Guide · survive the season

Wildfire smoke indoors: the clean-room playbook

When the sky goes orange, your job is one room you can defend. Here's the sequence, from EPA guidance plus the CO₂ tension nobody mentions.

A city under an orange wildfire-smoke sky — When the sky looks like this, the plan is one defendable room.

Before the season

Pick the clean room: a bedroom you can close, few windows, ideally where you sleep.
Have filtration ready: HEPA purifier sized for that room (size it) or a box-fan + MERV-13 build.
Spare filters bought in the off-season — they sell out with the first plume.
A few N95s for unavoidable time outside.
Bookmark fire.airnow.gov.

During a smoke event, in order

Close windows and doors; windows closed beats perfect anything else.
Run the purifier on high in the clean room, door shut. Let it win one room — don't ask one machine to fight the whole house.
HVAC: set fan to recirculate ("fan on," fresh-air intake closed if you have that control), best filter installed (MERV 13 if the system allows).
Stop making particles: no frying, no candles, no vacuuming without a HEPA vacuum, obviously no smoking.
Track outdoors on the Fire & Smoke map; smoke comes in waves.

The CO₂ catch

A family sealed in one room drives CO₂ up fast — the very bands that make everyone groggy and headachy, which then gets blamed on the smoke. The playbook: filter continuously, flush briefly. When the outdoor AQI dips between waves, open up for a few minutes, exchange air, close again, let the purifier re-win the room. A CO₂ monitor and any PM-capable monitor together turn this from guesswork into a rhythm.

Your car during smoke

The one time recirculation is unambiguously right: recirc + cabin filter keeps the plume out while you drive. On long drives, flush with fresh-air mode whenever you're through the worst of it — otherwise the CO₂ math takes over.

The 48-hour kit (buy in the off-season)

Spare HEPA filter for the purifier; spare MERV-13s for the box fan.
A handful of N95s per person.
Painter's tape (leaky window edges), a rolled towel (door gaps).
A PM-capable monitor, or at least the Fire & Smoke map bookmarked on two devices.

After it clears

Flush the whole house — cross-ventilation, every window, fifteen minutes.
Damp-wipe surfaces; particles settle and re-suspend.
Check the filter: a smoke season can consume most of its life. Note the date.

Sources

US EPA — Wildfires and indoor air quality (clean-room guidance).
US EPA — DIY air cleaner research.
AirNow — Fire & Smoke Map.
Bands & actions: our AQI reference.