Photo from Department of Energy.
I bet you just got used to hearing about double pane, Low-E glass, Argon filled windows. You know the ones. The ones labeled as ENERGY STAR? Now, there is a new babe in town getting a lot of attention from the Department of Energy. The R-5 window has all the right curves and significant energy savings compared to its distant cousin, the ENERGY STAR window. Yep, this R-5 is energy efficient beauty with triple panes of either high solar-gain, Low-E Glass, Argon/Krpton Gas or high solar-gain, Low-E Glass, Argon/Krpton Gas, depending on your area of the country. According to the DOE,
“Common ENERGY STAR windows only have an R-value of 3. Increasing the R-value from 3 to 5 reduces average heat loss through the windows by 40% and saves consumer money on energy bills.”
But why are the R-5 windows the darlings of the DOE?
“Windows in the U.S. account for 30% loss of building heating and cooling energy, representing an annual impact of 4.1 quadrillion Btu (quads) of primary energy. Windows have an even larger impact on peak energy demand and on occupant comfort.”
So are these babes for everyone? They are best suited for cold and mixed climate areas. So, why isn’t everyone jumping on the R-5 bandwagon? Cost versus energy efficiency. That energy type rope. (Isn’t that always the problem?)
Well, never fear; the DOE is working on developing a volume purchase program so that they are affordable. How affordable? A price premium of $4/ft² compared to today’s typical ENERGY STAR windows. For more information about marginal costs versus savings for highly insulated windows in different climates, see here.
At present, the agency has just released its newest draft specifications for the windows and awaiting comments. (The U-factor for fixed windows: less than or equal to .20 and operable windows with a U-factor of less than or equal to .22. Note, U-factor is the measurement of heat loss through a window.) The comment period ends November 13, 2009. The Agency anticipates affordable windows will be available July, 2010.
What make the R-5 windows so special? According to the Efficient Window Collaborative,
“Triple-Glazed** with High-Solar-Gain Low-E Glass, Argon/Krypton Gas
This figure illustrates the performance of a window with a very low heat loss rate (low U-factor). In this case there are three glazing layers and two Low-E coatings, 1/2″ argon gas or 1/4″ krypton gas fill between glazings, and low-conductance edge spacers. The middle glazing layer can be glass or plastic film. Some windows use four glazing layers (two glass layers and two suspended plastic films). With this window, both Low-E coatings are spectrally selective in order to minimize solar heat gain. This window is best suited for climates with both significant heating and cooling loads.
Triple-Glazed** with Low-Solar-Gain Low-E* Glass, Argon/Krypton Gas
This figure illustrates the performance of a window with a very low heat loss rate (low U-factor). In this case there are three glazing layers and two Low-E coatings, 1/2″ argon gas or 1/4″ krypton gas fill between glazings, and low-conductance edge spacers. The middle glazing layer can be glass or plastic film. Some windows use four glazing layers (two glass layers and two suspended plastic films). Both Low-E coatings in this product have high visible light transmittance. The use of three layers, however, reduces the beneficial solar heat gain. This product is suited for buildings located in very cold climates, although Double-Glazed with High Solar Gain Low-E should be considered if passive solar heat gain is desired.”
For more detailed information about different glazing area of windows, see here.
If you are like me, you probably still have questions. The Alliance to Save Energy hosted a webinar for its members or interested parties about window energy efficiency. Information about R-5 windows was presented. In addition, underneath the webinar video is a list of questions that were asked regarding window films, vacuum-filled glazing, triple glazing/R-5 windows, and other topics. I found the questions and answers fascinating and provided me with a more in depth understanding of window energy efficiency.
So, readers, what are your thought about the new IT kid on the block, the R-5 window? Is its premium cost worth the energy savings? Let me know your thoughts.
{ 15 comments… read them below or add one }
great post!
That’s great, first time I hear of those. I have LOTS of glass surfaces in my house, I think I’ll do the math to see if it’s worthwhile. In my case, it’s double glass already, I might not replace it immediately. But last year, one window was broken (6ftx6ft) and I’d definitely replace that with these new ones if it happens again.
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never heard of those, sounds interesting!!
I heard about these windows a couple of years ago and got positively giddy about the energy efficiency. The fact that the price is significantly higher and that I have double paned windows that are energy efficient made me remind myself that the greenest thing is what you already own. But if I was in a situation where I had to replace old inefficient windows in my house, I’d give them a good hard look. I admit it’s strange to be giddy about windows and building supplies but I am.
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I believe that eventually this will be the norm of all mid-level to high-end home and office construction. Although the cost is much higher per unit, but over time the energy savings will more than pay for the windows themselves. I assist my customers day in and day out with their cypress lumber needs as well as other specialty wood and I can tell you that almost all of them want to save money in their future energy costs. You have to figure that a house is an investment and you need to prepare for the future by choosing these windows as the price of everything is rising, so will the cost of electricity. Think of this as buying a hybrid vehicle versus a gas guzzlers, you will expect to pay more up front but it will pay off over time.
David Williams
I seem to recall that triple pane windows were all rage, at least in the colder climates (Denver) back in the 80’s. Then they fell out of favor.
In fact, when starting the passive solar straw bale house that we just completed, I asked about them and was told common wisdom decided they weren’t necessary. As I was VERY busy with all the other details, I never followed it up.
But the bottom line is, I don’t think this is a new concept.
Kosh, you are probably right. I think the new concept is that the Government is trying to negotiate a lower price for the windows so more people will use them. Anna
Tell us more about your straw bale house? Have any pictures?
The volume purchasing program will help increase demand for these energy saving R-5 windows, just like the renewable energy tax incentives have increased the installation of residential photovoltaic solar electric systems. If it pencils out financially, people will eventually want them.
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The main reason why one would not switch from double pane to triple pane even though triple pane can be much more energy efficient, is the cost factor. Triple panes cost considerably more than double. But if the price is now going to come down, then it would make it easier for folks to decide to go with triple panes, I think.
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A SPECIAL THANKS TOO:
I would like to extend a Special Thanks to all the brave owners of retail window companies across America that have had the courage to sell and install these highly energy efficient windows for more then two decades. These men and women have paved the way in a direction America should have always been on and now that we as a country with the support of the Department of Energy should never be forgotten as more new retail companies begin selling R-5 or better windows. Along with the also brave and confident manufacturer’s that spent their money on the expensive machinery with the hopes that through hard work, outstanding marketing, new technologies, excellent installation this adventure would prevail, and it has. We like to say these retail window companies were “Green long before it was popular”. Marc LaFrance with the DOE is also owed a special thanks for spearheading this R-5 Volume Window Program which with good public awareness campaigns will change the window landscape forever and for better. The day of the cheap hollow vinyl double glass window is over.
Window manufacturers can really effect the environment in a positive way with this technology. All new houses can be built with very economically friendly windows thus saving energy.
Just keep in mind that R-value is not linear (i.e. going from R-1 to R2 will halve the heat transfer, but going from R-2 to R-3 does not). U-Factor is the rating we should pay attention to. U-Factor is the inverse of R-Factor. Lower is better. R-Value of 2 = 1/2, or a u-factor of 0.50; R-value of 3 = u-factor of 0.33. Even more imporant is that u-factor is the about of BTUs per hour per square foot per degree (F) that will pass through the window.
We just upgraded 10 windows in our home. That is 127.5 sq ft of windows. They were single-pane aluminum, which has a u-factor of ~ 1.15. The new dual-pane, low-e, argon filled windows have a u-factor of 0.27. When we have our heat set to 72 degrees and it’s 32 degrees outside, heat gains/losses from the insulation value of the windows went from 6,762 BTU/hr to 1,764 BTU/hr. this is with a u-factor of 0.27 (R-value of 3.7). That was a decrease of 4,998!
If we were to instead go with a R-value of 5 (u-factor of 0.20), the heat loss would decrease to 1,176 BTU/hr – for an incremental gain of 588 BTU/hr. Not a bad change, but not earth shattering either.
I guess what I’m saying is that financially, if people have dual pane windows, they probably won’t be able to justify upgrading them to triple if its purely a financial decision. But if a person has single pane, this does increase the encouragement of them to replace those old windows. We still have 9 more windows to replace (saving money for them). It will be interesting to see what happens!
Lh, thanks so much for a wonderful explanation. Is there a basic formula that anyone can use their u factor to find out the btu loss or gain? Anna
Calculation for BTU/hr loss or gain:
(U-Factor) x (Sq Ft of window) x (Outside temp – inside temp [in degrees F]) = BTU/hr
Example 1: Heat Loss in winter through a 10 sq ft window
(0.30) x (10) x (30 degrees outside – 72 degrees inside) = BTU/hr
0.30 x 10 x -42 = -126 BTU/hr (since it’s negative, you’re losing heat to the outside)
Example 2: Heat Gain in summer through a 10 sq ft window
(0.30) x (10) x (100 degrees outside – 75 degrees inside) = BTU/hr
0.30 x 10 x 25 = 75 BTU/hr (positive number, therefore house is gaining heat)
As you can see, if an old single pane window with aluminum frames has a U-Factor of 1.15, it will have almost four times the heat gain or loss.
Summary: Old windows bad, new windows good.
lh newbie, is there a site that generically tells you what your windows’ u factor could be if you don’t know? How does the type of framing around the window get taken into account? Or does it matter for your BTU formula?
Also, is there a formula to use that tells you what you would be saving per year if you do change your windows? Anna