Thermal comfort is a subjectively defined state of mind where an individual feels neither too warm nor too cold. For the purposes of the British Standard BS EN ISO 7730, this is ‘that condition of mind which expresses satisfaction with the thermal environment.’ A person’s thermal comfort is determined by:

Air temperature (i.e. how hot or cold indoor and outdoor spaces are at a particular point in time)

Radiant temperature (heat given off by a warm object, e.g. the sun, a radiator, an oven)

Air velocity (e.g. drafts/breezes)

Humidity (i.e. moisture in the air, e.g. from weather conditions or internal sources such as drying of clothes)

Clothing Insulation (e.g. a key element of adaptation is being able to modify clothing to improve thermal comfort)

Metabolic heat (e.g. linked to activity rate, or some illnesses and medications)

Differences in the factors above means that levels of heating and cooling required to achieve thermal comfort can vary markedly. In recognition that there is no uniformly applicable threshold of comfort, The Health and Safety Executive HSE considers that a reasonable limit is to have a minimum of 80% of building occupants thermally comfortable in a work environment (What is thermal comfort?) Differences in thermal comfort within buildings can be exploited to help satisfy different comfort levels of building users, e.g. within residential homes (see the Building Comfort for Older Age report from the University of Manchester's Conditioning Demand project project).