Andersen’s Standard Low-E vs. Low-E Smart Sun with Heatlock
Zone 6 Andersen 100 Window Glaze :
We are building a version of the PGH in Zone 6.
Due to material shortages, we weren’t able to spec triple pane windows with our contractor, so settled on Andersen 100s.
We ordered the Low-E Smart Sun with/Heatlock glazing to get the .23 U-Factor.
Our contractor installed the regular Low-E glazing (without smartsun or heatlock) leaving most of our windows with a .27-.28 U-Factor.
It appears the benefit of the standard Low-E with argon is that it has higher visible light transmittance and higher solar heat gain at the cost of a poorer u-factor and lacking the heatlock coating.
How concerned should I be with the difference (ie should I settle for a credit for the mistake, or ask them to reglaze them all) from an energy efficiency perspective?
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Replies
Jim,
The energy hit is approximately 25%. 0.23 x 25% = 0.0575 ( + 0.23 = 0.2875) Without knowing the total glazing area and your local HDD level it is hard to judge the actual energy cost you will be experiencing over time. Given that you will hopefully see a 15-20 year life span for the windows it can add up. Since you did not receive the sunguard and heatlok features, you will also be experiencing the extra heat load of summer sun whcih will affect your AC energy costs.
Determining your energy losses can be a slippery an endeavor. If your particular site is subject to very long, but not very cold winters then the "extra" daylight gains could be argued to hold some benefit. I would find that a weak arguement for keeping the windows as total winter daylight hours will not offer much useful gain. North glazing is always a negative, east and west very limited gains compared to south glazings. Potential excess solar gain would be a similar pattern with modifying factors of trees, overhangs, orientation, etc.
The dollar cost to you of course will be determined by your gas or electric costs, which can (will) vary over the next 15-20 years. The fact that you say are building a version of PGH infers that the wall/roof areas of the house are better than code levels. The higher your wall/roof values the more the window area dominates your energy costs. Window/door losses can easily be a third of the total. Poor windows or lots of glazing can push that to half. You may have noted a common thread on GBA that improving windows is a much better bet than over insulating walls and roofs in cold climate buildings. Even the best window is still a pretty poor wall.
The choice you make will also be a comfort issue. Sitting next to a large glazed area on a winter evening will redefine the meaning of "Netflix and chill". If the contract calls for sunguard and heatlok then my vote would be insist on new sash for the frames. Or a completely free window package to cover future energy costs.
Andersen SmartSun is Cardinal's LoE³-366, while what Andersen calls LowE4 (or what you referred to a "regular LowE) is Cardinal's LoE²-272. Heat-Lock is Cardinal's i89 coating applied to glass surface 4, or the part of the window that you can touch inside your home.
The U factor difference between 366 and 272 (without i89 on either), is .01, so not significant, but 366 does a much better job of keeping solar heat out of your home....summer or winter.
Since you live in zone 6, heating tends to be a bigger issue than cooling most of the year and 272 will allow more solar heat through the glass, winter or summer. In the winter this is a plus, but not so much in summer.
While adding i89 to the glass package is not a factor in SHGC performance, adding i89 improves U factor by reflecting radiant heat back into the room, kind of like a mirror to infrared light. The potential downside to using i89 is that reflecting IR heat back into the room results in colder glass and an increased potential for glass condensation when it's really cold outside. And while the glass will be colder when using i89, it will still be warmer than it would be if both lites were clear, uncoated glass.
If I was buying windows for zone 6 application (disclaimer: I also live in zone 6 and I have triples), I would really want triples, but if that isn't an option then I would specify 272 in a dual pane because I think it's a better fit for zone 6. I would be hesitant to use i89 in zone 6 because of the potential for condensation, but plenty of people are doing it.
Thank you both for your input. Working with the contractor now and will post an update once we have some sort of solution.
Off topic: You ordered the windows and the wrong ones were delivered? Or you requested specific windows and your contractor ordered the wrong ones? I'm just curious how mistakes like this happen.
I can't speak to this specific case, but having sat looking over the shoulder of the person inputting the window specs into Andersen's system it's easy to miss these details or not have the details cross into each window of the package.
Going over my last big window order with a fine tooth comb and thinking we all got it 100% correct, I still received all my main floor windows with tempered glass instead of just the ones by the door and bathroom. Not a huge mistake, but it just shows how easy it is to mess up a window order even with the best intentions.
Tim,
In this case we wanted triple panes, but the lead time was too long from the window vendors our contractor used.
I requested quotes on several alternatives (including the Andersen 100's with smartsun/heatlock glazing), then requested they order the Andersen 100's with that glazing.
The windows installed were Andersen 100's without the smartsun or heatlock glazing.
So in this case it was the correct model of windows (including color), but not the correct glazing.
I can't speak to if the contractor ordered the correct version, but the wrong was delivered or if the contractor ordered the incorrect version. Still trying to figure all that out.
Hope that makes sense.