What size dehumidifier do you need for your room?

A typical 12-15 m² bedroom with wet windows in the morning wants a 10-12 L/day unit — enough to reach 55% overnight and hold it. Check the noise spec if it runs while you sleep: under 35-38 dB on low speed is livable, and units with a humidistat shut off automatically at target.

It removes the condition mold needs: sustained humidity above 60%. Existing colonies must still be cleaned (spray, then repaint with anti-mold paint if the wall is marked), but with air held at 50-55% they don’t come back. If mold persists despite good humidity, the problem is different — a thermal bridge or water infiltration in the wall — and a dehumidifier only masks it.

A 20 L/day compressor unit draws 200-350 W while running — with the cycling behaviour of a correctly sized unit, count 1-2 kWh per day in the damp season, roughly €0.25-0.50/day. Desiccant models draw more (400-600 W) but work better in cold spaces like garages and cellars below 15 °C, where compressor units lose most of their capacity.

In the room with the problem, door closed — a dehumidifier "for the whole house" through open doors works poorly, air just doesn’t migrate fast enough. Keep 20-30 cm from walls for airflow, away from heat sources, and empty or hose-drain the tank regularly (continuous drain into a nearby sink or outlet is the upgrade nobody regrets). Run it hardest after showers, cooking and drying laundry indoors — the three big humidity injections of home life.