Thermal comfort is a personal, subjective state reflecting satisfaction with the surrounding thermal environment. Achieving a single temperature setting that pleases every adult is impossible due to the complex interplay of physiology and environmental conditions. The ongoing struggle over a thermostat highlights the challenge of defining a universal “perfect” temperature. Scientific standards offer a widely accepted range that provides comfort for the majority of people.
The Generally Accepted Temperature Range
For a typical sedentary adult wearing normal indoor clothing, the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) provides a framework for thermal acceptability. This framework defines a “comfort zone” rather than a single point. For the majority of occupied spaces, the acceptable temperature range spans from approximately 68°F (20°C) to 79°F (26°C).
This broad range is refined based on the season and the expected clothing level of the occupants. During the heating season, when individuals wear heavier clothing, the comfortable range is tighter, generally falling between 68°F (20°C) and 75°F (24°C). Conversely, in the cooling season, when clothing is lighter, acceptable temperatures shift slightly higher, typically from 73°F (23°C) to 79°F (26°C). These figures represent the operative temperature, which combines air temperature and the mean radiant temperature of surrounding surfaces.
Environmental and Personal Factors Affecting Comfort
The standard temperature range serves as a baseline, but individual comfort is influenced by six primary variables: four environmental and two personal. Environmental factors include relative humidity, which should be maintained between 30% and 65%. High humidity, especially in summer, can make a given temperature feel warmer because it limits the body’s ability to cool itself through sweat evaporation.
The mean radiant temperature is another environmental factor, referring to the temperature of surrounding surfaces like walls, windows, and floors. Sitting near a cold window in winter can cause discomfort due to heat loss from the body, even if the air temperature is set correctly. Air movement, or velocity, also plays a role, as slight air movement can be pleasant in warm conditions but can feel like an uncomfortable draft in cooler settings.
Personal factors include clothing insulation, measured in “clo” units, where higher values correspond to warmer clothing. A person wearing a winter sweater will feel comfortable at a lower temperature than someone in a summer t-shirt. The metabolic rate, or the energy the body is producing, also dictates comfort. A person performing light office work has a lower metabolic rate than someone exercising, requiring a warmer environment. Age is a further consideration, as older adults often have slower metabolism and reduced circulation, leading them to prefer temperatures a few degrees warmer than younger adults.
Setting Temperatures for Rest and Activity
The optimal temperature setting for a room changes significantly depending on whether the body is resting or engaged in activity. Nighttime temperatures should be cooler than daytime temperatures to align with the body’s natural circadian rhythm. To initiate and maintain healthy sleep, the body’s core temperature must naturally drop.
The recommended temperature for a bedroom is substantially lower than the daytime comfort zone, often suggested to be between 60°F (16°C) and 67°F (19°C). This cooler environment supports the body’s thermoregulatory process. For areas involving light physical activity or focused mental work, temperatures should be on the lower end of the general comfort range. Individuals engaging in active states generate more body heat, making a slightly cooler room more comfortable than a static, sedentary setting.
Balancing Comfort, Health, and Energy Use
Adults must navigate the trade-off between maximizing personal comfort, maintaining health, and managing energy consumption. Temperature settings outside a moderate range affect well-being; for example, keeping a home below 61°F (16°C) can increase the risk of respiratory issues. For vulnerable populations, such as the elderly, maintaining stable temperatures above 68°F (20°C) is important to reduce cardiovascular strain and other health risks.
From an energy perspective, small adjustments to the thermostat lead to significant cost savings. Energy efficiency experts often suggest a “setback” strategy, recommending that the thermostat be adjusted by several degrees when the home is unoccupied or when occupants are sleeping. Utilizing programmable or smart thermostats automatically implements these adjustments, ensuring comfort when needed while minimizing the financial and environmental impact. Minor behavioral changes, such as wearing appropriate clothing for the season, allow the thermostat to be set toward the extremes of the comfort zone, optimizing energy use.