How an under-duvet bed fan actually works

The duvet microclimate

Under a duvet, the air against your skin quickly reaches close to body temperature and near-100% relative humidity. At that point sweat stops evaporating, and evaporation is the body's main cooling mechanism during sleep. You are effectively wrapped in your own exhaust.

An under-duvet fan slides gentle airflow into that gap and continuously replaces the saturated layer with drier room air. The room does not have to be cold; the air just has to move.

Why it feels cooler than the thermostat suggests

Convective plus evaporative cooling at the skin creates a perceived temperature drop of several degrees at the same ambient temperature. Practically, a 22°C bedroom with airflow under the covers often feels better than a 19°C bedroom without it.

It also works in reverse for couples: one person gets targeted airflow while the other keeps the room temperature they like. That single fact resolves more thermostat arguments than any other feature we ship.

The Aerwell design choices

Every design decision on the Aerwell bed fan comes from that one job: move a modest amount of air, extremely quietly, exactly where it is needed.

• Folding frame so it clips to the bed edge and disappears in the morning
• Brushless motor tuned for low-speed smoothness rather than peak CFM
• 8-12 hours of battery so it runs a full night with no cable across the floor
• Remote control so you adjust speed at 3am without sitting up
• Multiple speeds, including one deliberately slower than most fans offer

Running cost

A window air conditioner typically draws 500-1500 W. A DC bed fan on a sleeping speed draws single-digit watts. Over a summer of nightly use the difference is the price of the fan several times over — which is why targeted cooling keeps making sense even where AC is already installed.