Natural Ventilation: The “Chimney Effect”

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

Moving air ventilates your home by entering or leaving windows, depending on their orientation to the wind. When wind blows against your home, air is forced into your windows. accumulates in your home during the day, and the cool night air can flush it out.

For drier climates, this will mean ventilating at night, and closing doors, windows, and window coverings during the day. This may not apply in humid climates. Depending on the house 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 vacuum that pulls air out of the windows. The chimney effect occurs when cool air enters a home on the first floor or basement, absorbs heat in the room, rises, and exits through upstairs windows. This creates a partial vacuum, 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 home.

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 if you force the air to take a longer path between the inlet and outlet. Use smaller window openings for the inlets and larger openings for the outlets. This increases air speed and improves the cooling effect. Air from cooler, shaded outdoor areas provides the best intake air.

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

Solar heat travels in through the roof and radiates into the attic. Attic ventilation reduces attic 10 to 25 degrees and slows the of heat into the living space. However, the most effective way to reduce attic heat is to prevent it from entering in the first place with a reflective roof. Also very important is having at least a foot of attic insulation.