Block sun and use cross-ventilation to flush heat out

Close blinds on sun-facing windows during the day and open windows on opposite sides at night to replace trapped heat with cooler air.

Why It Works

Up to 76% of sunlight hitting standard windows enters as heat. Blocking it on the south and west sides (Northern Hemisphere) during peak hours prevents heat from building up indoors. Opening windows on opposite sides once outdoor temps drop below indoor temps creates cross-ventilation, and placing a fan in an upper window pushes hot air out while cool air enters through lower openings (stack effect).

Steps

1. Close windows and draw blinds on south- and west-facing windows during the hottest hours.
2. Open windows on opposite sides of the house once outdoor temperature drops below indoor temperature, typically evening and early morning.
3. Place a box fan facing outward in an upper window to accelerate the stack effect.
4. Add exterior shading such as awnings or shade trees—these block heat before it reaches the glass, outperforming interior blinds.

Tips

• Reflective or blackout curtains outperform standard blinds for heat blocking
• Even cracking windows a few inches on opposite sides creates useful airflow