Wildfire Smoke Indoors: What Actually Helps

First, know what you’re dealing with

Wildfire smoke is a soup of gases and particles, but the component that drives health advisories is PM2.5 — particles under 2.5 microns. They’re small enough to slip past your nose and throat and reach the deep lung. Sensitive groups (asthma, heart and lung conditions, children, older adults, pregnancy) feel it first, but at high concentrations everyone is affected.

Before changing anything, look at actual conditions rather than the sky: our free AirAware air-quality tool shows the current AQI for your location, whether wildfire smoke is inbound over the next 72 hours, and — just as usefully — when it’s forecast to clear.

The big three moves

1. Close up the house

Windows and doors shut, obviously — but also: set window AC units to recirculate, close the fireplace damper, and skip anything that pulls outdoor air in (bath fans and range hoods, used sparingly). Older, leakier homes let in more smoke; that makes active filtration (next step) more important, not less.

2. Filter the air you’re recirculating

This is where indoor air actually gets cleaned, three ways — pick by budget and room:

• Your HVAC system, if you have forced air: put a MERV-13 filter in the return and set the fan from “auto” to “on” so it recirculates continuously. This quietly filters the whole house for the cost of a filter.
• A portable HEPA purifier sized for the room where people actually are — see choosing an air purifier for wildfire smoke for the sizing math and honest picks like the Levoit Core 300S (bedroom) or Winix 5500-2 (living room).
• A CR box — a box fan plus four MERV-13 filters, taped into a cube. In EPA chamber testing this ~$70 build cleaned smoke particles at rates comparable to commercial purifiers. Full build steps in the CR box guide.

If smoke is heavy or the house is leaky, concentrate on one clean room (usually the bedroom): door closed, purifier or CR box running, and let that room be where you spend the worst hours.

3. Time your ventilation

Houses need fresh air eventually — CO₂ and indoor pollutants build up. The move is to air out when outdoor air improves, not on a schedule. Smoke often comes in waves; the forecast chart on our tool makes the clean windows obvious.

Smaller things that still help

• Don’t add indoor smoke: no candles, incense, frying, or vacuuming without a HEPA vacuum while you’re sealed up.
• Going outside: a well-fitted N95 respirator meaningfully cuts particle exposure; cloth and surgical masks don’t, for smoke.
• Car travel: windows up, AC on recirculate; many cabin filters are decent particle filters.
• Watch the humidity: sealed houses in summer get stuffy; a purifier doesn’t dehumidify. Comfort matters for actually keeping windows shut.

Who should be extra careful

Anyone with asthma, COPD, or heart disease; children; adults over ~65; and during pregnancy. This guide is exposure-reduction, not medical advice — symptoms like chest tightness or unusual shortness of breath are a call-a-clinician matter, smoke or no smoke.

The honest bottom line

You cannot make indoor air perfect during a smoke event, and nothing on this page claims to prevent any disease. What sealed rooms plus real filtration demonstrably do is cut the PM2.5 you breathe — often dramatically — for somewhere between the cost of a furnace filter and a mid-range purifier.