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PM2.5, CO2, VOCs, ozone, radon and humidity explained with the official limits.
Filter-only purifiers do not make ozone. Ozone generators are designed to, and some ionizers and other electronic purifiers make it as a byproduct. Here is how to tell which is which.
CADR is the one standardized number for how fast an air purifier cleans a room. Here is how it is measured, how to use it, why smoke CADR is the one to compare, and its blind spots.
A HEPA purifier sized for the room can reduce virus-carrying particles in the air. It cannot stop transmission on its own, and some technologies sold for germs carry risks of their own.
No single gadget measures everything. Here is the order to do it in: a radon test, CO alarms, a monitor for the everyday readings, a moisture check, and a professional when the problem calls for one.
Radon testing is cheap and simple, and the EPA recommends it for every home. Here is how to do it properly, read the result, and decide whether you need mitigation.
EPA's AQI is built for outdoor air and 24-hour averages. The AQI or score on a home monitor is a maker's translation of a live reading. Here is how to read both.
Ionizers charge particles so they stick to surfaces or clump. They can also make ozone and other byproducts, and the evidence for some newer ion technologies is thin. Here is what is known.
PM10 is every inhalable particle up to 10 micrometers; PM2.5 is the fine fraction inside it. The fine fraction is the bigger health concern, but the coarse part is the dust and pollen you can see.
PM2.5 is the particle size EPA says poses the greatest risk to health. Here are the official limits, what your monitor's number means, and what actually brings it down indoors.
EPA's answer is below 60%, ideally 30 to 50%. But mold grows where surfaces stay wet, so condensation and leaks matter as much as the room reading.
EPA's answer is 30 to 50%, never above 60%. In very cold weather, go to the low end to stop condensation. Here is the evidence and how to hit the range.
Indoor CO2 is a ventilation gauge, not a toxin at normal home levels. A good NDIR monitor tells you when a bedroom or office needs fresh air. Here is how to read it.
