Double-Hung Windows: Triple- vs. Double-Pane Glass
blakeedward
| Posted in Energy Efficiency and Durability on
So I’ve been looking at both Fibertec triple pane and Marvin elevate double pane, both as double hung. Unfortunately client is against casements, and likes double hung. The U-factor on the Fibertec triple vs. the Marvin double pane is only .03 different. My question is for nearly 2000 dollars difference is this small performance difference worth it? And is there another option as far as window type, somewhere in between double hung and casements that performs somewhere in the middle, such as single hung?
Thanks!
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Replies
Unless you are in a very extreme climate, I wouldn't think a 0.03 difference worth it. But what are the actual numbers? I'm wondering why the difference is so small. Are those quoted on the same size window, and both actually the whole window, not center of glass?
$2000 buys you a kW of solar on the roof or 2 kW of solar on a farm - much better use of money.
Per NFRC the best U factor performance for the Fibertech double hung triple pane is U.24, that's with LoE-272 on two lites and I89 on surface 6.
Per NFRC the best U factor performance for the Marvin Elevate double hung dual pane is U.24, that's with LoE-272 on surface 2 and I89 on surface 4.
Dropping the surface 4 coating from the Elevate dual pane changes the U factor to .27 or .03 difference between the Elevate and the Fibertech triple pane with the surface 6 coating.
The triple Fibertech without the surface 6 coating is U.26, which is the same U factor as their dual pane double hung with I89 on surface 4.
Apples to apples the Marvin does appear to have better performance values.
Looking at the Fibertech data some more, the equivalent in casement is U 0.17. It must be that their double-hung frame system leaks a lot of heat through the frame, and Marvin must have that issue solved better.
That was my thought as well
I would say "No, it's not worth it", in this case. I would consider the interior-side i89 coating as an alternative, which might gain you a little performance.
Double hung windows are already about the worst style in terms of energy efficiency due to the way the seals work, and the seals are notorious for leaking over time. I think the additional weight of a triple panel IGU in a double hung window will only make things worse in terms of operation and air sealing of the overall window assembly.
I would put the savings towards additional exterior rigid foam if you're doing more than just window work on this project, as that exterior rigid foam is likely to offer better overall energy savings for the money.
Bill
Let me be the contrarian this is someone’s dream house every winter when they feel a cold draft, they will remember how they let you talk them out of buying better windows to save less than half of one percent on the build price.
Would I spend my money on triple pane window in zone 3, NO way but in zone 7 yes, I would?
Walta
I totally agree that in zone 6 or 7 I am almost always going to recommend triple over dual pane, but not a triple pane that needs to use a surface 6 coating in order to achieve a U.24. If I am paying for triple pane I want a U factor U.18 or better.
For better performance, you can look at an awning window with a fixed element either bellow or above. This can be sized to look pretty much the same as a double hung and seals much better. Some manufacturers offer a push out version which is easier to use.
Does the client want double hung for the way the operate or for the look? If it is for the look, I would steer them towards tilt-n-turn. They are much more air tight and can be designed to look exactly like double hung. I know Marvin makes TnT windows in aluminum clad, but not sure about fiberglass.