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When looking to replace your windows, remember these important criteria when selecting true energy-efficient windows. When done properly your windows will significantly reduce heating and cooling loads while still allowing natural light into the home.

1. Insulating capability – this is how well the window performs at keeping heat inside the home in the winter season and keeping the heat outside the home during the summer season. This is also known as the U-value of the window. The lower the U-value, the better the window is at reducing heat transfer through the window.

2. Solar heat gain – refers to the increase in temperature in a space, object, or structure that results from solar radiation. A window with high solar heat gain can reduce heating loads in the winter, but may overheat the home during the summer. The amount of solar gain increases with the strength of the sun, so selecting a window to work with the coordinates of the sun can moderate solar heat gain. The solar heat gain coefficient is SHGC.

3. Natural day lighting – is the amount of visible light that is allowed to pass through a window. This is referred to as visible transmittance (VT). More light is generally better, but comes with a compromise of insulating capability and solar heat gain criteria.