Home Safety
Every SoCal fire season the advice is the same: stay indoors with the windows shut. But 'indoors' is only cleaner than outside if your home and HVAC are set up for it — smoke particles are small enough to slip through gaps and straight through builder-grade filters. The good news: the fixes are ordinary HVAC work, not exotic equipment.
Houses breathe. Gaps at doors, windows, penetrations, and — most underrated — leaky return ductwork in the attic all pull outdoor air in, especially when temperature differences or the HVAC blower create pressure imbalances. During a smoke event, a return-side duct leak in the attic is essentially a smoke pipe into your living room. That's why duct testing and sealing is 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.
Usually one of three paths: leaky return ducts pulling attic air in, a fresh-air intake or evaporative cooler damper that's open, or simple envelope leakage at doors and penetrations. A duct-leakage test finds the first one — it's the most common and the most fixable.
Last reviewed: 2026-07-22
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