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Use night flushing and cross ventilation

Where nights are cool, you can flush the day's heat out of the building's thermal mass at night and keep the house closed through the hot day.

How

1. Open low windows on the windward side and high windows or vents on the leeward side at night so wind and the stack effect move air through.
2. Close windows and shading once outdoor air gets warmer than indoor air in the morning.
3. Where fans are used, add temperature and humidity sensors so only cool, dry air is brought in.
4. Do not rely on this in humid climates, where DOE notes natural ventilation can encourage mould, or when outdoor air quality is poor (smoke, dust).
5. Consider a whole-house fan in dry or moderate climates.

Safety: Secure ground-floor openings left open at night and keep wildfire smoke out (see safety module).

Sources

1. Natural Ventilation and Cooling. U.S. Department of Energy, Building Science Education, accessed 2026-11

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