Thermal
Operative Temperature
A single temperature combining air temperature and mean radiant temperature to describe what an occupant actually experiences. At low air speeds it can often be approximated as the average of the two.
In more detail
Operative temperature combines air temperature and mean radiant temperature into a single value representing the thermal environment a person actually experiences. It is the temperature basis ASHRAE Standard 55 uses for comfort evaluation, rather than air temperature alone.
The combination is a weighted average, and the weights depend on the relative strength of convective and radiant heat transfer at the body's surface. At the low air speeds typical of houses those two are comparable, so operative temperature can often be approximated as the simple average of air and mean radiant temperature. At higher air speeds the convective term dominates and the approximation stops holding, which is why the standard defines the weighting rather than leaving it as a rule of thumb.
Its usefulness is that it makes two different rooms comparable. A room at 72°F air with cold glass and a room at 70°F air with warm surfaces can share an operative temperature and feel alike — something air temperature alone would not predict.
Why it matters
Operative temperature is why two rooms on the same thermostat can feel different, and why a house full of glazing needs either better glazing or a different setpoint than a house without it. It also gives a way to discuss comfort in numbers when the complaint arrives in adjectives: measuring surface temperatures alongside air temperature turns this room feels cold into something addressable.
The common misunderstanding
That it is simply the average of air and radiant temperature. The approximation holds at low air speeds and stops holding when air movement becomes significant — near a supply register, with a ceiling fan running, or in a well-ventilated space — where the standard's weighting matters and the simple average misleads.
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.