Sliding Window Energy Efficiency

October 11, 2010

Windows can account for a quarter of your heating and cooling costs. If you want to explore your options for windows with various degrees of energy efficiency, sliding windows are one such option. Sliding windows' energy efficiency can be increased by a number of factors.

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How Energy Efficiency Works

Energy efficiency rates three factors: solar heat gain, non-solar heat transmission (the "U factor"), and airflow. The non-solar heat loss happens by way of conduction, convection, and radiation through your window. Solar heat gains come from the sun shining into your home. Airflow happens intentionally when you open the window or unintentionally, which is called infiltration or leakage.

A sliding window is one type of sash style. The materials your window is made from and the sash style affect the above three factors. Generally, wood, vinyl, or fiberglass frames are better insulators than aluminum or other metals, so choose sliding windows in these materials. The number of panes of glass, what fills the space between them, and the coating on the glass all affect the energy efficiency so sliding windows with a lower U factor will be more energy efficient.

Horizontal sliding windows usually provide minimal ventilation with an effective open area of 45 percent, which may make cooling a home naturally a bit less effective. Sliding windows can also be leaky, and leakage can be responsible for up to 10 percent of a home's energy usage. The lower the air leakage rating on the label, the better. Keep in mind that leakage ratings on windows don't account for installation, so maximize your sliding windows' energy efficiency with professional installation.

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