Having energy efficient windows and doors can greatly impact the energy use of your home. With a typical home, this can translate to several hundred dollars of savings each year. When evaluating potential options, there are several characteristics to look for, all centering around the three main functions of heat gain/loss, sun transmittance and personal style.
The NFRC Rating
The National Fenestration Rating Council (NFRC) is a voluntary program that tests, certifies, and labels windows and doors on their energy efficiency. Using their rating system is a reliable and simply way to compare products. Having energy efficient windows and doors that allow heat to enter and keep it from leaving is vital to maximizing your home’s energy efficiency. In this regard there are five things to look for.
Window Qualities to Look Out For
This is the rate at which a window or door conducts non-solar heat flow. It’s possible the U-factor rating just refers to the glass or glazing, however, NFRC U-factor ratings take into consideration the entire window or door. The lower the U-Factor rating a window or door has, the more energy efficient it is.
- Solar heat gain coefficient (SHGC)
SHGC is the fraction of solar radiation that passes through a window or door. It can be transmitted directly and/or released as heat inside a home. A lower SGHC means it lets less solar heat through and that your window or door has better shading capabilities.
- Air leakage (AL)
You might think air leakage is measuring how much air escapes a house, but it’s actually the opposite—how much outside air gets in. The lower the air leakage, the less air a product lets in. Not every product has air leakage ratings.
- Visible Transmittance (VT)
How much light passes through a product is measured by Visible Transmittance. A higher VT means more sunlight is passing through. You’ll want a VT that fits with your home’s daylight requirements.
- Light-to-solar gain (LSG)
It’s the ratio between the VT to the SHGC. A higher LSG ratio means more light and less heat passes through. LSG is another measurement that may or may not be provided.
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