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Energy efficient windows help homeowners lower energy costs, including the costs of lighting, cooling and heating the home. As outlined by the US Department of Energy, selecting the best energy efficient windows for your home depends on factors of the home design, the climate in which it is located, the type of windows being installed and factors of their placement, such as shading, orientation and glazing.
Because of this variation in criteria, the top energy efficient windows for homeowners under some circumstances may not be the same as the top energy efficient windows for homeowners in other circumstances.
With that in mind, whether you're building a new home and incorporating energy efficient windows into the original design or you're remodeling your existing home to be more energy efficient, the following is a breakdown of the five best types of energy efficient windows for homeowners in the most common climate areas and house designs. To find specific manufacturers, models, and pricing, the Efficient Windows Collaborative has a Window Selection Tool that is incredibly helpful for finding the right energy efficient windows for any specific conditions.
In reading these comparisons, you'll come across two terms utilized in evaluating the energy efficiency of windows:
- U-Factor: a measurement of a window's ability to keep heat from escaping
- Solar Heat Gain Coefficient (SHGC): a measurement of passive solar heat passing into a home through a window, which can be beneficial for heating purposes but detrimental for cooling purposes
While these are by no means the only measurements of a window's energy efficiency (others include Visible Light Transmittance, Air Leakage and Condensation Resistance) they are two of the most common, important and convenient for basic comparison.
Lastly before proceeding to the specifics on the top energy efficient windows themselves, an important note regarding energy performance ratings of energy efficient windows: ENERGY STAR®, the generally accepted gold standard of energy rating authorities, gives minimum energy performance ratings for energy efficient windows. However, while these are an excellent guideline and a helpful start in determining the energy efficiency of home windows, they are incomplete, and therefore insufficient, determinants of the actual energy performance characteristics you'll need from your energy efficient windows, as they take only climate into consideration but not home design elements, such as the types, size and placement of the windows selected.
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Northern Region Homes
In the Northern region, such as in Minneapolis, Minnesota, where heating is the primary energy consideration, windows should have a low U-Factor and a medium to high SHGC. Ideal would be a triple, low-solar-gain, low-E glass in a non-metal frame with a U-Factor between 0.21 and 0.25 and an SHBC of 0.25 or less. These provide the best annual energy cost-efficiency, winter comfort and condensation resistance as well as reasonable summer comfort. For lack of that, similarly rated and framed double glass would suffice.
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North / Central Region Homes
For homes in the North/Central region, such as in Washington, D.C., where heating is the most important energy requirement but cooling is also a consideration, the best energy efficient windows have a relatively low U-Factor (slightly higher than for Northern region homes, but not much) and a high SHGC. Here, where condensation resistance is not as critical but electric peak is more critical, the same rated triple, low-solar-gain, low-E glass in non-metal frames is recommended, although best would be if they were also thermally improved, such as via a high-performance frame design or glazing, low-conductance gas fill or warm-edge spacer technology. Double glass alternatives would not do as well here as in Northern regions.
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South / Central Region Homes
In the South/Central region, such as in Dallas, Texas, where home cooling is the primary energy consideration but heating is still a factor, the top energy efficient windows for homes have a U-Factor in the middle ranges and a relatively low SHGC. Here winter comfort isn't nearly as much of an issue as summer comfort and condensation resistance is hardly an issue at all. Electric peak, however, is crucial in this region, as important as annual energy cost. For such purposes, triple glass may be overkill. Double glass is perfectly acceptable here, as long as it has low-to-moderate solar gain and low-E. Look for U-Factors of between 0.31 and 0.40 (or 0.25-0.30 if thermally improved) with an SHGC of 0.25-0.40 (or 0.25 or less if thermally improved). Non-metal frames are still recommended in this region, although in certain conditions, metal frames are acceptable.
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Southern Region Homes
The top energy efficient windows for homes in the Southern region, such as in Miami, Florida or Honolulu, Hawaii, where cooling is the key energy criterion, have a high U-Factor and a low SHGC. Annual energy cost, electric peak and summer comfort are the key criteria here, while winter comfort and condensation resistance are negligible factors. Here double glass is recommended, still with low-to-moderate solar gain and low-E. These windows, however, can also be housed in a wider variety of frames, including metal and non-metal, as well as metal with a thermal break.
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Extreme Northern Homes
Certain climates in the Northernmost regions, such as in Anchorage, Alaska, have prescriptive energy requirements, namely to promote heating and protect from extreme cold. In these environments nothing greater than 0.30 U-Factor can be tolerated, while any SHGC is acceptable.
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EnergySavers.gov: Energy Performance Ratings for Windows, Doors & Skylights
EnergySavers.gov: EnergySavers.gov: Window Selection
National Fenestration Rating Council (NFRC): Questions About Buying New Energy Efficient Windows
American Councile for an Energy Efficient Economy (ACEEE): Replace Old Windows
New Living Room Windows; Jfraser on Flickr