How often should you clean your ducts in Ontario's changing climate?

For most Ontario homes, a full duct cleaning every three to five years is a sensible baseline. Shorten that to every two to three years if you have shedding pets or someone in the house with allergies or asthma, and book a one-time cleaning after any renovation and before you move into a new or resale home. The US EPA's position is that ducts should be cleaned as needed rather than on a fixed calendar, so the real answer depends on what your home does to its ducts between visits.

What the EPA actually says

The clearest public guidance on duct cleaning is the US Environmental Protection Agency's page Should You Have the Air Ducts in Your Home Cleaned?. It does not recommend routine cleaning on a schedule; it says cleaning should be done as needed. It lists three conditions under which you should consider having ducts cleaned:

• substantial visible mould growth inside hard-surface ducts or on other parts of the heating and cooling system;
• ducts infested with vermin, such as rodents or insects;
• ducts clogged with excessive dust and debris, or particles actually released into the home from the supply registers.

The same page notes that it is normal for return registers to get dusty, that this on its own does not mean the ducts need cleaning, and that if the underlying cause of a problem is not fixed, it is likely to recur. It also says that, provided the cleaning is done properly, no evidence suggests it would be harmful. We agree with all of that, and we build our recommendations on it rather than on a sales calendar.

The EPA page is written for a typical American home. What it does not spell out is how fast "as needed" arrives in a house that runs a furnace from October to April with the windows shut, then switches to air conditioning for the summer. That is the Ontario part of the question.

Why Ontario homes reach "as needed" sooner

In a mild climate a forced-air system gets long rests in spring and autumn. In the GTA it does not. The furnace runs through a long heating season, the air conditioner takes over for the humid months, and the shoulder seasons are short. The blower is moving air through the same ducts most days of the year, and every pass deposits a little more of whatever is in the air: fabric fibre, skin, hair, pet dander, cooking residue and whatever came in on boots and coats.

Two things make the winter half worse. Windows stay closed, so there is no dilution from outside air and everything the household produces stays in circulation. And heated indoor air is dry, which keeps dust light and airborne rather than settling. By the time the furnace shuts off in April, several months of that have been drawn through the return ducts and across the blower.

Summer brings the opposite issue. Air conditioning pulls moisture out of the air across the evaporator coil, and a dusty coil holds that moisture. That is where musty smells at start-up come from, and it is why a cleaning that includes the blower and furnace base matters more than one that only reaches the vents.

Decision table: how often for your household

These intervals are the ones we recommend from our own work across Toronto and the GTA. They are a starting point; the signs in the next section override the calendar.

If two rows apply, take the shorter interval. A home with a dog and a family member with asthma is a two-to-three-year home, not a five-year one.

Signs your ducts need cleaning now

The calendar gives you a default. These four signs tell you the default has been overtaken. If you see them, the interval does not matter. For a fuller list, read our guide to the signs your ducts need cleaning.

1. Visible dust from the registers when the furnace starts. A puff from a supply grille as the blower engages means there is loose material in the branch line, and it will keep coming until it is removed.
2. A dusty or musty smell that outlasts the first heating cycle of the season. A brief burnt-dust smell at the first furnace start in autumn is normal; the dust that settled on the heat exchanger over summer is burning off. A smell that persists for days points to the ducts, the coil or the blower.
3. Uneven airflow between rooms. If one bedroom is noticeably weaker than the rest and nothing has changed at the furnace, a blocked branch or a packed register box is a common cause.
4. Filters loading faster than they used to. If the same brand of filter now looks grey in weeks rather than months, more material is reaching the return than before. Find out why. It could be the ducts, or it could be something new in the house.

One sign that is not on the list: dusty return grilles. The EPA is explicit that return registers get dusty in normal use. Wipe them. It is only a problem if the dust is coming out of the supply side.

Timing within the year

There is no wrong month, but two windows fit the Ontario pattern. Early autumn, before the furnace starts, clears summer pollen and the dust that settled while the system was on cooling, so the first closed-window months begin clean. Early spring, after the heating season, removes what the winter put in before the air conditioner starts moving it around. If your interval is up and it is January, book it anyway. Our crews work year-round; the house is not open to the weather for more than a hose through one door, and the system is sealed at the registers while we work.

Whatever the month, change the furnace filter the day the cleaning is done, so the clean system starts with a clean filter.

What a cleaning should include if it is going to last three to five years

The interval above assumes a full cleaning, not a vent dusting. For a house that means a truck-mounted vacuum connected to the main trunks, every supply and return register sealed and then pressure-cleaned, the trunks contact-brushed, and the furnace J-channel, blower and base cleaned, with photos before and after. That is our 12-step process, and it takes about 1.5 hours on site. A condo cleaning uses a portable vacuum and compressor at the wall unit and takes about 45 minutes. A vent-only cleaning done in 45 minutes leaves the trunk and blower as they were, which is why homes that buy cheap cleanings end up thinking they need one every year.

Details of what is included for a house are on our residential duct cleaning page. Pricing is by home size, not per vent: a house under 2,000 sq ft with one furnace is $399 before HST, and repeat clients get 5 percent off the cleaning, which makes keeping to an interval a little cheaper each time. The full price list is on our duct cleaning cost page.

Not sure which row of the table you are in? Send us a few details, including pets, any recent work on the house and when the ducts were last cleaned, and we will tell you honestly whether it is time.

Frequently Asked Questions

How often should air ducts be cleaned in Ontario?

Every three to five years for a standard household. Every two to three years with shedding pets or allergy and asthma sufferers. Once after a renovation, and once before moving into a new or resale home. The EPA recommends cleaning as needed rather than on a fixed schedule, so visible dust, mould or pests override the calendar.

Does the EPA recommend duct cleaning?

The EPA does not recommend routine duct cleaning, only cleaning as needed. It says to consider cleaning when there is substantial visible mould in the ducts, a vermin infestation, or ducts clogged with excessive dust and debris. It also notes that a properly done cleaning has not been shown to be harmful.

What is the best time of year to clean air ducts in Ontario?

Early autumn before the furnace starts, or early spring after the heating season ends. Both are fine. If your interval is up in winter, book it then; the cleaning works the same in any month.

Can air ducts be cleaned in the middle of winter?

Yes. We work year-round. The vacuum hose comes in through one door, the registers are sealed while the system is cleaned, and the job takes about 1.5 hours for a house.

Do dusty return grilles mean the ducts need cleaning?

Not on their own. The EPA notes that return registers normally get dusty in use. The sign that matters is dust coming out of the supply registers, or a persistent musty smell when the system runs.

Will cleaning the ducts lower my heating bill?

We do not quote a percentage, because it depends on how restricted the blower and coil were before the cleaning. A blower wheel and coil caked with dust move less air and run longer; cleaning them restores the airflow the system was designed for. Dirty ducts alone, without a dirty blower, change less.