Natural ventilation relies on the wind and the “chimney effect” to keep a building cool.

The wind will naturally ventilate your home or business by entering or leaving windows, depending on their orientation to the wind. When wind blows against your home, air is forced into your windows. Heat accumulates in your building during the day, and the cool night air can flush it out. For drier climates, this will mean ventilating at night, closing doors and windows, and using window coverings during the day. You can use this strategy as long as indoor humidity is not uncomfortably high.

Depending on the building design and wind direction, a windbreak-like a fence, hedge, or row of trees that blocks the wind-can force air either into or away from nearby windows. Wind moving along a wall creates a low-pressure zone that pulls air out of the windows.

The chimney effect occurs when cool air enters a building on the first floor or basement, absorbs heat in the room, rises, and exits through upstairs windows. This creates lower air pressure, which pulls more air in through lower-level windows.

Natural ventilation works best in climates with cool summers or cool nights and regular breezes.

Using Windows and Doors for Cross-Ventilation
You can create natural cross-ventilation by opening your windows and doors, and adjusting the size and location of the openings to ventilate different parts of the building.

Inlets and outlets located directly opposite each other cool only those areas in between, in the direct path of the airflow. You’ll cool more of your home or business if you force the air to take a longer path between the inlet and outlet.

Experiment with different patterns of window venting to move fresh outside air through all of the rooms in your home or business. This may involve leaving some windows closed if they interfere with air moving along a longer path.

Attic Ventilation
Solar heat travels in through the roof and radiates into the attic. Attic ventilation reduces attic temperature 10° to 25°F (5° to 14°C) and slows the transfer of heat into the living space. However, the most effective way to reduce attic heat is to block the heat from entering in the first place with a reflective roof and at least a foot of attic insulation.

The best way to ventilate an attic is with natural ventilation. You need about one square foot of opening for every one hundred square feet of ceiling area. The vents should be split equally between the rooftop and the soffits. A fan is another alternative, but requires electricity to operate.

© 2004 U.S. Department of Energy