How to tell whether your house actually needs a duct cleaning

Duct cleaning gets sold hard. Flyers, cut-price coupons, phone calls offering a whole-home clean for less than the cost of a service call. So it is a fair question whether the whole thing is worth paying for, and the honest answer is that it depends entirely on what is actually in your ducts.

Here is where the evidence sits, and how to work out which side of the line your house falls on.

Does duct cleaning improve the air in my house?

Not as a general rule, no. The US Environmental Protection Agency's position is that duct cleaning has never been shown to prevent health problems, and that studies do not conclusively show that dust levels in homes rise because ducts are dirty. The reason is mechanical rather than surprising: most of the dirt that collects inside ductwork sticks to the duct surfaces and stays there rather than travelling into the rooms you live in.

Canadian guidance points the same way. Studies from Canada Mortgage and Housing Corporation, cited in federal housing guidance, found that duct cleaning does not usually change the quality of the air you breathe, and does not significantly affect airflow or heating costs.

That is worth knowing before anybody quotes you, because "it will clean the air in your home" is the single most common thing said about this service and it is not supported.

So when is duct cleaning worth paying for?

There are real cases, and they are specific. The EPA names three conditions that justify having ducts cleaned:

Substantial visible mould growth inside hard surface ducts or on other components of the heating and cooling system. Ask to be shown it. Something can look like mould without being mould, and much of a duct system cannot be seen without opening it up.

Vermin. Rodents or insects in the ductwork.

Ducts clogged badly enough that particles are actually coming out of your supply registers. Not a dusty register grille, which is normal and just needs vacuuming, but visible debris entering the room when the system runs.

To those three, add a fourth that comes up constantly in practice: a renovation. Drywall dust, sawdust and construction grit get pulled into an operating system while the work is happening, and that is a genuine one-time load of debris rather than the slow accumulation the studies are talking about.

The EPA also makes a point worth repeating: if one of those conditions exists, something caused it. Find the cause first, or it comes back.

How often should air ducts be cleaned?

There is no interval that applies to every house, and any company quoting you a universal one is quoting a sales schedule rather than a maintenance need. The EPA recommends cleaning as needed rather than routinely.

If you want a rhythm, ours is this: have a look at the system every three years or so, and closer to annually in a home with pets that shed heavily, then clean when what you find justifies it. Treat that as when to look, not as a deadline you are behind on.

Will it lower my heating bill?

Probably not by itself. The EPA notes that little evidence exists that cleaning the ducts alone improves the efficiency of the system. Some research does suggest that cleaning components like the cooling coils, fans and heat exchangers can improve efficiency and extend how long equipment lasts, which is a different job from cleaning the duct runs.

If your bills are climbing, the equipment is the better place to look. A furnace running longer than it used to, a filter nobody has changed in a year, or a heat pump with a fouled coil will all show up on a bill in a way that dusty ductwork will not.

What matters more than cleaning

If the goal is less dust in the house, two things do more work than any cleaning:

The filter. Use the highest efficiency filter your system's manufacturer recommends, change it on schedule, change it more often if it clogs, and make sure air cannot slip around the edges of the holder. This is the cheapest control you have over what circulates.

Moisture. Keeping ducts dry is the most effective way to prevent biological growth in them. Repair leaks, keep an eye on the condensate pan under the cooling coil, and make sure ductwork running through unheated space is properly sealed and insulated so it does not sweat.

One practical note for anyone renovating: seal off the supply and return registers during dusty work and leave the system off until the cleanup is done. That prevents the exact problem that sends most people looking for a duct cleaning afterward.

Is a dryer vent the same decision?

No, and this is the part of the conversation that gets least attention while mattering most.

A dryer vent is a fire safety item, not an air quality one. Lint collects in the vent run over time, lint catches easily, and it collects in the one place hot air passes through every time you run a load. The usual sign of a restricted vent is clothes needing two or three cycles to dry, because the dryer cannot push its hot wet air out of the house.

If your dryer has started taking noticeably longer than it used to, that is worth dealing with on its own terms. It is not a judgement call in the way duct cleaning is.

If you do decide to have it done

The work itself is straightforward when it is done properly, and the whole point is that the dust leaves the building rather than being stirred up and left to settle somewhere else. Done badly, an inadequate vacuum setup can put more dust into a house than leaving the ducts alone would have.

Worth asking any company, ours included:

• Show me the contamination that justifies this. Not a petri dish, the actual system.
• Does your vacuum exhaust outdoors, or does it use HEPA filtration if it exhausts inside?
• How will you protect the flooring and furnishings?
• How will you seal the access hole you cut, and re-insulate it?
• Will you clean the return side as well as the supply side?

And a few warning signs the EPA names directly. Be wary of anyone making sweeping claims about the health benefits of duct cleaning, anyone selling it as routine maintenance every house needs on a schedule, and anyone claiming to be EPA certified. The EPA does not certify, endorse or approve duct cleaning companies, so that claim can only be one thing.

Where we land on it

Most houses on a calendar do not need their ducts cleaned. Some houses very much do, and in those cases the difference between a proper job and a cheap one is whether the dust ends up outside or redistributed through your living room.

Air Comfort Systems handles duct and dryer vent cleaning across Metro Vancouver using source removal, on residential and commercial systems. If you are not sure which side of the line your house falls on, say so when you call. It is a reasonable thing not to know.

Sources: US EPA, Should You Have the Air Ducts in Your Home Cleaned?; Canada Mortgage and Housing Corporation research as cited in federal housing guidance on indoor air quality.