A Detailed Discussion of Triple Pane Windows & R-Values
Are Three Window Panes Better than Two When It’s Cold Here?
We’re often asked if three window panes will keep a home warmer than two during central Texas winters. On occasion, we also see window dealers trying to differentiate themselves by selling triple pane windows. So, we thought it would be helpful to write a post addressing the three vs two pane window cold weather debate. Intuitively, three panes does sound better than two. However, rather than looking at how many window panes, we recommend thinking first about the desired thermal performance for your region. Three pane windows are simply not needed everywhere. This is especially true for those with an R-Value rating of R-5 (although R-Values don’t necessarily apply to windows). Some companies market such windows in central Texas, but they’re generally only needed in very cold climates with long winters.
How are Triple Pane Windows Made?
Triple pane windows typically have double strength glass on either side with single strength in the center. This adds 25% more weight and explains why triple pane windows are bulkier. They need wide frames and beefy construction to support the heavy, extra glass. A triple pane glass unit also requires adequate support to avoid seal failures leading to fogging and leakage. Finally, glass replacement is expensive so look closely at warranties for these windows if you’re considering them.
Single, double, and triple pane window construction in that order
What are R-Values, U-Factors, & SHGC?
- U-Factor measures the rate of heat loss expressed as BTU/hr·ft2·°F. Having a lower U-Factor means a window provides superior insulation to better retain warmth. In addition, U-Factor calculations include convection, conductance, and radiation within and next to a window. They also directly predict heat transfer. (1),(4)
- SHGC is the fraction of incident solar radiation a window admits directly, as well as that which is absorbed by it and released inward. 3 SHGC measures the sun’s energy and the radiant heat coming from window glass. Lower SHGC energy efficient windows reduce incoming heat and A/C costs.
- R-Values rate heat flow resistance through building materials like insulation. The NFRC and EnergyStar.gov don’t recognize R-Value as a window rating for technical, consumer, and legal reasons. However, no guidelines restrict its use for fenestration products.
Why are R-Value Energy Efficiency Ratings not for Windows?
Some window companies market the insulation rating of triple pane windows using an R-Value of R-5. The fact is that rolled or blown insulation carries much higher ratings like R-38. Higher R-Values indicate better insulating effectiveness for building materials, but they’re not generally helpful with windows.
More About Why Triple Panes are Unecessary in Central Texas
Living here you’ll probably NEVER recoup the expense of triple pane windows. This is because they’re designed for extreme cold-weather climates with extended winters. Regions like ours with long, hot summers and mild winters are not well served by this technology. In fact, many triple pane R-5 window benchmarks use zero degrees as their performance standard. I’ve lived in Austin for 30 years and only recall a few dozen days with temps below 20. The truth is we just don’t get super cold weather like northern states do. Furthermore, in Texas the heat starts building in March and lasts through November. That’s why we’re in the southern zone on the Energy Star map – ours is primarily a hot climate! For this reason Ringer Windows are engineered to work best in central Texas. Finally, this is where we build and sell most of them!
Why High-Quality, Low-E Coated Glass Really Matters Here
Why is it important to have great-quality, triple-coated glass like LoE-366 in central Texas? Because the heart and soul of a good Texas window is the quality of its Low-E coating. This is what stops most of the sun’s energy from passing into your home when it’s hot. How well a window works during cooler months is also important and is expressed by its U-Factor. However, triple pane windows make less of a difference in winter than you might think. That’s because it doesn’t get cold enough here for an extra glass pane to make any real difference.
Click the Map for US Energy Star Performance Criteria for Texas
Triple Pane Windows Only Make Sense in Central Texas if:
1. They add minimal cost to the price of the windows.
2. They maintain a Solar Heat Gain Coefficient of at least .22 or lower.
3. You’re satisfied with a triple pane window sash 25% heavier than a double pane with double strength glass.
4. You’re satisfied with the bulkier look of triple pane windows. Their frame construction is thicker and heavier because it is designed for cold weather.
5. The cost of replacing triple pane glass is satisfactory to you.
We Offer Double Pane Window Glass with Triple Pane Performance
We’re pleased to offer glass for double pane low-e windows that can match triple pane winter energy efficiency! This product is called LoE-i89 and is supplied to us by our partner, Cardinal Industries. It features a spectrally smart LoE3-366 triple coating, argon gas fill, and an added permanent Indium outer layer (i89). The additional coating reflects heat back into your home providing a 2.0 U-Factor rating just like triple pane glass! Even more, LoE-i89 double pane windows eliminate unwanted triple pane weight. Lastly, they maintain an average SHGC of 0.22 for incredible summer energy efficiency! Lastly, our windows are designed to combat the hot Texas sun and with bigger glass for brighter views.
Call us today at 512-989-7000 to get quotes for all your window needs.
Greg Ringer, Owner
About the Author
Greg Ringer, owner of Ringer Windows, has been making energy efficient windows for central Texans since 2006. He knows the importance of energy cost savings and emphasizes a no-pressure approach to vinyl window sales. Greg shares his knowledge of window manufacturing, sales and replacement windows through his blog, “The Truth About Replacement Windows“.
