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  • Andrew Heilmann, PE

Wildfire Smoke and How It Affects Your HVAC Filters: PM2.5 Explained


East Brunswick, New Jersey - June 7, 2023

PM2.5 is a term used to describe atmospheric particles that measure 2.5 microns or less. While there are obvious health concerns linked to exposure to these pollutants while outdoors, many people are wondering about the efficacy of their HVAC filters when it comes to fine particulates of this type.


Smoke from wildfires is predominantly made up of fine particulates that are typically 2.5 microns or smaller, as well as ultrafine particulates measuring less than 0.1 microns. For comparison, the average human hair measures between 50 and 70 microns in width.


MERV 13 is the minimum filtration value recommended by ASHRAE and the CDC in both residential and commercial applications. The average rate of arrestance for MERV 13 filters is:

  • ≥ 90% of particles measuring 3.0 to 10.0 microns

  • ≥ 85% of particles measuring 1.0 to 3.0 microns

  • ≥ 50% of particles measuring 0.30 to 1.0 microns

This means that 50-85% of PM2.5 and ultrafine smoke particles will be caught and trapped in MERV 13 filter media, and the balance can be expected to pass through the filters and make its way into the facility. Occupants may smell smoke or observe the carryover as a haze, particularly in buildings where HVAC systems bring in large volumes of outside air.


When PM2.5 levels are extreme, there may be some stopgap HVAC system adjustments that can alleviate smoke infiltration and help return IAQ to more acceptable levels. However, these fixes should be considered temporary and will need to be reversed when conditions improve, and owners should consult with an experienced HVAC system specialist before implementing any changes.


Extremely high levels of PM2.5 particulates cause accelerated filter loading and will result in a large decrease in expected lifespan. When these events occur, MSC strongly advises clients to inspect all HVAC system filters after smoke conditions have abated to determine whether early filter replacement will be required.


For further guidance, or if you would like to schedule a filter evaluation, please contact MSC at 973-884-5000.

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