#pm25

Airthings inside, IQAir and AirNow outside. Windows stay open until AQI crosses moderate — with extra caution when PM2.5 rather than PM10 is what's driving the number.

The furnace fan run deliberately rather than only when it heats or cools, with a MERV 13 filter in the return. It is the one thing in the house that touches every cubic foot of air.