Before the furnace starts running every day, lift off each grille in the house, vacuum the opening as far as the hose reaches, and soak the covers in warm water with a little mild dish soap instead of scrubbing them. Then put in a fresh furnace filter. The ducts behind the grilles are a different matter: a light layer of dust in there is normal and isn't a reason to call anyone. What does need booking before winter is a furnace inspection, and a check that your carbon monoxide alarms work.
Supply register or cold-air return: find out first
A forced-air house has two kinds of openings, and they get cleaned a little differently. Supply registers push warm air into the room. Returns pull room air back to the furnace. Most people have never looked closely enough to know which is which, and it takes thirty seconds to find out.
- With the furnace fan running, hold a single tissue flat against the grille. If the tissue gets pulled in and sticks, it's a return. If it flutters away or does nothing, it's a supply.
- Supply registers are usually small, often about 10 by 25 cm, with louvres you can open and close. You'll find one or two in most rooms, under windows or along outside walls.
- Returns are bigger, have fixed slats and no damper, and there are fewer of them: often one in a hallway, one low on a wall in the living room, sometimes one high up on a stair wall.
Then switch the furnace off at the thermostat before you take anything apart, so the fan doesn't kick on and blow dust at you while the grille is off.
The grilles you'll find in a GTA house
Walk the house once with this list before you start, and set the screws from each grille in its own cup so they go back in the same holes.
| Grille | Where it usually is | How it comes off |
|---|---|---|
| Floor register | Bedrooms and living rooms, often under a window | Lifts straight out; no tools |
| Wall supply | Low on a wall, near the floor | Two screws |
| Ceiling diffuser | Finished basements and many condos | Screws; use a stable step stool and lay an old sheet underneath |
| Cold-air return | Hallways and stairwells, low on living room walls | Screws; some are hinged and hold a filter behind them |
| Kitchen and bathroom grilles | Near the stove and the shower | Lift-out or screws; these collect grease and steam, so they take the longest soak |
If a grille is painted over and won't move, don't pry it with a screwdriver. Run the vacuum brush over it where it sits and leave it for a day when you can score the paint line properly.
Washing a register the way its maker says
Most advice online says to scrub vent covers or throw them in the dishwasher. The people who make them say the opposite. The use and care sheet for grilles, registers and diffusers from Applied Applications International warns that scrubbing rubs or chips the paint off, and asks for a soak instead. Here's the whole job for one register.
- With the furnace off, lift the register out or unscrew it.
- Vacuum the opening with the brush attachment, reaching down into the boot as far as the hose goes. That's where pet hair, Lego and the odd earring end up.
- Wipe the floor or wall around the opening with a damp cloth. A dark ring on the carpet next to a floor register is dust the airflow has been dropping there for months.
- Put the cover in a sink or a tub of warm water with a little mild dish soap. Kitchen and bathroom grilles get longer, and the care sheet says to add a bit more detergent for sticky ones.
- After the soak, wipe it with a sponge. A soft toothbrush gets between the slats. Don't use a scouring pad.
- Rinse in warm water and dry it completely with a clean cloth before it goes back. A wet steel register can rust at the screw holes.
- If the register has a damper lever that sticks, this is the time to free it up. The maker suggests a silicone lubricant.
- Put it back with the same screws and open the damper.
Plain soap is all this needs. Leave bleach out of it, and if someone in the house reaches for it anyway, remember Health Canada's warning that bleach mixed with other cleaning products gives off toxic gases.
The cold-air return takes a bit more care
A return grille is big and usually held by four screws, so have someone hold it while you take the last one out. Vacuum the slats on the wall first, before you unscrew it, or the dust falls straight into the duct. Behind it you'll see a short opening and then the duct running away into the wall. Vacuum what you can reach and stop there. If your return is the hinged kind with a filter behind it, that filter is part of the furnace's job list below, not something to rinse and reuse unless the filter itself says it's washable.
Where your part of the job ends
Every so often someone with a truck offers to clean the whole duct system before winter. The US Environmental Protection Agency has looked at this for years, and its page on duct cleaning is clear:
EPA does not recommend that the air ducts be cleaned routinely, but only as needed.
The same page says there is no evidence that a light amount of household dust in ducts poses any risk to your health. It lists the times when cleaning is worth considering:
- a lot of visible mould inside hard sheet-metal ducts or on other parts of the system;
- mice or insects living in the ducts;
- ducts clogged with dust and debris, or particles actually blowing out of the supply registers into the rooms.
If one of those is what you see when the grille is off, that's work for a duct contractor, not a household cleaning. The EPA also points out that the cause has to be fixed first, usually water getting in or a leak, or the problem comes back.
When you vacuum the rest of the house, the EPA suggests a HEPA vacuum or the best filter bags your vacuum can take. An ordinary one can throw fine dust back into the air while you work.
The two furnace jobs that matter more than clean grilles
Clean registers look nice. These two things keep the house safe and the furnace working.
The first is the filter. The EPA's advice is to use the highest efficiency filter that the maker of your furnace recommends, and to change it regularly. The filter catches the dust that would otherwise settle in the ducts and on the grilles you just washed, so a fresh one at the start of the season is the cheapest part of this whole job. Write the date on the edge of the frame with a marker.
The second is an inspection. On the same page, the EPA recommends that a fuel-burning furnace, stove or fireplace be inspected and serviced before each heating season to protect against carbon monoxide poisoning. If your furnace burns natural gas, propane or oil, book it now, before the cold week when every technician in the GTA is busy.
While you're thinking about it, check the alarms. Since January 1, 2026, Ontario requires carbon monoxide alarms next to each sleeping area and on every storey of a home that has a fuel-burning appliance, a fireplace or an attached garage. The province's carbon monoxide safety page asks you to press the test button on each one every month. If you rent, the landlord installs and maintains them, and you tell the landlord when one isn't working.
Keeping them clean through the winter
- Run the vacuum brush over floor registers whenever you vacuum the room. It takes a few seconds and stops the grey build-up between the slats.
- Keep sofas, beds and long curtains off supply registers. Blocked air goes nowhere useful and the dust settles right there.
- Planning a renovation this winter? The EPA says to seal off supply and return registers during dusty work and not to run the heating until the dust is cleaned up. Drywall dust is far finer than house dust.
Steady heat also brings condensation on cold glass, so if your windows start running with water in November, our article on window sill mould and condensation covers what to do. And while the grilles are your weekend project, the rest of the house can be someone else's: our deep cleaning goes into ledges, corners, door panels and baseboards, and a regular home cleaning visit covers dusting, blinds, sills and ceiling fans, with room to name the surface that matters most to you.
