# Cool Bedroom

[The Research](https://boddy.app/research.md) / [Sleep](https://boddy.app/sleep.md) / [Efficiency](https://boddy.app/sleep/efficiency.md) / [Excluded](https://boddy.app/sleep/efficiency/excluded.md)  
Canonical: https://boddy.app/sleep/efficiency/excluded/temperature  
Last reviewed: 2026-10-23

## What It Is

Keeping the bedroom cool at night, with the thermostat, a fan, or air conditioning.

## Why It Matters

Keeping the bedroom cool is some of the most repeated sleep advice there is, and the direction behind it holds up: a systematic review of real-world studies found that higher temperatures, measured indoors or out, were mostly linked to shorter and poorer sleep, with the effect stronger in the hottest months and days and in more vulnerable people.[1] What that review did not do is pool its studies into one estimate of how much, because they differed too much in design, in how they measured temperature and sleep, and in how they analyzed the two.[1] Boddy grades sleep advice on efficiency, the share of your time in bed spent asleep, and the evidence is very uncertain about how much a cooler bedroom changes it.

A large study that measured efficiency objectively tracked wearable users across the United States over millions of nights, and found that unusually warm nights cost a little sleep and pushed it later while efficiency barely moved.[2] That study measured the weather outside rather than the room, and its authors point out that air conditioning and insulation pull the two apart, so it cannot say what turning down your own thermostat does.[2] The systematic review adds that heat measured in the bedroom has tended to go with markedly larger effects than the same heat measured outdoors, and that among its better-conducted studies, every one that measured efficiency found higher temperatures went with less efficient sleep, by amounts too far apart to settle on one.[1] None of those studies is strong enough for us to size the effect on.

None of this says a hot bedroom is fine. If you sleep hot, cooling the room is cheap, comfortable, and a reasonable thing to keep doing. What the evidence cannot support is a number: neither a temperature to aim for nor a gain in efficiency we could ask you to expect and track. That is why it sits here rather than as advice under Efficiency.

## GRADE

- Certainty: Very Low
- Magnitude: Unknown

Magnitude here is the effect on sleep efficiency, not on lifespan.

## References

1. Chevance, G. et al. (2024). A systematic review of ambient heat and sleep in a warming climate. Sleep Medicine Reviews. https://doi.org/10.1016/j.smrv.2024.101915
2. Liao, J. et al. (2025). Impact of heat exposure on sleep health and its population vulnerability in the United States. Environment International. https://doi.org/10.1016/j.envint.2025.109942