Natural ventilation used to be the most common method of allowing fresh outdoor air to replace indoor air in a home. Today, it’s usually not the best ventilation strategy, especially for homes that are properly air sealed for energy efficiency. Natural ventilation also usually doesn’t provide adequate moisture control.

Natural ventilation occurs when there is uncontrolled air movement or infiltration through cracks and small holes in a home—the same ones you want to seal to make your home more energy efficient. Opening windows and doors also provides natural ventilation.