How do I clean air vents and return grilles?

Most vent and grille cleaning is a vacuum-and-wash job you can do with a screwdriver and a sink: vacuum the face of each cover, take it off, wash it in warm soapy water, let it dry and put it back. A grey film on a return grille does not mean the ducts are dirty. EPA says it is normal for the return registers to get dusty as dust-laden air is pulled through the grate,^[1] and that the registers can be easily vacuumed or removed and cleaned.^[1]

Supply registers and return grilles

Supply registers are the covers air blows out of, usually with louvers you can open and close. Return grilles are the covers where air is pulled back to the furnace or air handler; they are often larger, with fixed slats, and they collect dust faster because they face the incoming air.

Some return grilles hold the system's filter behind a hinged face. ENERGY STAR notes that, depending on the system, your filter may be located in the duct system versus the heating and cooling equipment itself.^[2] If yours is, cleaning the grille and changing the filter are one job.

What you need

• A vacuum with a brush attachment. EPA suggests a high efficiency vacuum (HEPA) cleaner or the highest efficiency filter bags your vacuum cleaner can take,^[1] and warns that Vacuuming can increase the amount of dust in the air during and after vacuuming as well as in your ducts.^[1] Turning the system off first keeps that dust out of the return.
• A screwdriver that fits the cover screws, and a cup to keep them in.
• Dish soap, a soft brush (an old toothbrush works on narrow slats) and a couple of towels.
• A damp cloth for the duct lip and the wall or floor around the vent. Dampening the cloth helps keep settled dust from going back into the air.^[4]
• A new filter of the right size, if a return grille holds one.

Before you start in an older house

Two materials call for a lighter touch.

Paint. If your home was built before 1978, it is more likely to have lead-based paint.^[5] Treat any old paint in the house as possibly lead, including the paint on old metal registers. EPA's advice for cleaning in a home that may have lead paint is not to use steel wool, scouring pads or abrasive cleaners,^[5] so wash painted covers gently and never sand or scrape them to make them look new.

Insulation around the boot. EPA tells duct cleaners to check that there are no asbestos-containing materials (e.g., insulation, register boots, etc.)^[1] before they start. If the boot behind a cover is wrapped in old, crumbling insulation, leave it alone. If you suspect material contains asbestos, don't touch it.^[6]

How far into the duct to go

Clean the cover and the lip of the duct you can reach by hand, and stop there. A household vacuum cannot clean a duct run; professional duct cleaning uses specialized tools to dislodge dirt and other debris in ducts, then vacuum them out with a high-powered vacuum cleaner.^[1]

Keep water out of the ductwork. EPA is plain about it: Steam cleaning and other methods involving moisture should not be used on any kind of duct work.^[1] Wring the cloth out well, and let washed covers dry completely before they go back. Skip disinfectant sprays as well: No chemical biocides are currently registered by EPA for use in internally-insulated air duct systems.^[1]

While the cover is off, look at the joint where the metal duct boot meets the floor, wall or ceiling. ENERGY STAR says these connections should be well sealed, and adds: These are common locations to find leaks and disconnected ductwork.^[3] At a return grille, a gap there lets the system pull dusty air from inside the wall or floor. ENERGY STAR's do-it-yourself approach is sealing air leaks using mastic sealant or metal tape,^[3] with one rule: Never use duct tape, as it is not long-lasting.^[3] If the boot has come loose from the duct, that is a repair rather than a cleaning job.

Keeping vents clean longer

• Mind the filter. ENERGY STAR's guidance is to Check your filter every month,^[2] especially in heavy heating and cooling months, and to Change your filter if it's dirty—or at least every three months.^[2] Our guide to filter ratings covers which one to buy.
• Check the fit. Make sure air cannot bypass filters through gaps around the filter holder.^[1] Dust that slips past the filter ends up on the registers and in the ducts.
• Protect vents during projects. During sanding, drywall work or other dusty renovation, EPA says to seal off supply and return registers and do not operate the heating and cooling system until after cleaning up the dust.^[1]
• Leave them open to the room. EPA's general advice is to be careful not to block air vents or grilles,^[7] which also keeps furniture from trapping dust against them.

Stop and call a pro if

• Dust or debris blows out of the supply registers when the system starts. That is one of the situations where EPA suggests duct cleaning: when particles are actually released into the home from your supply registers.^[1]
• You see growth or smell mustiness inside the duct. EPA's other reasons to clean include substantial visible mold growth inside hard surface (e.g., sheet metal) ducts,^[1] and it warns that if the insulation gets wet or moldy it cannot be effectively cleaned and should be removed and replaced.^[1]
• There are droppings, nests or insects. Ducts are infested with vermin^[1] is the third of EPA's reasons, and the entry point needs sealing too.
• The insulation around a boot is damaged and might contain asbestos.
• The duct is loose, crushed or disconnected behind the register.
• The marks are black and greasy rather than grey and you heat with a fuel-burning furnace. Read why black dust shows up around vents, and have a licensed HVAC technician look at the furnace. EPA recommends that a fuel burning furnace, stove or fireplace be inspected for proper functioning and serviced before each heating season to protect against carbon monoxide poisoning.^[1]

Related answers

If you are weighing a whole-system cleaning, start with whether air duct cleaning is worth it and how often ducts need cleaning, and learn the warning signs of a duct cleaning scam. Loclis lists DPOR-licensed businesses with their licence number and class: browse duct cleaning services, HVAC businesses in Blacksburg, or all heating and cooling answers.

If a vent has turned out to need more than a wash, describe the job once and local businesses quote it.