When it comes to replacement windows ratings, there are a number of factors that can assist you in finding the best energy efficient windows for your home (and in your price range). However, it can a bit tricky though because the best windows for a hot climate won’t have the optimum ratings for a home in a cold, snowy climate. Nonetheless, understanding the main ratings can help you work with a knowledgeable contractor to find the best windows for your home.
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Replacement Windows Ratings
U-Value
Let’s start out with U-value. This is a measure of how efficiently (or poorly) a window prevents heat loss though the unit and ranges from 0.10 to 1.20. So, a lower U-value in a window means less heat loss occurs. As a rule of thumb, the best windows have a low U-value. Consumers should be looking for a window with a .30 U-factor or lower.
Window Cost Samples
American Craftsman 70: $400 installed
Gentek Signature Elite: $700 installed
Wincore 7700 Series: $700 installed
Okna 500 Series: $750 installed
UniShield Plus: $750 installed
ProVia Aspect Series: $800 installed
Andersen Fibrex Window: $1900 installed
Air Infiltration Ratings
AI or Air Infiltration is a measure of how much air passes through the window assembly (measured using the formula – cfm/sq ft). The is a number that range from 0 to 0.3. Therefore, a lower AI value means less air passes through the window and frame assembly. The lower the AI, the better and more energy efficient the window. AI, along with U-factor are the two most important window rating numbers that consumers should be looking at when comparing replacement windows and deciding on what to purchase. Consumers should be looking for a .08 AI or lower.
R-Value
R-value is the insulating value of a window assembly and is effectively the inverse of U-value. Window R-values range from 0.9 to 3.0. Therefore, the higher the R-value is, the better the insulating properties. As a rule of thumb, the best windows have a high R-value.
SHGC Ratings
Another replacement windows ratings is SHGC or Solar Heat Gain Coefficient. This is a measure of how efficiently the window blocks out solar heat from sunlight. The SHGC numbers range from 0 to 1, with 0 being no solar heat absorbed and transmitted through the window. Therefore, the lower the SHGC, the lower the amount of solar heat that comes through the window.
Visible Transmittance
VT or visible transmittance is a measure of how much sunlight enters through your window. VT is a number that ranges from 0 to 1. Therefore, a lower VT value means less light is entering through the window. A low VT means less fading of carpet and furniture over time.
Condensation Resistance Ratings
CR or condensation resistance is a measure of how well a window resists condensation forming on the inside surfaces. CR is a number that ranges from 0 to 100. A higher CR means better resistant to condensation forming. As a rule of thumb, the greater the CR value, the higer quality the window.
Sound Transmission Class
STC or Sound Transmission Class is a measure of how much sound a window blocks out. STC is a number that ranges from 18 to 50. So, the higher the STC, the more noise is blocked out by the window. STC is affected by the amount of dead space between window panes (the more space, the better), the quality of air seals and the thickness of the window glass. The higher the STC, the better the window is at keeping out outside noises.
Design Pressure Ratings
Our final replacement windows ratings is DP or design pressure rating. DP tests the structural load of a window by applying wind pressure on either side for 10 seconds. so, for instance, a DP30 rated window is tested up to 132 mph wind speed, while a DP40 rated window is tested up to 155 mph wind speed. A DP50 rated window is tested up to 173 mph wind speed. Incidentally, a DP50 rated window is the industry standard for “hurricane resistant.”
Related Topics
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Wincore Windows Reviews
