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Cleaning makes sense in specific situations, such as mould growing inside the ducts, a rodent or insect problem, or a heavy load of dust after renovation work. Government and research sources in Canada and the United States have found little evidence that cleaning ducts on a routine schedule improves health, airflow or energy use, and they point instead to good filters and a well-maintained system.
This page explains what a proper cleaning involves, when it is worth booking, what the research says, how to spot a doubtful offer or an unneeded chemical treatment, and how filters and air exchanger care keep the air in your home clean between visits.
What professional duct cleaning involves
A thorough cleaning treats the whole air system, not only the ducts you can see. The technician opens access points in the main trunks and connects a powerful vacuum that keeps the ductwork under negative pressure, so loosened dust is pulled toward the machine instead of into the house, then works through each branch with brushes or compressed-air whips. The US Environmental Protection Agency says the vacuum should exhaust outdoors or through a HEPA filter, and that every component must be cleaned, since a dirty blower or coil can quickly soil clean ducts again.
- Supply and return ducts, including the main trunks and the branches to each room.
- Registers, grilles and diffusers, removed and washed where possible.
- The furnace or air handler blower, its housing and the drain pan.
- The cooling coil, if the system includes central air or a heat pump, cleaned with methods suited to it.
- Sealing the access openings properly and installing a new filter before the system restarts.
When duct cleaning is worth booking: mould, pests and renovation dust
The EPA suggests considering a cleaning when there is substantial visible mould inside hard ducts, when ducts are infested with rodents or insects, or when they are clogged with so much dust and debris that it blows out of the registers. Dusty renovations, such as sanding drywall or floors, often lead to that last situation, especially if the system ran during the work.
If mould is the reason, the moisture behind it has to be fixed too, or it will come back. Health Canada recommends that a qualified professional assess and clean up large areas of mould.
- Mould you can see growing inside the ducts or on other parts of the system, not just a musty smell.
- Droppings, nests, or dead insects or rodents in the ductwork.
- Dust or debris puffing out of the registers when the blower starts.
- A heavy layer of construction dust after a renovation, or when moving into a newly built or renovated home.
- Ducts that got wet, for example in a basement flood, which should be inspected because damp ducts can grow mould.
Does routine duct cleaning improve air quality? What the evidence says
Natural Resources Canada's guidance for homeowners says that duct cleaning alone won't fix airflow balancing problems and generally has little effect on the heating system or on indoor air quality. A review of the scientific evidence archived by the National Research Council Canada reached a similar conclusion: there was insufficient evidence that cleaning relieves occupants' symptoms, inadequate evidence that it improves airflow or reduces energy use, and pollutant levels can even rise after a cleaning.
The EPA takes the same line: a light layer of household dust in ducts is normal, duct cleaning has never been shown to prevent health problems, and it isn't recommended as routine maintenance. None of this makes cleaning useless. It means the decision should rest on what is actually in your ducts, ideally after a look through a register or with a camera, rather than on a calendar or an unsolicited phone call.
Choosing a duct cleaning company: pressure sales and unneeded chemical treatments
The Competition Bureau lists air duct cleaning among the services used in phone and door-to-door scams, where callers offer bargain rates and then use high-pressure tactics to force a quick decision. Its advice is simple: don't let anyone rush you, and take time to research the company first.
- Be wary of cold calls or door-knockers offering a whole-house cleaning at a price that seems too low, followed by add-ons once the crew is inside.
- Walk away from promises that cleaning will cure allergies or cut your energy bills, which the evidence doesn't support.
- Ask how the company creates negative pressure, where its vacuum exhausts, and whether it cleans the blower, the coil and the returns as well as the supply ducts.
- Turn down biocides, sanitizers or sealants unless there is a documented reason; the EPA notes that no biocide is registered in the United States for ducts insulated on the inside.
- Be cautious about claims of government certification; the EPA, for example, states that it doesn't certify or endorse duct cleaning companies.
- Ask for before-and-after photos or a camera inspection so you can see what was removed.
Furnace filters: the simplest way to keep ducts clean
The filter catches much of the dust before it can settle in the ducts, the blower and the coil. Natural Resources Canada suggests changing or cleaning furnace filters every three months, or sooner as they become loaded, which can mean more often when the system runs hard in winter and summer, during renovations or with pets in the home.
- Use the size printed on the old filter's frame and install the new one with the airflow arrow pointing toward the blower.
- Choose a filter your furnace's manual allows, because a very restrictive filter can reduce airflow.
- Keep a spare on hand so a clogged filter never stays in place for lack of a replacement.
- Cover the registers and turn the system off during dusty work such as sanding, then change the filter once the work is done.
HRV maintenance through the seasons
A heat recovery ventilator has its own filters, core and outdoor hoods, and routine care is usually within a homeowner's reach. Natural Resources Canada notes that it typically means cleaning the filters and the core and checking components as the service manual describes. CMHC suggests cleaning or replacing HRV filters every two months, and calling an HRV service technician when a more thorough cleaning is needed.
- Wash or replace the filters on the schedule in the manual.
- Vacuum the core and wash it with mild soap and water if the manual allows it.
- Clear leaves in the fall, and snow or frost in winter, from the outdoor intake and exhaust hoods.
- Check that the condensate drain flows freely before the heating season.
Duct Cleaning: frequently asked questions
How often should ducts be cleaned?
No fixed schedule is backed by evidence. Natural Resources Canada says cleaning generally has little effect on indoor air quality, and the EPA doesn't recommend it as routine maintenance. Have ducts inspected and cleaned when there is visible mould, a pest problem or a heavy build-up of dust and debris, such as after renovations.
Will duct cleaning help with allergies or dust in the house?
Not reliably. Household dust comes from many sources besides the ducts, and research hasn't shown that cleaning relieves symptoms. A good filter changed on time, regular vacuuming and humidity control usually do more.
Should I let a duct cleaner spray a disinfectant or sealant?
Only with a clear, documented reason, such as confirmed mould, and only after the ducts have been cleaned and the moisture fixed. The EPA says the effectiveness and long-term safety of sealants are unproven, and the scientific review archived by the National Research Council Canada raises health concerns about biocides, sealants and encapsulants.
Someone called offering a cheap duct cleaning. Is it a scam?
It may be. The Competition Bureau warns that fraudsters call or knock on doors offering services such as air duct cleaning at bargain rates. Don't agree on the spot, never share personal information or copies of your bills, and look the company up yourself before booking.
Should the dryer vent be cleaned at the same time?
It's a good idea if it hasn't been done in a while. Lint builds up in the dryer duct and at the outside hood, which slows drying and is a fire hazard. Many duct cleaning companies offer it, but ask whether it's included, since it is a separate job from the heating ducts.
Sources
- Natural Resources Canada: Keeping the Heat In, section 9, operating your house
- National Research Council Canada: Is ventilation duct cleaning useful? A review of the scientific evidence
- US Environmental Protection Agency: Should you have the air ducts in your home cleaned?
- Competition Bureau Canada: Service-related scams
- Competition Bureau Canada: Door-to-door scams
- Health Canada: Guide to addressing moisture and mould indoors
- CMHC: How to maintain a heat recovery ventilator
Written by the LokalMatch editorial team. Reviewed by Zubair Afzal on September 24, 2026. How we write and check our guides