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Should windows be open or closed when using a dehumidifier?

Separate a controlled drying session from the ventilation a home needs throughout the day.

By Dehumidifier UK · Updated 6 October 2026 · Sources linked below

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Our answer

During a controlled dehumidifier session, usually close open external windows to limit continually replacing the air being dried. Continue necessary ventilation and extraction, and follow the appliance’s instructions. A dehumidifier removes water but does not supply fresh air or remove every indoor pollutant.

Why an open window changes the workload

The machine treats the air that passes through it. A constantly open external window can exchange that air with outdoors and change both temperature and moisture. Whether outdoor air helps drying depends on its temperature and water-vapour content; outdoor RH alone is not enough for the comparison.

A contained laundry session

Use an appropriate room, spread the rack and reduce unnecessary open-window exchange while the machine operates. Keep the airflow path open inside that room. Continue required ventilation and follow the model’s safe-placement rules. Do not cover trickle vents, block combustion-air openings or disable a fitted extraction system.

Whole-home humidity control

Internal doors may need to be open for useful circulation through several spaces, depending on the location and the manufacturer’s instructions. A single unit is not guaranteed to dry every room equally. Compare readings in the problem rooms rather than assume one hallway reading describes the whole home.

Bathrooms and kitchens still need extraction

Remove moisture near its source. Use the fitted extractor during and after activities as directed. A portable dehumidifier is not a substitute for defective ventilation and should not be installed in a wet location unless its exact instructions allow it.

Heating and ventilation are different from extraction

Heating can lower RH without removing the water vapour; the reading may rise again when the room cools. Ventilation replaces indoor air, while a dehumidifier condenses or captures water. For recurring damp, consider the whole building and investigate the cause rather than choosing one appliance setting as the remedy.

A routine to assess

  1. Measure room temperature and RH before the activity.
  2. Use source extraction and any appropriate appliance session.
  3. Check that humidity recovers and cold surfaces are not staying wet.
  4. If the same symptoms recur, document them and arrange investigation.

For positioning and rack setup, see where to put the machine and drying clothes indoors.

Sources and evidence

  1. GOV.UK: addressing damp and mould in homes
  2. Dartford Borough Council: damp, mould and condensation
  3. Energy Saving Trust: home appliances
  4. Meaco Arete Two 10L/12L official manual
  5. Meaco Arete Two 20L/25L official manual
  6. Electrical Safety First: dehumidifier safety

Sources checked 6 October 2026. Manufacturer specifications are claims under their stated conditions; they are not our household measurements.