Your IAQ Monitor Doesn’t Measure Your House

If you have bought an indoor air quality (IAQ) monitor and set it on the coffee table, it can only tell you about the air right around it, not the whole house. The device might show good numbers for carbon dioxide, fine particles (PM2.5), volatile organic compounds (TVOC), and humidity, but that reading applies to one spot at one moment. It works much like a thermostat, which measures temperature only where it sits, not at the ceiling, the floor, or in the next room.

Air quality shifts constantly from room to room and hour to hour. Supply and return ducts, exhaust fans, ERVs and HRVs (ventilation systems that swap stale indoor air for fresh outdoor air), and portable air cleaners all change what a monitor picks up. So do everyday things like wind, temperature differences pulling air through the house (called stack effect), closed doors creating separate pockets of air, cooking, showering, cleaning, and simply how many people or pets are in a room. Because pollutants are always being added or removed somewhere in the house, the air never mixes evenly, so one monitor's reading is a snapshot of its own corner, not a verdict on the whole home.

For a homeowner, this mainly means reading a single monitor's number with some caution. A good reading in the living room does not guarantee the same air quality in a bedroom, bathroom, or basement, and a bad reading in one spot does not mean the rest of the house is affected the same way.