Science · Core 7
Thermal environment
Temperature shapes sleep, comfort and health.
Homes that are too cold or too hot affect far more than comfort. Temperature influences sleep, the heart and lungs, and how well people cope with illness.
Why it matters
Body temperature follows a daily rhythm. Falling core temperature in the evening, helped by heat loss through the hands and feet, is part of how the body prepares for sleep 1. The rooms we sleep and live in either help or hinder that process.
What the research shows
Cold is a bigger problem than most people think. A study of 74 million deaths across 384 locations, including Australia, found that more temperature-related deaths were attributable to cold than to heat, and that most of the burden came from moderately cold days rather than extreme ones 2.
Warmer, drier homes improve health. In a randomised community trial in New Zealand, insulating existing houses made them warmer and drier and was followed by better self-rated health, less wheezing, fewer days off school and work, and fewer GP visits, while using less energy 3. The World Health Organization recommends that homes are kept warm enough in cold seasons to protect health, with 18 °C as a commonly used threshold for the general population 4.
Heat disrupts sleep. Warm bedrooms increase wakefulness and reduce deep and REM sleep, and humid heat makes this worse 5. In community-dwelling older adults, sleep was most efficient when the bedroom was between 20 and 25 °C at night, with a 5 to 10 per cent drop in sleep efficiency as it rose from 25 to 30 °C. Individual preferences varied widely 6.
What can be done
The building does most of the work: insulation and draught sealing, external shading on east and west glass, better glazing, and cross-ventilation or night purging in summer. Ceiling fans, zoned heating and cooling, and sensible bedroom set points do the rest. Bedding and sleepwear matter more than people expect.
How we assess it
We place temperature and humidity loggers in key rooms, including overnight in bedrooms, and use thermal imaging to find gaps in insulation and air leaks. We review heating, cooling, shading and glazing, and how each room behaves across the day and seasons.
Evidence at a glance
- Well supported
Cold homes harm health, and insulating them improves health outcomes. 2,3
- Well supported
Hot bedrooms disturb sleep. 5
- Reasonable
A single ideal bedroom temperature. Useful ranges exist, but people differ considerably. 6
General information only, not medical advice. How we grade evidence.
References
- Kräuchi K. The thermophysiological cascade leading to sleep initiation in relation to phase of entrainment. Sleep Med Rev. 2007;11(6):439-51. doi.org/10.1016/j.smrv.2007.07.001 · PubMed 17764994
- Gasparrini A, Guo Y, Hashizume M, et al. Mortality risk attributable to high and low ambient temperature: a multicountry observational study. Lancet. 2015;386(9991):369-75. doi.org/10.1016/S0140-6736(14)62114-0 · PubMed 26003380
- Howden-Chapman P, Matheson A, Crane J, et al. Effect of insulating existing houses on health inequality: cluster randomised study in the community. BMJ. 2007;334(7591):460. doi.org/10.1136/bmj.39070.573032.80 · PubMed 17324975
- World Health Organization. WHO Housing and health guidelines. Geneva: WHO; 2018. www.who.int/publications/i/item/9789241550376
- Okamoto-Mizuno K, Mizuno K. Effects of thermal environment on sleep and circadian rhythm. J Physiol Anthropol. 2012;31(1):14. doi.org/10.1186/1880-6805-31-14 · PubMed 22738673
- Baniassadi A, Manor B, Yu W, Travison T, Lipsitz L. Nighttime ambient temperature and sleep in community-dwelling older adults. Sci Total Environ. 2023;899:165623. doi.org/10.1016/j.scitotenv.2023.165623 · PubMed 37474050