The best indoor air quality monitors of 2026: CO2, radon and particles

Open a window or boost ventilation once CO2 passes about 1,000 ppm, a sign that the room’s air isn’t being refreshed enough. Outdoor air is around 420 ppm. Bedrooms can climb well above that overnight with the door and windows shut; opening a window a crack or running your ventilation, such as an HRV if you have one, usually brings levels down. A monitor with a colour display makes the habit easy.

Yes, if it measures relative humidity: keeping indoor humidity roughly between 40 and 60% makes condensation and mould less likely. In very cold weather, you may need to stay lower to avoid condensation on windows. Watch for readings that stay above 60% after cooking, showers or drying clothes indoors, and run the range hood or bathroom fan. A monitor shows the problem but doesn’t fix it; if you rent, report persistent mould to your landlord in writing.

No, most air quality monitors measure CO2, particles, VOCs and humidity, but not carbon monoxide, and none replaces a CO alarm. Install a carbon monoxide alarm with a recognized certification mark, such as ULC or CSA, if you have a gas furnace, boiler, water heater, wood stove, fireplace or other fuel-burning appliance, or an attached garage. Requirements vary, so check the rules in your province or territory.

Yes, it’s the only way to see how much smoke actually gets into the room: lighting and refuelling a stove can briefly push indoor PM2.5 far above outdoor levels. Use the readings to check door seals and chimney draft, and to know when to ventilate. Burn only dry, seasoned wood.

Accurate enough to show trends, but quality varies widely between sensors. For CO2, choose a monitor with an NDIR or photoacoustic sensor rather than an “eCO2” estimate based on VOCs, which can be badly wrong. Laser PM2.5 sensors track peaks well but may over-read in very humid air. VOC readings are relative, so compare them over time rather than between brands.