The Science · Aircon Energy Savings

The Best Time to Switch Off Your Aircon

Not a guess, and not tied to your city's weather — this is about your own body's schedule, which runs the same way regardless of where you live.

This applies across the tropics: Singapore, Kuala Lumpur, Jakarta, Bangkok, Manila, Ho Chi Minh City, Mumbai, and other humid-climate cities — the mechanism is physiology, not geography.

Your body is already cooling itself down for you

Core body temperature isn't constant through the night — it follows a well-established circadian pattern, dropping steadily after you fall asleep and reaching its lowest point before rising again to help wake you up. A peer-reviewed overview of sleep and thermoregulation states plainly that core temperature "starts to decrease under circadian control" hours before sleep onset, continuing to fall through the night. Multiple independent summaries of the research converge on the same rough window: the temperature nadir lands around 4–5 AM for someone with a typical sleep schedule.

10–11 PM Core temperature already declining, helping trigger sleep onset
~4–5 AM Temperature nadir — the body's lowest point
Pre-wake Cortisol rises, temperature climbs, preparing you to wake

Why "two hours before wake" is the more useful way to think about it

4–5 AM only means something if you actually wake around 6–7 AM. The pattern itself is anchored to your wake time, not a fixed clock hour — a patent filing on sleep-cycle detection describes the temperature minimum as occurring "about two hours before usual wake time" when circadian rhythm and sleep schedule are properly aligned. That's a more portable way to use this fact: whatever time you personally wake up, your body is already doing the least work to stay warm roughly two hours before that — no need to know anything about your city's climate to apply it.

Why this doesn't need local climate data: earlier versions of this guidance tried to also verify each city's coldest ambient hour, which meant building and maintaining city-specific data. Anchoring to wake time instead means the recommendation works the same way everywhere, because it's based on something your body does regardless of where you live.

What to actually do with this

The practical version: an hour of reduced cooling — Dry Mode, or fully off — ending right around your usual wake time asks the least of your body at exactly the point it's already asking the least of itself. See our Dry Mode article for how much that saves, and try the calculator below to see the combined effect for your own sleep schedule.

Try it with your own wake time →
Try the calculator — no sign-up, results in seconds

Sources

  1. "Sleep and Circadian Rhythmicity as Entangled Processes Serving Homeostasis" — ScienceDirect — core temperature begins declining under circadian control approximately two hours before sleep onset, continuing through the night.
  2. U.S. patent filing on sleep-cycle/circadian phase detection — describes the body temperature minimum occurring "about two hours before usual wake time" under normally-synchronized conditions (cited for the general pattern, not as a primary sleep-science source).
  3. Neurolaunch — "Does Your Body Temperature Drop When You Sleep?" — consumer-facing summary citing the ~4–5 AM nadir, consistent across multiple independent secondary sources.

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