ventilation from double hung windows

One piece of advice you often hear from almost every window company is that one double-hung window is all you need to provide sufficient natural ventilation to a small to medium-sized room. But have you wondered if it works? 

Stack Ventilation

Double-hung windows are unique in that it’s the only window style that features two overlapping sashes. It can be opened so that you end up with two openings— one at the top, another at the bottom — when the sashes overlap. An average-sized double-hung window would have openings far apart enough to create airflow.

This type of ventilation operates on the principle of stack ventilation, which relies on the difference between indoor and outdoor temperatures. Since warm air tends to rise, the top half of an open double-hung window vents warm, stale air from the room. The pressure difference created by the vented air pulls cool, fresh air into the bottom half, resulting in proper airflow.

Benefits of Ventilation

This feature makes double-hung replacement windows ideal for small rooms and areas with only enough wall space to fit one window. Allowing ventilation for at least 15 minutes daily helps reduce indoor air pollutant levels. Indoor air pollutants are emitted by common household items such as paint, plastics, and aerosol products. Cooking and smoking likewise emit particles that can get trapped indoors.

Natural ventilation also helps regulate indoor humidity levels. Condensation on the windows indicates high indoor moisture levels, which can be flushed out with regular ventilation. It also helps prevent mold and mildew growth. If left to thrive, mold and mildew can trigger allergies and other respiratory problems. It can also cause unsightly black stains and unpleasant smells. While other window styles can provide ample ventilation, double-hung windows can do so with just one window, making it ideal for rooms of any size.

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