How often should you clean air vents and registers?

Short answer

Clean the air vents and registers every 6 to 12 months. With pets, smokers or a dusty area, make it every 3 months. The registers are the metal or plastic covers over the duct openings in your floors, walls and ceilings, and the job is to pull them off, wash them, and vacuum what you can reach inside the duct. It takes 30 to 60 minutes for a whole house and costs $0 to $10 in soap.

Why it matters

Every bit of air the system moves passes through a register, and the louvers catch dust the way a window screen catches bugs. Supply registers blow dust onto the wall around them and into the room. Return grilles, which pull air back to the furnace, load up faster still, and a furry grille cuts down the air the whole system has to work with. Less return air means the blower works harder and the filter behind the grille gets dirty sooner.

There's also what lives in the first stretch of duct behind each register. Dropped crumbs, pet hair, a child's small toy, and in a floor register, whatever gets swept over it. It sits there and gets blown around every time the system starts. A yearly cleaning keeps the air coming out of the vents as clean as the air that went into the filter.

When to do it more often

Pets that shed: every 3 months. Fur mats on louvers faster than dust does.
A smoker in the house: every 3 months, because the film tar leaves on louvers holds more dust.
A dusty area, such as a home near a dirt road or a construction site: every 3 months.
A renovation inside the house: once the drywall dust is gone, clean every register before you run the system hard, and change the filter.

What you need

A screwdriver, for registers held on by screws
A vacuum with a brush attachment and, if you have one, a crevice tool
A microfiber cloth
Mild soap and warm water

Steps at a glance

Turn the system off at the thermostat so it doesn't blow dust around while you work.
Unscrew or lift each register and set it aside, keeping its screws with it.
Vacuum the duct opening as far in as the hose reaches, and wipe the lip of the duct where dust gathers.
Wash the registers in warm, soapy water, scrub the louvers with the brush, and rinse.
Dry them fully before they go back, since a damp register rusts and sheds flakes.
Screw each register back in place and open the louvers to where they were.

You're done when every register is back on, the louvers are clear, and the system runs with no dust puffing out of the vents.

Signs it's overdue

Dust streaks on the wall or ceiling around a vent, fanning out in the direction the air blows.
Visible buildup on the louvers, a gray fuzz you can scrape off with a fingernail.
A musty or dusty smell when the system first starts up each day.

DIY or pro

This is an easy job that needs no tools beyond a screwdriver and a vacuum. The washing is the slow part, and it goes faster if you collect every register in the house and wash them in one batch in the tub.

What people often mean by "cleaning the vents" is a professional duct cleaning, which runs $300 to $700 and sends brushes and a powerful vacuum through the whole duct system. Most homes don't need one. It's worth it after a major renovation, when ducts were open during construction, when you find mold or a dead animal in a duct, or when a vacuum pulls out more than dust from the first stretch. For an ordinary home with a filter that gets changed, the registers and the reachable duct are where the dirt is.

FAQ

Is it worth cleaning air vents?

Yes. Clean registers keep dust out of the rooms and keep return air flowing freely. It's a yearly job with a cheap cloth and a vacuum.

Can I wash air registers in the dishwasher?

Metal registers usually survive it, but the heat can strip paint and warp plastic ones. Warm soapy water in a tub is gentler and works as well.

Do I need professional duct cleaning?

Rarely. After a renovation, a pest problem or visible mold, yes. Otherwise cleaning the registers and changing the filter keeps the ducts clean enough.

Should I close vents in rooms I don't use?

No. Closing vents raises pressure in the ducts and makes the blower work harder. Leave them open and let the system balance itself.