Did you even get those “coupons” in the mail offering a “discount” on a “service” claiming to be essential to your health and well-being, namely duct cleaning? Let me first explain my use of “air quotes”: They’re not really coupons, they’re advertisements; it’s only a discount if you know what the normal price is; and, their meaning of the word “service” is different from the one I take it to be, which is that contextual to cattle breeding.

The service for owners of forced-air heating systems costs, minimally, close to $1,000, and could be closer to $2,000 for a typical house. It involves snaking a powerful vacuum hose through your house from a noisy truck on the street, followed by several hours of poking it into your ductwork, sometimes through holes they cut into it, and sucking out any accumulated dust. They also replace the furnace air filter.

When my in-laws had it done recently between two of my visits, they asked me it I noticed anything different. I said I did not, which elicited their insistence that I should be noticing the suddenly-cleaner air I was breathing (never mind that this was a day on which the heating system was not running, and that they have a house cleaner in every week.) They also said they decided to have the ducts cleaned as a result of their neighbor getting it done (as case of keeping as clean as the Jonses?), and how they negotiated a cheaper price due to the same-trip contract. This kind of “viral marketing” is common in home services, particularly driveway repaving/sealing.

The premise of duct cleaning is an appealing one: Get rid of the ugly accumulation of dust you can reach, within the airflow of your heating/air-conditioning system, which is obviously being blown around your house every time it runs. This will make the house smell cleaner, relieve any allergies you may have, and prevent all manner of respiratory illness.

So, what’s the problem? It makes no difference! I have thought long and hard about this, and encourage you to follow my logic:

First, assume that you start with clean ducts. Next, assume there is a certain amount of dust in the house (sawdust, drywall powder, cotton fluff, pet hair/dander, exfoliated skin cells, paper fibers, and soot blown in from the outside.) Finally, assume that you, as a conscientious homeowner, replace your furnace filter yearly as recommended. What happens when you turn on your heating system?

If it’s working properly, the system pulls house air through the “return” ducts, passes it through the filter, heats it or cools it, and re-delivers it to the house through the “supply” ducts. Because it’s been passed through a filter, it is delivered with less dust than it had initially. So, it is actually cleaning your air.

“Ah,” you point out, “what happens to the dust that never makes it to the filter?” Well, it will either eventually make it to the filter, or it will stick to the sides of the return ducts, maybe even accumulate there. In either case, it never gets back into the house. And that is the key reality: Properly maintained forced-air systems do not add dust to the house, they remove it.

The duct-cleaning companies will show you pictures of return ducts caked with an inch of crud to scare you into buying. Yours don’t have an inch of crud, and even if they did, it would stay where it is. It might even “catch” more of the dust passing by than clean ducts would.

The only “bad” thing about dust in your ducts is if it accumulates to the point where it is restricting the air flow, and that is highly unlikely, even in an older home. If you’re concerned, shine a flashlight through a return grille and look. The most accumulated dust will be right near the grille, and if it’s narrowed the cross-section of the duct less than 10%, there’s nothing to worry about.

[If you have (as I do) one of those older homes with grilles right in the floor, you will get an accumulation of larger “stuff” (dead leaves, crumbs, keys, coins, etc.) that has fallen through the grille. This is reachable with your vacuum’s hose by removing the grille. If you don’t do this once in a while, you may risk some of the lighter stuff working its way farther into the ductwork and potentially clogging it.]

So, what can you do with the money you’ve saved on duct cleaning to help improve air quality? Get a HEPA (High-Efficiency, Particulate-Arresting) filter installed in place of the thin, fiberglass filter usually fitted. This will involve some sheet metal work, since the HEPA filter unit needs to be installed in the return plenum next to the furnace. Nothing larger than a few microns can pass through the HEPA filter (it won’t catch viruses, but nothing will.) And it has a much larger effective surface area than the usualy fiberglass filter, so it will last more than one season in relatively clean homes.

You can also invest in a central vacuum-cleaning system, which sucks all your vacuumed dust into a canister in the basement/utility room, venting any fine particles not caught by the filter bag out of the living area (and preferably, outdoors.) Unlike most vacuums, this can actually clean the air as you use it.

Finally, consider vacuuming your window screens once in a while, from the side facing outdoors. The screen acts as a filter, catching particulates from outdoors, which include same nasty stuff like diesel exhaust, soot, and brake-pad material.