TRIPLE PANE WINDOWS: R-5 RATING
A Detailed Discussion of Triple Pane Windows & R-Values
by Greg Ringer & Georgia Torok, Ringer Windows
On occasion, we run into window dealers trying to differentiate themselves by selling triple pane windows. After all three panes are better than two, right? Intuitively it sounds better but the truth may surprise you! Deciding whether to use triple pane glass should be based on the desired thermal performance for your region. It is simply not needed everywhere. Some companies also market triple pane window R-Values at an R-5 rating. In general, these windows are only for very cold climates with long winters.
Triple Pane Window Construction
Triple pane windows typically have two double strength glass panes with one single strength in the center. This adds 25% more weight and explains why triple panes are bulkier. They need wide frames and beefy construction to support the extra glass. A triple pane glass unit requires adequate support to avoid seal failures leading to fogging and leakage. Glass replacement is expensive so look closely at warranties for these windows.
Energy Efficiency Ratings: R-Values are Only for Building Materials
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 not windows.
What are R-Values, U-Factors and SHGC?
- U-Factor measures the rate of heat loss expressed in BTU/hr·ft2·°F. Lower U-Factor windows retain warmth indicating superior insulation. The U-Factor calculation includes convection, conductance and radiation within and next to a window. U-Factors 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.1 However, no guidelines restrict its use for fenestration products.
The Truth About Triple Pane Windows in Central Texas
Living here you’ll probably NEVER recoup the expense of triple pane glass. This is because it is designed for extreme cold-weather climates with extended winters. Regions 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 times when the temperature dipped below 20 degrees. The plain, simple 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. 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 Texas where we build and sell most of them!
High-Quality Low-E Coated Glass Really Matters
The true test of how well a window works in Texas during cooler months is expressed by its U-Factor. So, why isn’t there much of a difference you might ask? IT DOESN’T GET COLD ENOUGH here for an extra glass pane to make any real difference. The heart & 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. That’s why it’s important to have great quality, triple-coated glass such as LoE-366 in Texas!
Click on the Map for US Energy Star Performance Criteria for Texas
Triple Pane Windows Only Make Sense in Central & South 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.
Ringer Windows Offers Double Pane Glass With Triple Pane Performance
We’re pleased to announce a new double pane low-e glass that matches triple pane winter energy efficiency! Cardinal LoE-i89 features spectrally smart LoE3-366 glass with argon gas fill and an added permanent Indium outer coating (i89). This additional layer reflects heat back into your home providing a 2.0 U-Factor rating just like triple pane glass! Even more, LoE-i89 double pane glass eliminates unwanted triple pane weight. Further, it maintains an average SHGC of 0.22 for incredible summer energy efficiency! 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.
References:
1. http://glassmagazine.blogspot.com/2010/05/why-nfrc-uses-u-factors-for-windows.html
2. http://www.efficientwindows.org/ufactor.php
3. http://www.efficientwindows.org/performance.php
Greg Ringer, Owner
About the Authors
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“.
