German Experts Advise Best Ventilation and Roller Blind Practices in Summer Heat

To keep indoor spaces cool during hot weather, experts recommend opening windows only in the early morning (before 8 a.m.) and late evening (after 9 p.m.) when outdoor temperatures are lower. Windows should be fully opened for short periods of cross‑ventilation rather than kept tilted or left open all day, which can pull in warm, humid air and raise the risk of mold.

For roller blinds, the advice is to keep them partially open instead of fully closed. Leaving a 5–10 cm gap at the bottom allows air circulation and prevents a heat‑stagnation pocket between the blind and the glass, which can cause the temperature to rise sharply and, in extreme cases, even crack the window pane. Using blinds together with shutters or curtains can further block direct sunlight while still permitting airflow.