The drawbacks of duct cleaning: what can go wrong and when to skip it

Duct cleaning has real drawbacks. You can pay for a cleaning the house did not need. A crew with weak equipment can leave more dust in the rooms than it removed. Careless work can damage fragile ducts. Some companies add chemicals you did not ask for. In an older house the work can disturb asbestos. And cleaning will not fix a leak, a moisture problem or a clogged filter. Most of these are avoidable if you decide on evidence and check how the work will be done. This guide goes through each one, with what the US EPA, CMHC and Health Canada say.

1. You can pay for something the house did not need

This is the most common drawback, and the official sources are blunt about it. The US Environmental Protection Agency's guide Should You Have the Air Ducts in Your Home Cleaned? "does not recommend that air ducts be cleaned except on an as-needed basis" and says "duct cleaning has never been shown to actually prevent health problems." A CMHC fact sheet concluded that "regular duct cleaning is probably unnecessary for most householders."

The EPA also notes that "a light amount of household dust in your air ducts is normal." If that is all there is, the cleaning changes little you can see or feel, and the money is gone.

How to avoid it. Look before you book. Lift a return grille and shine a light inside. Ask the company what it does if the ducts turn out to be clean. Our technicians photograph the trunks and the blower compartment before any work starts, and if there is nothing worth cleaning we say so then. Our guide to the signs your ducts need cleaning covers what to look for.

2. A weak vacuum can leave the house dustier

Cleaning works by loosening dust and carrying it out. If the loosening happens without enough suction, the dust goes into the rooms. The EPA puts it this way: "an inadequate vacuum collection system can release more dust, dirt and other contaminants" than if the ducts had been left alone.

The EPA's checklist for a service provider includes two lines on this. The provider should "use vacuum equipment that exhausts particles outside of the home," or "use only high-efficiency particle air (HEPA) vacuuming equipment if the vacuum exhausts inside the home."

How to avoid it. Ask where the vacuum is and where it exhausts. On a house where the truck can park close enough, our vacuum stays on the truck, so what it collects leaves the building. Every register is sealed first, which puts the whole duct system under suction from one point. If a company plans to use a portable unit indoors, ask what filtration it has. That question is fair to ask us too when we clean a condo suite, where a truck cannot be used.

3. Careless work can damage the ducts

The EPA again: "A careless or inadequately trained service provider can damage your ducts." Three things are at risk.

• Flexible duct and fibreglass duct board. These are softer than sheet metal. The EPA says to "use only soft-bristled brushes for fiberglass duct board and sheet metal ducts internally lined with fiberglass." A stiff brush or a careless air whip can tear them.
• Joints and connections. A run that was barely attached can be knocked loose, and then a room gets less air than before.
• Access openings. Connecting a vacuum to the trunks means cutting openings. The EPA expects the provider to "take care to protect the duct work, including sealing and re-insulating any access holes." Openings left unsealed leak air for years.

How to avoid it. Tell the company what your ducts are made of if you know. Ask how the access openings are closed. In our process the openings in the supply and return trunks are sealed before the final inspection.

4. Chemicals you did not ask for

Some companies sell a spray, a fog or a coating as part of the job, or as an extra once they are in the house. The EPA is cautious about all three.

• Biocides and ozone. "Little research has been conducted to demonstrate the effectiveness of most biocides and ozone when used inside ducts." The EPA adds that no products are currently registered as biocides for use on fibreglass duct board or fibreglass-lined ducts.
• Sealants. Coatings sprayed inside ducts "tend not to completely coat the duct surface," and "little is known about the potential toxicity of these products under typical use conditions." The EPA says they "should never be used on wet duct liner, to cover actively growing mold, or to cover debris in the ducts."

CMHC goes further and advises against accepting offers to fog the ducts with biocide.

How to avoid it. Ask exactly what will be applied, why, and whether you can decline. Our process includes an application of Benefect, a botanical disinfectant. If you would rather skip that step, say so when you book and we leave it out.

5. Disturbing asbestos in an older house

This one matters in the older parts of Toronto and the GTA. Health Canada's page on the health risks of asbestos says that "before 1990, asbestos was mainly used for insulating buildings and homes against cold weather and noise," and lists insulation "around hot water pipes and tanks" among the places it may still be found. It also says there are "no significant health risks" when the material is left undisturbed and in good condition.

Duct cleaning is a way of disturbing things. The EPA's checklist says a provider should "inspect the system before cleaning to be sure that there are no asbestos-containing materials" in the heating and cooling system, and that such materials "should not be disturbed or removed except by specially trained and equipped contractors."

How to avoid it. If the house was built before 1990 and there is old wrap, tape or insulation on or around the ducts and pipes, tell the company before the visit. Do not let anyone cut into or brush against it. Health Canada's advice is to "avoid disturbing materials that may contain asbestos" and to "hire a professional to test for asbestos before renovating or remodelling."

6. It will not fix what it often gets blamed for

A cleaning removes what has collected in the ducts. It does not seal a leaky duct, dry out a damp basement or replace a filter. The EPA says "prior to any cleaning, retrofitting, or replacing of your ducts, the cause or causes must be corrected." If the cause is moisture, mould returns. If the cause is a filter that has been in for a year, the dust returns. CMHC makes the plainest point: ducts cannot create dust, so clean ducts will not make a dusty house dust-free.

Our guide Is duct cleaning worth it? lists the problems that look like dirty ducts and are something else.

7. The way it is sometimes sold

The last drawback is not about ducts at all. Duct cleaning is sold heavily by phone in Ontario, the CRTC has penalised duct cleaning companies over those calls, and the cheapest offers depend on an upsell once the crew is inside. That is covered in our guide to duct cleaning calls and in the guide to GTA duct cleaning scams.

When skipping it is the right call

• You looked inside a return and a supply and found a light, even film with nothing loose.
• The ducts were cleaned properly in the last few years and nothing has changed since: no renovation, no new pets, no water, no pests.
• The house is heated by a boiler and radiators and has no ducts. It may still have a dryer vent and bathroom exhaust fans worth cleaning.
• The real complaint is one hot room, a damp smell from the basement or high humidity. Fix that first.

When the drawbacks are worth accepting

The EPA lists three cases where you should consider cleaning: substantial visible mould inside hard-surface ducts, ducts infested with rodents or insects, and ducts "clogged with excessive amounts of dust and debris." CMHC adds a newly built house where the construction clean-up is in doubt, an older house after a major renovation, and visible debris in the return registers. In those cases the debris is real, the work removes it, and the drawbacks above come down to choosing a company that does the job properly.

Six questions that keep the downside small

• Will you show me photos of the ducts before you start, and tell me if they do not need cleaning?
• Where is the vacuum, and where does it exhaust?
• Do you seal every register while the vacuum runs?
• How do you close the access openings you cut?
• What, if anything, do you spray, and can I decline it?
• Is the price for the whole house, in writing, before you arrive?

For how we answer them, see what happens on duct cleaning day and the price list.

Frequently Asked Questions

What are the drawbacks of duct cleaning?

You may pay for a cleaning the house did not need, a weak vacuum can release dust into the rooms, careless work can damage ducts, some companies apply chemicals you did not ask for, and in older houses the work can disturb asbestos. Cleaning also does not fix leaks, moisture or a clogged filter.

Can duct cleaning damage my ducts?

It can if it is done carelessly. The EPA warns that a careless or inadequately trained provider can damage your ducts. Flexible duct and fibreglass duct board are the most fragile, and access openings must be sealed afterwards.

Can duct cleaning make the house dustier?

Yes, if the vacuum is too weak or the registers are not sealed. The EPA says an inadequate vacuum collection system can release more dust and dirt than leaving the ducts alone. A vacuum that exhausts outside the home avoids this.

Is duct cleaning a waste of money?

It is when the ducts hold only a light film of ordinary dust. It is not when there is visible debris, mould, pests, or dust left by a renovation. Look inside a return before you decide.

Should I let the company spray a sanitizer?

That is your choice. The EPA says little research shows that biocides are effective inside ducts, and CMHC advises against biocide fogging. Our process includes Benefect, a botanical disinfectant, and we leave it out if you ask.

Is duct cleaning safe in a house built before 1990?

It can be, but check first for old wrap, tape or insulation on the ducts and pipes that may contain asbestos. The EPA says such material should not be disturbed except by specially trained contractors. Tell the company before the visit and have the material tested.