Home Safety
During wildfire smoke, stay indoors with windows shut. Indoor air stays cleaner only if your home and HVAC keep smoke out — and the fixes are ordinary HVAC work: snug high-MERV filtration, sealed ducts, and the right fan settings.
Houses breathe. EPA describes outdoor smoke entering through open windows and doors, through small gaps and cracks around closed windows and doors (infiltration), and through exhaust fans or HVAC systems with a fresh-air intake. Leaky return ductwork in the attic is another possible path: leaks on the return side can draw attic air — and any smoke in it — into the system. ENERGY STAR notes that sealing ducts reduces the risk of pollutants entering ducts from dusty attics, which is why duct testing and sealing can be an air-quality repair, not just an efficiency one.
Filter ratings only tell half the story.
For homes with sensitive occupants — or in the foothill communities that see smoke most — air scrubbers and purifiers at the air handler address what media filtration misses, including odors and VOCs that make a smoky week miserable even when particle counts are managed. Whole-house solutions treat every room through the ductwork you already own; portable units help but only cover the room they sit in.
Keep windows and doors shut; run the HVAC fan (ON rather than AUTO, if smoke is heavy) so air keeps cycling through the filter; skip anything that depressurizes the house like kitchen and bath exhaust fans running for long stretches; and if your system has a fresh-air intake, know where its damper is — during heavy smoke it should be closed or filtered.
The honest answer is: the highest rating your specific blower and duct system can support without choking airflow — which we can measure. Many systems handle a well-fitted MERV 11–13 media filter comfortably; forcing a very restrictive filter into a system designed for a thin fiberglass pad can do more harm than good. It's a measurement question, not a shopping question.
Good ones genuinely help — in the room they're in, sized to that room. For whole-home coverage, filtration and purification at the air handler treats every room through the ducts you already have. Many families do both: whole-house filtration plus a portable unit in the bedroom of whoever is most sensitive.
Common paths include leaky return ducts drawing attic air in, a fresh-air intake or evaporative cooler damper that's open, and envelope leakage at doors, windows, and penetrations. A duct-leakage test checks the first one, and it's one of the more fixable paths.
Sources
Last reviewed: 2026-09-30
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