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Determining Energy Savings

Looking for Energy Saving Windows? It’s SIMPLE… Just check for the ENERGY STAR label


ENE_crt_cThe ENERGY STAR or NFRC label makes choosing high performance windows simple. We no longer need to be concerned with companies claiming their windows have this R-value, that air-infiltration, or boasting about other confusing and often misleading data. Now all windows must be tested under equal conditions, and the values shown on the NFRC label are certified under Federal Law. So to compare windows, simply have a look at the values on the label, and use the Guide below.

Current ENERGY STAR Performance Criteria
In response to changing technologies and international codes, beginning January 1, 2015 windows are now required to meet new, more difficult to achieve U and SHGC values to be labeled as ENERGY STAR. For most of Maryland, Virginia and Washington DC, windows are required to have a U-Value <= 0.30 and a Solar Heat Gain Coefficient (SHGC) <= 0.40.




U-ValueSometimes also called the U-factor, it is a measure of how well heat is transferred by the entire window — the frame, sash and glass — either into or out of the building. Like golf scores, the lower the U-value, the better the window will keep heat inside a home on a cold day. Typical U-values for windows range from 0.50 (poor) to 0.18 (excellent).


SHGCA window’s SHGC is a measure of it’s ability to transmit warmth caused by sunlight. A lower number means less of the sun’s heat is getting through, resulting in reduced air conditioning costs during the summer season. Typical SHGCs for windows range from 0.61 to 0.18. IMPORTANT NOTE: When comparing U and SHGC values, make sure they are from the NFRC product sticker, not “Glass” or “Center of Glass (COG)“ ratings. NFRC values are based on the “Whole Window” performance which more closely represent the energy efficiency of the entire window. To compare other values is to compare apples with oranges. Center of glass values are always lower (better) than whole window values.


NFRC StickerA window with the ENERGY STAR label must be tested by an independent laboratory, and certified by the National Fenestration Rating Council (NFRC). The NFRC label may also show other test results such as: Visible Transmittance— measures how much light gets through the window. A window with a high number will allow more natural daylight into your home. Values generally range from 0.20 to 0.80. Air Leakage— measures the rate at which air leaks through joints in the window. Values range from 0.00 (a completely sealed aircraft capable window) to 0.30— the maximum allowed by most building codes.


Weathermaster_Solar2In 1998, WeatherMaster became one of the first window companies to partner with the U.S. Department of Energy’s ENERGY STAR program. We know that the typical American home can easily be transformed into a highly efficient, more comfortable living space, that’s less expensive to operate. As we use less energy our air and water become cleaner, and energy independence will build a stronger United States. WeatherMaster is 100% committed to this mission-- we practice it in every facet of our business, from ultra high efficiency lighting in our warehouse, micro-zoned HVAC to heat and cool only occupied spaces, to our 20 kW solar array on our rooftop that produces 100% of the electric power we use.