Portable vs whole-house air cleaning

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Two places to filter

EPA says portable air cleaners are designed to filter the air in a single room or area, while central furnace or HVAC filters are designed to filter air throughout a home.

When an HVAC filter works

EPA says furnace and HVAC filters work to filter the air only when the system is operating. It says most HVAC systems run only when heating or cooling is needed, usually less than 25% of the time during heating and cooling seasons.

Running the fan longer

EPA says more filtration would mean running the system for longer periods, which increases electricity costs and may give less reliable humidity control in the cooling season. During wildfire smoke, EPA says to set the fan to "On" instead of "Auto" if a high-efficiency filter is installed.

Using both

EPA says HVAC filtration and portable air cleaners can be used together to provide more effective filtration.

In-duct devices

EPA says other devices that do not have filters usually fit inside the HVAC ductwork and are more common in large and commercial buildings. CARB says some in-duct devices may create ozone at unhealthy levels. Ask a professional HVAC technician before adding anything to a system.

Window and ductless units

EPA says most window air conditioners and wall-mounted ductless units are intended for temperature control rather than air filtration. It says their limited filtration is meant to keep the inside of the unit clean, not to remove fine particles from the indoor air.

Sources: EPA, Guide to Air Cleaners in the Home; EPA, Wildfires and Indoor Air Quality (IAQ); California Air Resources Board, Air Cleaner Information for Consumers.

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