The windows inside your home have an enormous impact on the overall energy efficiency of your home. They’re so important that their efficiency level and placement are a large part sizing HVAC systems for homes. Recent improvements in window engineering have increased their ability to resist temperature change and air leakage to the point where a window can now carry the Energy Star label.
Efficiency Ratings
- U-factor — This number ranges from .20 to 1.20 and describes how well the window retains heat indoors during the heating season.
- Visible transmittance (VT) — VT refers to the amount of light that the glass allows through it. The scale runs from 0 to 1, and higher numbers indicate more light transference.
- Solar heat gain coefficient (SHGC) — This term refers to the amount of heat the glass transfers from direct sunlight. If you want to take advantage of passive solar heating during the cooler months, choose a window with a high SHGC. However, if that window receives strong sunlight in the summer, it will also increase the heat gain.
- Air leakage (AL) — Not all window manufacturers disclose the window’s AL rating. AL ratings run from 0.1 to 0.3, and lower numbers indicate less leakage.
Frame Materials
Wood, aluminum, vinyl and fiberglass window types are available, and of them, fiberglass frames offer the lowest maintenance and highest energy efficiency. Wood and vinyl products react to temperature changes. Wood is susceptible to shrinkage and swelling from varying levels of humidity. Aluminum frames conduct heat rapidly, which makes them the least energy efficient of all window types.
Glazing
Components of a window that receives the Energy Star label include low-E (low emissivity) glass mounted as dual or triple panes with a gas fill. Low-E glass blocks much of the heat transfer in and out of the window. Since glass itself has almost no ability to resist heat transfer, choosing low-E windows reduces conditioning bills year-round.
Looking for windows that earn high efficiency ratings or carry the Energy Star label will cut your cooling bills. To learn more, contact Ace Hardware Home Services, providing HVAC services for Dayton-area homeowners.
Our goal is to help educate our customers in Dayton, Ohio about energy and home comfort issues (specific to HVAC systems).
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