CircadiaOSShort answer: in winter, set the heat to about 63–66°F for the first half of the night and let it rise 2–3°F before you wake. In summer, set the air conditioning as cool as your budget allows in the first half of the night, often 66–70°F, use a fan, keep humidity down, and let it drift a couple of degrees warmer toward morning.
The target does not change much
Common sleep guidance puts the bedroom at roughly 60–67°F (15–19°C) for adults with normal bedding (National Sleep Foundation; Cleveland Clinic). One research review puts the comfortable range a little warmer, about 66–70°F (19–21°C) (Harding et al., 2019). The body's own pattern is the same in every season: core temperature falls as you fall asleep, stays low through the first half of the night, and rises before you wake. So the best setting is a curve rather than one number, in July and in January.
| Phase | Winter (heating) | Summer (cooling) |
|---|---|---|
| Bedtime | 65–67°F | 67–70°F |
| Early night | 63–65°F | 66–69°F, plus a fan |
| Late night | 64–66°F | 67–70°F |
| Before you wake | 66–68°F | 68–71°F |
Starting points, not prescriptions. Adjust for your bedding, your body and your bill. Summer numbers run warmer because many homes cannot cool a bedroom below 68°F cheaply, and a fan makes a room feel several degrees cooler.
Winter: cool is cheap, cold mornings are the problem
- Setting back at night saves money. The U.S. Department of Energy says turning the thermostat back 7–10°F for eight hours a day can save up to about 10% a year on heating and cooling.
- Heavier bedding changes the math. A thick duvet at 63°F can be warmer against your skin than a sheet at 68°F. If you pile on blankets, you can keep the room cooler.
- Warm up before the alarm. The pre-wake rise matters most in winter, when a cold room makes getting up miserable and can wake you early.
- Heat pumps: go easy. A big overnight setback can make a heat pump call for its backup electric heat in the morning, which is expensive. Smaller steps of 2–4°F, or a thermostat with adaptive recovery, avoid that.
- Dry air. Winter heating dries the air. If you wake with a dry throat, a humidifier may help more than changing the temperature.
Summer: humidity and cost are the problem
- Humid heat is worse than dry heat. Lab studies show that heat combined with high humidity increases wakefulness and cuts deep and REM sleep more than heat alone (Okamoto-Mizuno and Mizuno, 2012). Running the AC also dries the air, which is part of why it helps.
- Use a fan. A ceiling or bedside fan does not cool the air, but moving air pulls heat off your skin so you can set the AC a little higher.
- Pre-cool the bedroom. Start cooling 45–90 minutes before bed and close blinds during the day, so the AC is not fighting a room that soaked up afternoon sun.
- Warmer nights mean shorter sleep. A large study of wearable data from 68 countries found people slept less on hotter nights, mostly by falling asleep later (Minor et al., 2022).
- Let it rise toward morning. Letting the room drift 1–3°F warmer before you wake saves some cooling cost and matches your body's natural rise.
Common mistakes
- One number from bedtime to alarm. Right at bedtime, wrong by 4 a.m.
- Reading the hallway, not the bedroom. If your thermostat is in a hallway, the bedroom can be several degrees different. A room sensor or a cheap thermometer by the bed tells you what you are actually sleeping in.
- Changing too many things at once. New sheets, new setpoint and a new fan in the same week make it impossible to tell what helped.
Where CircadiaOS fits
CircadiaOS is an iPhone app that sends a four-phase overnight schedule to the smart thermostat you already own (Nest, ecobee, Honeywell Home and 20+ more brands) every evening, timed to the sleep window you set. The shape is the same in every season: coolest in early night, warmer before you wake. You set your own floor and ceiling, you can shift the whole curve warmer or cooler, and it never goes below 63°F.
On Premium ($12.99 a month or $99.99 a year, with a 14-day free trial), it reads your wearable's sleep data and, after a 14-night starting period, changes one phase at a time and keeps only what your data supports. It does not promise a result and it does not manage your energy bill. How it works.
Questions
What should I set my thermostat to at night in winter?
About 63–66°F for the first half of the night, rising to 66–68°F before you wake, is a good starting point for most adults with normal bedding. If you use a heat pump, keep overnight setbacks small so it does not switch to expensive backup heat in the morning.
What should I set my thermostat to at night in summer?
As cool as you can reasonably afford in the first half of the night, often 66–70°F, with a fan for airflow. Keep humidity down and let the room warm a degree or two toward morning.
Is 70°F too warm for sleep?
It is warmer than most sleep guidance suggests, but with light bedding, low humidity and a fan, many people sleep fine at 70°F in summer. If you wake hot in the first half of the night, try going 2°F cooler for that part of the night only.
Does lowering the thermostat at night save money?
Yes, in heating season. The U.S. Department of Energy estimates that turning the thermostat back 7–10°F for eight hours a day can save up to about 10% a year. Heat pumps are the exception to be careful with, because large setbacks can trigger backup heat.
Should I turn the heat off at night?
Usually not completely. A room that falls well below the low 60s can wake you in the early morning and makes getting up harder. A lower overnight setpoint with a warm-up before your alarm gets most of the savings without the cold start.
Sources
- U.S. Department of Energy, Energy Saver: "Programmable Thermostats" (energy.gov).
- Okamoto-Mizuno K, Mizuno K. Effects of thermal environment on sleep and circadian rhythm. Journal of Physiological Anthropology, 2012.
- Harding EC, Franks NP, Wisden W. The temperature dependence of sleep. Frontiers in Neuroscience, 2019.
- Minor K, et al. Rising temperatures erode human sleep globally. One Earth, 2022.
- National Sleep Foundation, "Sleep tips" (thensf.org/sleep-tips).
- Cleveland Clinic, "What's the best temperature for sleep?" (health.clevelandclinic.org).
Related guides
- Best temperature for sleep — the research behind the curve.
- Smart thermostat sleep schedule — how to program the four phases by hand.
- Best smart thermostat for sleep — what matters when you choose one.
- How to sleep cooler — nine fixes for summer nights.
- Why do I wake up at 3am? — the late-night phase.