Air
Indoor Air Quality
IAQ
The condition of the air inside a building, described by the pollutants present in it — particles, gases, moisture, and biological material — and by how effectively ventilation and filtration keep those concentrations down.
In more detail
IAQ is not one quantity. It is a set of pollutant-specific concentrations, each with its own sources, its own health evidence, and its own control strategy. Fine particulate comes from cooking, combustion, and outdoor air. Volatile organic compounds off-gas from finishes, furnishings, and cleaning products. Carbon dioxide comes from the people in the room. Moisture comes from bathing, cooking, and the ground. Radon comes from the soil. No single device addresses all of them.
Control follows a hierarchy, and the order matters more than the equipment. Source control comes first: not installing the material, not burning the fuel, not letting the moisture in. Ventilation comes second, diluting what is left with outdoor air. Filtration comes third, removing particles from air already indoors. Air-cleaning technologies beyond filtration come last and warrant more scrutiny than they usually get, because some of them generate byproducts of their own.
Good air quality is therefore a claim about specific pollutants under specific conditions. A house with excellent filtration and no ventilation has good particle numbers and rising carbon dioxide. A house with abundant outdoor air in a wildfire region has good carbon dioxide and a particle problem. The question is always which pollutant, measured how, over what period.
Why it matters
Air is the one building input nobody opts out of — roughly 15,000 liters a day, most of it drawn indoors. That makes it the environmental exposure with the shortest path between a design decision and a physiological one. It is also the dimension where the gap between a house that looks finished and a house that performs is widest: nothing about a sealed, painted, furnished room announces its emissions or its ventilation rate. Two houses can be visually identical and differ by an order of magnitude in what their occupants breathe.
The common misunderstanding
That an air purifier is the answer to indoor air quality. A filter removes particles from air already in the room. It does nothing about carbon dioxide and little about the gases off-gassing from the cabinet beside it. Buying a purifier while running a fuel-burning range with no exhaust and no outdoor air supply solves the third problem in the hierarchy and leaves the first two untouched.
Related terms
On Compound
Where this term does real work — and where the decisions get made.
Sources
Last reviewed July 2026 by Compound Editorial. Definitions are educational and not project-specific engineering or medical advice.