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Smoke sizing

How to Size an Air Purifier for Smoke Using CADR

A smoke-specific air purifier sizing method using room volume and desired air changes per hour.

AirVerdicts take
For smoke, calculate a CFM target from room volume and ACH, then compare it with published smoke CADR where available. Add headroom if outdoor smoke infiltration is continuous.

Best for

  • Wildfire-prone areas
  • Apartment smoke infiltration
  • People comparing published smoke CADR

Watch for

  • Assuming nominal fan CFM equals smoke CADR
  • Ignoring infiltration from outdoors or adjacent units
  • Using a tiny unit in a large open plan

Calculate the room requirement

Room area × ceiling height gives volume. Multiply by desired ACH and divide by 60 for the approximate clean-air CFM target.

For 400 ft² with an 8-foot ceiling at 5 ACH, the target is about 267 CFM.

Use smoke CADR when possible

Smoke CADR measures clean-air delivery for a small-particle challenge and is commonly published alongside dust and pollen CADR. It gives a more comparable performance number than a marketing room-size headline.

If the manufacturer publishes only a generic CADR, confirm how it was measured.

Add margin for continuing infiltration

If outdoor or neighboring-unit smoke keeps entering, the purifier has to remove particles while new ones arrive. More airflow, better sealing and source control can all help.

For severe wildfire conditions, multiple units can improve distribution in larger spaces.

Use the same sizing basis across brands. Room-size claims can use different air-change assumptions. When possible, compare published CADR and calculate the airflow your room actually needs.