Logic Vs. Pella
Good evening folks! I’m currently in the process of building a PGH, and I had a question regarding window selection. I’m new to the high performance world, so I’ve gotten a quote from Pella and Logic. I was really surprised to see that a Pella 250-series vinyl triple glazed has better specs than a Logic 272/cl/2180 triple glazed tilt & turn. I’ve specified Pella more times than I can count as a residential PM, but never their triple glaze. I’m going to post the specs below comparing the two because I’d really like some feedback on the two. Would love to have tilt & turns in my house but if Pella outperforms them, it’s pretty easy to go with them? Thanks, and have a great weekend!
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
That Pella window has a U-value of 0.23 which is worse than the other screenshot of 0.15. Maybe you are forgetting that U-value is 1/R-value. So lower is better, unlike R-value where higher is better. I recommend pulling the values from the NFRC directory website for the model you are interested in to make sure you are looking at apples-to-apples. The Logic screenshot you shared, for example, has a highlighted row for “glass only” which is meaningless. Only the fully installed U-value matters.
Yessir, I'm aware of the U-factor difference. My main concern is the SHGC of the Logic windows, because I plan on a lot of southern facing glazing for passive solar gain, whereas you can see from the screenshots, Pella has a much higher SHGC.
Don’t let the SHGC, which is only useful in winter, drive your decision to install a lower performance window. Keep in mind the U-value helps you all year long. And U-value is what keeps the cold out in winter. You wouldn’t need as much SHGC if you could just keep the cold out in the first place. Something that is repeated on this forum a lot can work as an analogy here: people like to talk up radiant barriers in warm climates and claim that they add a lot of “insulation value”, but the truth is if you just increased the R-value of your insulation (or increased thickness of the same insulation), you would have better results than adding a radiant barrier. And it would provide that benefit year-round. You’re kind of thinking the same way.
I think a BEopt model would be useful for you to see the impact of different window characteristics on your yearly average energy bills. It’s a free program you can download from the NREL website. That should help guide you as to what the two windows will do and which one would be worth it relative to cost and energy savings as well.
Also, you never posted your climate zone so I did not realize SHGC was important to you in the first place.
Thanks for all the information I appreciate it! I'm in Massachusetts, so climate zone 5.
If you want to maximize SHGC you should be looking at 180/cl/180
Deleted
Logic glass-only performance numbers, including those for 180/cl/180 of U.13, SHGC .56, and VT 70% were taken directly from Cardinal's web site. I don't know where their other numbers come from since I didn't see any references on their website and couldn't find them in the NFRC.
For an apples to apples comparison:
Your Pella quote is for 180/cl/180 - U.23, SHGC .42, VT 52%
Logic's tilt/turn with 180/cl/180 - U.16, SHGC .38, VT 47%
A U.16 for a triple is a good performance number, while a U.23 (IMO) is unacceptable even for a double hung.
The higher SHGC and VT for the Pella is simply the result of a higher percentage of glass to frame in the Pella vs the Logic.
But since you are considering a Logic window with 270/cl/180, then you also have to factor in that LoE-270 has a lower SHGC and VT by design compared with LoE-180, something that has to be factored in to the performance comparison as well.
I am not a particular fan of Pella windows, but probably also worth noting is that the Logic window, per their website, has a 1o year warranty, glass included, while Pella has a 20 year on glass and 10 for the rest.