How often should air ducts be cleaned?

There is no schedule for duct cleaning. EPA does not recommend that air ducts be cleaned except on an as-needed basis because of the continuing uncertainty about the benefits of duct cleaning under most circumstances.^[1] It also says plainly that Duct cleaning is not considered to be a necessary part of yearly maintenance of your heating and cooling system,^[1] which instead consists of regular cleaning of drain pans and heating and cooling coils, regular filter changes and yearly inspections of heating equipment.^[1] Clean the ducts when something specific calls for it, and keep up the maintenance that stops it from coming to that.

When the ducts do need cleaning

EPA's guide names three triggers. They are worth checking for once a year, when you change a filter or before a tune-up:

• Visible mold. There is substantial visible mold growth inside hard surface (e.g., sheet metal) ducts or on other components of your heating and cooling system.^[1]
• Pests. Ducts are infested with vermin, e.g. (rodents or insects).^[1]
• Heavy debris. Ducts are clogged with excessive amounts of dust and debris and/or particles are actually released into the home from your supply registers.^[1]

A light film of dust is not one of them: EPA notes that a light amount of household dust in your air ducts is normal.^[1] EPA does say you may consider an occasional cleaning simply because ducts get dirty over time, and adds: Provided that the cleaning is done properly, no evidence suggests that such cleaning would be detrimental.^[1] That makes it a choice, not a schedule. EPA also warns homeowners: Do not hire duct cleaners who recommend duct cleaning as a routine part of your heating and cooling system maintenance.^[1] A company that pushes a fixed cleaning schedule is selling, not diagnosing.

When one of the triggers does appear, find out why before anyone cleans. If the conditions causing the mold growth in the first place are not corrected, mold growth will recur.^[1] Our answer on whether duct cleaning is worth it covers how to choose a company, and what it costs in Virginia covers the quote.

The maintenance that keeps ducts clean

Filters

ENERGY STAR says to Check your filter every month,^[2] especially in the heavy heating and cooling months, and to Change your filter if it's dirty—or at least every three months.^[2] EPA adds to Use the highest efficiency air filter recommended by the manufacturer of your heating and cooling system,^[1] and to be sure that air cannot bypass filters through gaps around the filter holder.^[1] More on that in how often to change the furnace filter.

A yearly check-up

ENERGY STAR recommends annual pre-season check-ups and suggests you check the cooling system in the spring and the heating system in the fall.^[3] For fuel-burning equipment it is a safety step as well. EPA's indoor air guidance says to Have a trained professional inspect, clean and tune-up central heating systems (furnace, flues and chimneys) annually,^[4] and its duct guide says a fuel-burning furnace, stove or fireplace should be inspected for proper functioning and serviced before each heating season to protect against carbon monoxide poisoning.^[1]

At that visit, be sure to ask the service provider to clean cooling coils and drain pans.^[1] The cost of a visit is covered in what an HVAC tune-up costs in Virginia.

Keeping the ducts dry

Water, not dust, is what turns ducts into a cleaning job. EPA says Controlling moisture is the most effective way to prevent biological growth in air ducts,^[1] and that condensation (which occurs when a surface temperature is lower than the dew point temperature of the surrounding air) on or near cooling coils of air conditioning units is a major factor in moisture contamination of the system.^[1]

• Watch the drain pan. The presence of substantial standing water and/or debris indicates a problem requiring immediate attention.^[1]
• Seal and insulate ducts outside the living space. EPA says to Make sure ducts are properly sealed and insulated in all non-air-conditioned spaces (e.g., attics and crawl spaces),^[1] and ENERGY STAR lists among the signs of poorly performing ducts that your ducts are located in an attic, crawlspace, or the garage.^[7]
• Hold humidity down. Virginia Cooperative Extension notes that Fungi (molds) grow in air over 60% relative humidity,^[6] and EPA's target is to keep indoor humidity below 60 percent (ideally between 30 and 50 percent) relative humidity.^[5]
• Dry leaks quickly. If wet or damp materials or areas are dried 24-48 hours after a leak or spill happens, in most cases mold will not grow.^[5]
• Look after a whole-house humidifier. If the furnace has one, EPA says to operate and maintain the humidifier strictly as recommended by the manufacturer.^[1]

Dust from projects

Before sanding, drywall or demolition, 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] Between projects, vacuum and wash the grilles as described in how to clean vents and return grilles.

Stop and call a pro if

• You find mold, droppings or nests inside a duct, on the coil or in the drain pan.
• Duct insulation is wet or smells musty. EPA says if the insulation gets wet or moldy it cannot be effectively cleaned and should be removed and replaced.^[1]
• Insulation or wrap around the register boot is damaged or crumbling. Leave it alone. EPA lists asbestos-containing materials (e.g., insulation, register boots, etc.)^[1] among the things to check for, and says such materials should not be disturbed or removed except by specially trained and equipped contractors.^[1]
• Debris blows out of the supply registers when the fan starts.
• The drain pan holds standing water or water is leaking around the air handler.
• Black, greasy marks show up on registers and you heat with a fuel-burning furnace. Have a licensed HVAC technician inspect the furnace, as EPA recommends for fuel-burning furnaces before each heating season.^[1]

Getting help

If the house is dusty even though the ducts look fine, see why a house stays dusty with clean ducts. 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.

When a check turns up a real problem, describe the job once and local businesses quote it.