Energy Efficient Windows FAQs

If you’re in the market for energy efficient windows, then you’ve probably realized that there’s a bit more to it than a “bad-vs-good” window choice. There are labels, acronyms, ratings, gases, films, and all sorts of things that can get a little overwhelming.

We’ve put together a collection of questions we’re regularly asked, as well as some information we think is important to help your window purchase decision.

Have a question that we didn’t address? Ask in the comments below, or contact one of our window experts at (855) 415-6637.

What does Low-E mean?

Low-E stands for low-emittance, and refers to an invisible metal or metallic oxide coating on glass that diminishes heat transfer by reflecting heat while allowing light to pass through. It also helps reduce transmittance of UV light, protecting fabric, carpet, and furniture from fading.

What is Argon?

Argon is a natural, colorless, non-toxic gas that is denser than air and adds layers of insulation between two or three panes of glass to further reduce transfer of heat or cold.

What is a U-Factor?

A u-factor is a measurement of heat that passes through window glass. The lower the u-factor, the more energy efficient the windows. The range is typically between 0.25 and 1.25.

What is Solar Heat Gain Coefficient (SHGC)?

The SHGC measures the fraction of solar energy transmitted, representing how well the window blocks heat caused by sunlight. The range is typically between 0.25 and 0.80, and the lower the SHGC, the less solar heat is transmitted.

What is Visible Transmittance (VT)?

VT measures the amount of light the window lets through. Generally measuring on a range between 0.20-0.80, the higher the VT, the more light will be allowed through the window.

What is Air Leakage (AL)?

This one is pretty self-explanatory. Air leakage is the rate at which air passes through the joints in the window. It is measured in cubic feet passing through at one square foot of the window area per minute. The lower the AL value, the less air leakage. The industry standard requires no more than 0.3 cf m/ft^2

Can replacing windows really save me money?

It depends. There are a few factors that will determine whether or not you save money in the long run, the largest factor of which is the current state of your windows. Replacing all the windows in your home¬† with energy efficient windows will cost on average $7500-10,000. Over 70% of this is recuperated in added home value, and can produce between $111 – $465 annual savings on energy bills. This means, typically, you’ll save/recuperate $5.1k-7.2k in the first year. After that, the energy savings will, on average, recuperate your costs for a new windows between 6-10 years. So if you already have well-structured, well-maintained windows, then it would not make sense to replace them, because the efficiency gain would not be great enough to make a difference. Similarly, if you’re not planning on staying in a home longer-term, then the investment may not be worthwhile except to add home value. Read more about this topic in our infographic.

What is Energy Star?

Energy Star is a United States Environmental Protection Agency (EPA) that works toward the adoption of energy efficient products, practices, and services through partnerships, objective measurement tools, and consumer education. Any Energy Star products are third-party certified based on testing in EPA-recognized laboratories, and off-the-shelf verification testing each year.

What is NFRC?

Energy Efficient Windows NFRC labelNFRC is the National Fenestration Rating Council, and is a third-party non-profit organization that sponsors certified rating and labeling to better help consumers compare efficiency of products such as windows, doors, and skylights. NFRC windows typically look like the image to the right and represent the ratings discussed in the FAQs above.

What is the map on the label for?

The map on the Energy Star/NFRC label shows the different climate zones in the U.S. Each climate zone has different specifications to be Energy Star rated. There are 4 climate zones:  Northern, North-Central, South-Central, and Southern. Energy efficient windows, doors, and skylights can be Energy Star rated for more than one climate zone.
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One thought on “Energy Efficient Windows FAQs”

  1. For hot climates, low-E coating should be applied to the outside pane of glass. If the windows are designed to provide heat energy in the winter and keep heat inside the house typical of cold climates, the Low-E coating will maximize benefit by being on the inside pane of glass.

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