Should you get your air ducts cleaned?

Somebody will offer to clean your ducts every autumn, usually by phone, usually with a price that starts low and moves once they are in the house. It is a fair question whether it is worth it, and there is a better answer than mine available.

What the EPA actually says

The EPA's guidance on duct cleaning is unusually blunt for a government document: duct cleaning has never been shown to actually prevent health problems. It notes that dust in ducts largely adheres to the duct surfaces and does not necessarily enter the living space.

It does recommend cleaning in three specific situations:

• There is substantial visible mold growth inside the ducts or on other components of the heating and cooling system
• The ducts are infested with vermin, such as rodents or insects
• The ducts are clogged with excessive amounts of dust and debris, or particles are actually being released into the home from the supply registers

And it makes a point worth repeating: where those conditions exist, something caused them, and cleaning without fixing the cause means they come back. A duct full of mold is a moisture problem wearing a different hat.

How to check, in five minutes

Take a torch and the cover off one supply register and one return. Look at the inside face of the grille and as far down the duct as the light reaches. What you are looking for is not a film of dust, which is normal and stays put; it is visible growth, droppings, or a build-up thick enough that it is coming loose.

If a company shows you a photograph of a filthy duct, ask which duct in your house it is, and ask to see it yourself. It is a reasonable question and the answer tells you a lot.

What is worth doing instead, most years

The vent covers, the inside of the cold air return grille, and the furnace filter. That is where the dust you actually breathe is sitting, and it costs an hour rather than several hundred dollars.

• Take the return cover off and clean both sides of the grille
• Vacuum each floor vent with a crevice tool and wipe the inside lip
• Change the furnace filter before the first cold night, and note the date on the frame

In Chesterton and along the lake there is a second reason to do it before the first frost rather than after: once the furnace has been running for a month, whatever was sitting on those grilles has already been through the house.

When I would say yes

After a build or a major renovation, when drywall dust genuinely does get everywhere and does keep coming out of the registers. After a rodent problem. And when there is visible mold, in which case the duct is the symptom and the moisture is the job.

Otherwise I would rather tell you to keep the money. I clean homes; I do not clean ducts, and I am not going to pretend the two are the same thing.