We Can help
Lake Washington Windows and Doors prides itself on making the window shopping experience as painless as possible. We are here to help you every step of the way as you buy new windows! However, we know that customers also want to feel comfortable and confident in their purchase, so we’ve outlined a few helpful terms you should know when you’re shopping for your new windows.
Ratings to Look for When you Buy New Windows
- Air Infiltration Rating: This rating will give you a sense of how impermeable the window is to leaks from both the inside out and outside in. It’s determined by measuring how many cubic feet of air pass through a square foot of window under specific conditions. Just as if you’re playing golf, who want this number to be low as that shows better performance. Picture windows, casements, and awning style windows will have lower air infiltration rates then sliders and double-hungs.
- Structural Class Rating: This gives you an indication of the strength of the window. There are two main components to determining the strength of a window. First, the structural class. The two most common structural classes are C=commercial and R=residential. Second, the rating itself, measured in terms of lbs. per sq. ft. Often referred to as DP rating (DP=design pressure), a “40” rating for example means a window has passed a test of 40 lbs. per sq. ft. of pressure. This is equivalent to a wind pressure in excess of 100 mph. The higher the DP rating the stronger the window. Ideally, you want a window with a “C” or commercial structural class and one that has a higher rating, 40 being extremely strong (C40).
- Energy Star Rating: These ratings are administered by the U.S. Department of Energy’s Energy Star program. Qualification criteria will vary based on the climate zone and is based on a product’s performance in National Fenestration Rating Council testing. We are in the Northern Territory which calls for a U-Factor of ≤ 0.30 and Solar Heat Gain Coefficient (SHGC) of ≤ 0.35.
- National Fenestration Ratings Council: Tied with the Energy Star Rating, the NFRC is a nonprofit organization that offers standardized ratings of windows. While not mandatory, most window manufacturers opt to have their products rated.
- R-value: This measures the substance’s resistance to the flow of heat. For windows, it’s best to have a low U-value and a high R-value since they’re the inverse of each other.
- U-factor/U-value: This measures a windows thermal conductivity or the rate of flow of energy through a window frame, thus a lower U-value indicates better efficiency. U-value is the inverse of R-value. The higher the R-value the better its Resistance to thermal conductivity, and the lower the U-value the better because the rate of thermal flow through the window frame is lower.
- Visible Transmittance: This rating indicates how much light passes through the glass. The higher the number, the greater light transmission.
For more helpful terms as you buy new windows, check out HGTV’s glossary of terms. Have questions? Feel free to call (425) 255-2600 or email us and we’re happy to help.
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About Lake Washington Windows & Doors
Lake Washington Windows & Doors is a licensed general contractor specializing in replacement window products, replacement doors, and home siding replacement. Our service area extends throughout the Greater Seattle area, including Bellevue, Issaquah, Kent, Renton, Woodinville and more. The professional team at Lake Washington Windows has more than 100 combined years of window, door and siding experience, so you can rest assured that we can recommend the best solution for your home and budget. Contact us online to request an appointment or inquire about products and services.
