How Different Operating Windows Ventilate

photo of an empty room with replacement windowsOperating windows are natural ventilators. When strategically placed where prevailing winds pass through, they can push moisture-ridden air out, and rid your home of pollutants and regulate your indoor climate.

But then again, all windows are not the same; some are more efficient than others. To plan your window replacement project in Salt Lake City, you must first understand how different units ventilate. Here is a primer:


The casement utilizes nearly 100% of the opening for natural ventilation. Unlike other operating windows, it consists a single glass panel that cranks outward. When opened completely, it provides top-to-bottom ventilation.

If you install at least one casement window on both sides of the room, you can optimize cross ventilation. In turn, you maximize up to 65% of outside air velocity.

Further, the casement allows you to control ventilation. Since the wind rarely flows directly to windows, you could angle the single panel of the casement to capture breezes effectively.

Double Hung

While casements perform best with cross ventilation, double-hung windows make the most of the stack effect. This phenomenon is when warm air rises, leaving some room below to be filled by cold, dense air.

If you leave both sashes of double-hung units ajar concurrently, the rising air exits through the upper panel, while cooler air enters through the bottom.

In other words, you could make your indoor space cooler even in the absence of external winds. The closer the windows are to the ceiling, the more effective the stack ventilation would be.


Bay windows comprise at least two casement or double-hung units. They can breathe in fresh drafts in more than one direction, heightening the ventilating qualities of the windows mentioned above.

Natural ventilation is only one of the factors you need to consider when choosing replacement windows. Think about the unique needs of your home, and reconcile form and function to pick the right style for each of your rooms.