TRIPLE PANE WINDOWS: R-5 RATING
A Detailed Discussion by Greg Ringer and Georgia Torok, Ringer Windows
We’ve run into a few window dealers trying to differentiate themselves by selling triple pane windows. After all, 3 panes of glass are better than 2, right? Intuitively, it just sounds better, but the truth may surprise you! To evaluate if triple pane glass is right for your home, we need to look at the geographical area where you live as well as the desired thermal performance for your region.
A couple of window companies are marketing their Triple Pane Windows with an R-5 Value. In general, R-5/triple pane windows are designed to work best in extremely cold climates with long winter seasons.
TRIPLE PANE WINDOWS CONSTRUCTION
Triple pane windows typically have two panes of double strength glass and a single pane of single strength glass in the center. This adds more weight to the window (by 25%). Triple pane windows are bulkier construction to be able to accommodate the additional weight of the triple pane glass glazed unit. These windows need to have wider frames and beefy construction to support the weight of the glass. The triple pane glass unit must be adequately supported so as not to cause the glass unit seal failures causing fogging and leaking glass units. It is important to look at warranties on these windows. Glass replacement costs for triple pane windows are very expensive.
ENERGY EFFICIENCY RATINGS FOR BUILDING MATERIALS
Some window companies are marketing the insulating rating of this class of windows of their triple glaze windows as R-5 R-Value. Our homes rolled or blown insulation carry much higher ratings like R-19 or R-38. A higher R-Value indicates a better insulating effectiveness of specific building materials, (not windows).
WHAT ARE R-VALUES, U-FACTORS, AND SHGC?
U-Factor measures the rate of heat loss, expressed in BTU/hr·ft2·°F. The lower the U-Factor, the greater a window’s resistance to heat loss which indicates better insulating properties. U-Factor includes in its calculation the convection, conductance, and radiation elements that occur within and next to the window. This calculation directly predicts heat transfer. (1),(4)
• SHGC is the fraction of incident solar radiation admitted through a window, both directly transmitted and absorbed and subsequently released inward.3 SHGC is a measure of the total energy from the sun passing through a window, through direct transmission from the sun as well as radiant heat that warms the window and passes through to the inside. In hot climates, where a/c bills are a concern, energy efficient windows with a lower SHGC number will reduce the amount of heat coming through the windows.
Building Material Energy Efficiency Rating Term
• R-Value is the rating of the resistance of heat flow through specified building materials. NFRC and EnergyStar.gov don’t recognize R-Value as a window rating because of technical, consumer, and legal reasons.1 There are no direct guidelines regarding the use of R-values for fenestration products. R-Value indicates how well specified building materials keep the heat inside the home. Typically, R-Values rate the insulating value in specific building materials such as insulation but not for windows.
THE TRUTH ABOUT TRIPLE PANE WINDOWS IN CENTRAL TEXAS
The truth about triple pane windows/R-5 windows is simple if you live in Central or South Texas. You’ll probably NEVER recoup the extra expense of triple pane glass because it was specifically designed and intended for extreme cold-weather climates with extended winter periods. Climates with primarily long and hot summers are NOT well-served with triple pane windows and triple pane glass technology.
As a matter of fact, many of the benchmarks that pertain to triple pane/R-5 window technology use Zero Degrees as the benchmark for how well a particular window works. I’ve lived in Austin for 30 years and I can only recall a couple dozen times when the temperature dipped below 20 degrees. The plain and simple truth is, we just don’t get super cold like our neighboring northern states. Furthermore, Texas starts to get hot in March and it lasts through November. Texas is in the Southern Zone on the Energy Star Map. We live in a primarily HOT climate! At Ringer Windows, we designed windows to work best, right here in Texas where we build and sell most of them!
A true test of how well a window works here in Texas during our cooler months is expressed with the U-Factor. So, why isn’t there much of a difference you might ask? IT DOESN’T GET COLD ENOUGH here in Central Texas for an extra pane of glass to make any real difference.
The heart & soul of a good window in Texas is the quality of the Low-E coating. Low-E is what stops the bulk of the sun’s energy from passing through the glass into your home. It’s important to have a great quality triple coat Low-E glass, such as LoE-366 in Central and South Texas!
Click on the Map for US Energy Star Performance Criteria for Texas
TRIPLE PANE WINDOWS ONLY MAKES SENSE IN CENTRAL AND SOUTH TEXAS IF:
1. It adds minimal cost to the price of the window
2. The window maintains a Solar Heat Gain Coefficient of at least .22 or lower
3. You are satisfied with a triple pane window sash that will be 25% heavier than a double pane window with double strength glass.
4. You are satisfied with the bulkier look of triple pane windows. The frame construction of triple pane windows glass are thicker, heavier, and bulkier windows, designed for cold weather climates.
5. the cost of replacement triple pane glass is satisfactory to you.
RINGER WINDOWS RECOMMENDS DOUBLE PANE WINDOWS WITH TRIPLE PANE WINDOWS PERFORMANCE
Ringer Windows is pleased to announce a new double pane low-e glass option to match the winter energy efficiency of triple pane glass! Cardinal LoE-i89 is a double pane glass featuring the outstanding spectrally smart double pane LoE3-366 glass, with argon gas fill, with an additional outer permanent Indium coating (i89). This coating reflects heat back into your home to provide a U-Factor rating of 0.20 to match the U-Factor of the triple pane glass! The LoE-i89 double pane glass doesn’t add the unwanted additional weight of triple pane glass AND maintains an average SHGC of 0.22 for incredible summer energy efficiency! Here at Ringer, our double pane windows are designed with bigger glass that provides brighter views, designed specifically to combat the hot Texas sun.
Call today for window 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 efficiency for Central Texas homeowners 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“.
