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The Sunday Magazine

Telemarketers pitch air duct cleaning. This scientist says don't bother

There is a big gap between the hype and the science about cleaning the air ducts in our homes, according to Jeffrey Siegel. He studies indoor air quality and is a professor in the Department of Civil and Mineral Engineering at the University of Toronto. Professor Siegel says air duct cleaning is low on the list of priorities for people who want to improve the air they breathe.
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Jeffrey Siegel, a University of Toronto professor, says air duct cleaning can actually make indoor air quality worse. (Tahiat Mahboob)

"Air duct cleaning services!" That may be the most annoying phrase in the English language. Countless Canadians, even those on the federal government's Do Not Call List, are bombarded by calls selling the service.

Air ducts are in homes and offices with forced air heating and cooling systems, and they do appear to be magnets for dust and other particulates in the air, so it may seem sensible to have them cleaned from time to time. It can cost a few hundred dollars.

There has not yet been a study that has shown that it consistently improves indoor air quality, makes things cleaner.- Jeffrey Siegel

However, according to Jeffrey Siegel, there is a disconnect between the hype and marketing behind air duct cleaning and the science. He studies indoor air quality and is a professor in the Department of Civil and Mineral Engineering at the University of Toronto. 

"There's a relatively recent review paper, where someone found 60 or 70 studies on duct cleaning and summarized what they found," Siegel told Kevin Sylvester, guest host of The Sunday Edition. "They found that duct cleaning doesn't make a difference. There has not yet been a study that has shown that it consistently improves indoor air quality, makes things cleaner. Some people say that it saves energy. There's not evidence of that."

In fact, says Siegel, air duct cleaning can be make indoor air quality worse because the process kicks up dust and other particulates that were otherwise settled in the house, and the cleaning apparatus may not pick it all up. In addition, some companies use solvents or cleaning chemicals that are not good to breathe in.

"We don't like to think about it this way, but our homes are filled with dust and bacteria and fungi and all kinds of other interesting stuff, and it's of no consequence," Siegel said. "I think that the question we really need to ask ourselves is what do we want to do to improve the health of our homes, and I would say that duct cleaning is not a very ripe target for doing that."

Professor Siegel says air duct cleaning is low on the list of priorities for people who want to improve the air they breathe. (Submitted by Jeffrey Siegel)

According to Siegel, there are some circumstances where it might be wise to have air ducts cleaned — for example, if there is a moisture problem, especially one that shows up as mould. It may also be necessary following a home renovation, if the contractor did not seal the ducts while working with drywall, wood and other building materials.

In that case, Siegel recommends asking for references from friends and hiring a reputable duct cleaner, "not someone that calls you out of the blue."

There are far more important things we can do to improve the air quality in our homes, according to Siegel, such as using an efficient range hood fan while cooking, not permitting people to smoke in the house and quickly addressing moisture problems. Dealing with a plumbing or roof leak should be a high priority.

During the interview, Siegel said there are a number of web pages that offer useful information about the air in our homes and offices. Here are some that he recommends:

From Health Canada:

Canadian Centre for Occupational Health and Safety (for workplace air quality):

The U.S. Environmental Protection Association offers information that is useful for Canadians too:

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