Overview
- Condensation forms when warm, moist air cools below its dew point on cold surfaces, so cold window panes, exterior walls and cellar ceilings are prime spots for water to collect.
- Ventilate by stoßlüften—short, wide openings rather than tilt—using season‑adjusted times (roughly 10–20 minutes in spring/autumn and 3–5 minutes in winter) and avoid leaving an unheated cellar open on warm autumn days because warm outside air can increase moisture.
- Measure, don’t guess: place a thermo‑hygrometer away from radiators and exterior walls to track room humidity, watch for sustained readings above about 70% as a clear warning sign, and use an infrared or surface thermometer to compare wall temperatures with the dew point.
- Use the practical 20‑50 orientation—around 20 °C and 50% relative humidity—with living rooms near 19–21 °C and other rooms kept above about 16 °C to reduce surface cooling that causes condensation.
- Treat dehumidifiers as a targeted backup when heating and ventilation fail; compressor units typically draw about 200–300 W and can cost roughly €13–€20 per month at moderate use, but they do not fix cold walls or seepage so persistent problems require insulation or structural repair.