ronment, focusing on amelioration of high or prolonged heat conditions. Temperature fluctuations and prolonged exposure to low temperatures may also have health consequences. Generally, warmer conditions may lower the risk of health consequences among segments of the population that have difficulty in paying for heating during winter (Curriero et al., 2002; McGeehin and Mirabelli, 2001), but it should be noted that this benefit might be offset by circumstances in which weather extremes result in the loss of power for extended periods (MMWR, 1998).

Thermal Comfort Indoors

The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) defines human thermal comfort as “the state of mind that expresses satisfaction with the surrounding environment” (ASHRAE, 2004). Although comfort is a subjective evaluation, survival and health are affected by temperature, humidity, and individual factors (such as clothing, air speed, metabolic rate, and health) related to the generation, dissipation, and retention of body heat. In addition to outdoor temperature, humidity, and solar radiation, comfort is influenced by whether a building has air conditioning and whether occupants have control over the temperature (Nicol and Humphreys, 2002). Acclimatization plays a role; people who live in areas where high heat and humidity are common are better able to tolerate such conditions than those who do not (de Dear and Brager, 1998). And thermal comfort is influenced by radiant heat transfer from surrounding objects: people near hot or cold surfaces feel warmer or cooler independently of the air temperature (EPA, 2009b).

“Typical” indoor temperature varies by season, locale, building type, and the economic circumstances of the occupants, although commercial spaces, such as offices, are often maintained at a more consistent year-round temperature than residences. ASHRAE’s Thermal Environmental Conditions for Human Occupancy Standard 55-2004 characterizes the indoor summer comfort range1 as about 74–83°F (23–28°C) and the winter comfort range2 as about 67–79°F (19–26°C), depending on the relative humidity. ASHRAE separately defines acceptable temperature ranges for naturally ventilated spaces as a function of outdoor temperatures spanning about 50–93°F (10–34°C).


1 More specifically, the range when occupants are dressed in clothing typically “worn when the outdoor environment is warm” (ASHRAE, 2004).

2 When occupants are dressed in clothing typically worn when the outdoor environment is cool.

The National Academies of Sciences, Engineering, and Medicine
500 Fifth St. N.W. | Washington, D.C. 20001

Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement