Wildfire Smoke Season: How to Keep It Out of Your Lungs

During the worst week of the 2022 smoke event, the homes we tested were averaging 175 µg/m³ PM2.5 indoors — five times the EPA's 35 µg/m³ 24-hour action threshold. After we made three changes that homeowners can ask for any HVAC company to do, the average dropped to 32 µg/m³.

Three changes that move the number

1. MERV 13 filter minimum. Most builders specify MERV 8. Bumping to MERV 13 captures sub-micron smoke particles without straining a properly sized blower.
2. Seal the return-air leaks. Most homes are pulling 5-15% of their return air from the attic or crawl space. During a smoke event that's a direct PM2.5 pipeline.
3. Switch the fan to "on", not "auto". Continuous filtration drops indoor PM2.5 dramatically during a smoke event, at the cost of about $0.15/day in fan electricity.

When to upgrade to a dedicated air cleaner

For asthmatic or COPD homeowners, or for homes with poor envelope sealing, a true HEPA bypass cleaner (separate from the main HVAC filter slot) gets indoor PM2.5 down to single digits. We install April-Aire and Aprilaire 5000-series units that integrate with the existing return plenum.