Wildfire Smoke Threatens Indoor Air: Home Filtration and AC Advice

Smoke from Canadian wildfires has drifted across large parts of the United States, raising health concerns as fine particulate pollution (PM2.5) can cause short‑term and chronic respiratory problems. Health officials advise people to stay indoors and take steps to keep indoor air clean.

Experts recommend keeping windows and exterior doors closed, using a wet towel seal at door thresholds, and setting HVAC systems to recirculate mode to prevent outdoor smoke from entering. Upgrading filters to MERV‑13 or higher, or using HEPA‑rated portable air cleaners, can capture a high percentage of fine particles. When a dedicated air purifier is unavailable, a DIY box‑fan filter made from furnace filters and a fan works as an effective, low‑cost alternative, according to EPA research.

Running central or window air‑conditioning units is generally safe because most systems recirculate indoor air rather than drawing in outside air. If a system has a fresh‑air intake, it should be closed or switched to recirculate. Maintaining clean filters and avoiding the mistake of turning the AC off during smoke events helps maintain cooler, cleaner indoor environments.