed the problem.
A pass means you have working, in-date alarms on the furnace level and outside every sleeping area. Stop and call if an alarm is sounding, or replace any that are missing, failing the test or past their replacement age.
While you're upstairs checking alarms, stop at the thermostat. Replace the thermostat batteries if it uses them, switch the system from cool or off to heat, and look over the schedule so it matches your household's winter routine.
Ontario's fuels regulator suggests that if a heating system seems to malfunction, you check the fuse, switch and thermostat before calling a contractor, and this is exactly why the step belongs in your routine. A pass is a responsive display set to heat. Stop and call if the screen stays blank with fresh batteries and the service switch on.
The last two minutes turn your walk-through into something useful. On your phone or on the printed table, mark each step pass or fail and add a short note, along with any photos you took. That record gives a technician a head start and gives you a baseline to compare against next fall.
Some findings should never wait for a convenient appointment. Treat these as stop-and-call results:
The 2010 Technical Safety BC bulletin on annual gas appliance servicing adds a few more signs worth noting as the season gets under way, including booming noises at start-up, persistent odours, dying house plants and condensation on the inside of windows.
Call someone you chose yourself. In Ontario, TSSA-registered fuels contractors are the only businesses that can legally do fuels work, and TSSA reminds homeowners that its inspectors never sell products or knock on doors. If someone calls or shows up claiming you need a furnace inspection, you don't need to comply; you're the one responsible for booking it, and you can verify a contractor through TSSA's online registry. In other provinces, look for a gas contractor licensed by your provincial safety authority.
Even if every step passes, the annual professional inspection still matters. The furnace's internal parts, gas pressure and heat exchanger are outside what any owner walk-through can assess, and Ontario's Fire Code places the responsibility for keeping heating appliances and flue pipes in a non-hazardous condition on the owner, including a flue inspection at least every 12 months.
If you're also planning to be away for part of the winter, our winterizing checklist for vacations and snowbird season picks up where this one leaves off.
The last two minutes turn your walk-through into something useful. On your phone or on the printed table, mark each step pass or fail and add a short note, along with any photos you took. That record gives a technician a head start and gives you a baseline to compare against next fall.
Some findings should never wait for a convenient appointment. Treat these as stop-and-call results:
The 2010 Technical Safety BC bulletin on annual gas appliance servicing adds a few more signs worth noting as the season gets under way, including booming noises at start-up, persistent odours, dying house plants and condensation on the inside of windows.
Call someone you chose yourself. In Ontario, TSSA-registered fuels contractors are the only businesses that can legally do fuels work, and TSSA reminds homeowners that its inspectors never sell products or knock on doors. If someone calls or shows up claiming you need a furnace inspection, you don't need to comply; you're the one responsible for booking it, and you can verify a contractor through TSSA's online registry. In other provinces, look for a gas contractor licensed by your provincial safety authority.
Even if every step passes, the annual professional inspection still matters. The furnace's internal parts, gas pressure and heat exchanger are outside what any owner walk-through can assess, and Ontario's Fire Code places the responsibility for keeping heating appliances and flue pipes in a non-hazardous condition on the owner, including a flue inspection at least every 12 months.
If you're also planning to be away for part of the winter, our winterizing checklist for vacations and snowbird season picks up where this one leaves off.
Once your furnace room is in good shape, it's natural to keep the momentum going through the rest of the house. The same clear-space thinking you used in step 2 applies to every room, and our room-by-room guide to hidden fire hazards makes a good companion.
Forty-five minutes is a small investment for the peace of mind of knowing your furnace room is clear, dry, well vented and watched over by working alarms. You don't need to be an expert to do it well; you just need to look carefully, write down what you see, and let a professional handle anything that doesn't pass.
About the Author
Angela Nightingale is the Senior Editor at Homeowner.ca with two decades of experience in digital publishing and content strategy. She has owned two homes, taken on her share of DIY projects, and learned what most guides fail to mention. She writes from the belief that the best home guidance comes from people who have lived through the decisions — and her goal is always to leave readers feeling confident, not overwhelmed.
For most steps you're only looking, so the furnace can stay as it is. Switch it off at the service switch before pulling the filter, and don't open any panels, since those areas are for a licensed technician.
No. Enbridge Gas notes that a CO alarm detects unsafe carbon monoxide but won't detect a natural gas leak. Rely on the rotten-egg odour or a hissing sound, and consider a separate natural gas detector if your sense of smell is weak.
Ontario's fuels regulator, Technical Safety BC and Enbridge Gas all recommend an annual inspection. Natural Resources Canada gives a minimum of every two years for gas and propane furnaces, so annual service is the safer habit.
It depends on your province. In Ontario, since January 1, 2026, homes with fuel-burning appliances, fireplaces or attached garages need a CO alarm adjacent to each sleeping area and on every storey. Check your provincial fire code if you live elsewhere.
Condensing furnaces produce water that should drain back through the pipe to the trap. Drips at joints, pipes sloping the wrong way or water pooling under the unit are worth a service call.
Manufacturer installation manuals commonly call for at least 30 centimetres (12 inches) above the highest expected snow level or grade. Your unit's manual and the local code set the exact figure, so ask your technician if drifts regularly reach the pipes.
TSSA says its inspectors don't sell products or go door-to-door, and you don't have to comply with an unsolicited demand for an inspection. You can confirm an inspector's identity by calling TSSA at 1-877-682-8772.
Health Canada suggests around 30% in winter to help prevent mould. If you see condensation running down the inside of your windows, lower the setting.
Ontario's Office of the Fire Marshal says smoke alarms wear out and should be replaced every 10 years, and Technical Safety BC suggests replacing CO alarms every seven to ten years. Always follow the date and instructions on your specific alarm.
