Another triple-pane thread…they just are not making a lot of sense
First off, I have read about every post, blog, and entry made on here about triple pane windows, have talked with the companies, received bids, etc. So with that being said…
On paper, they do not seem to make any sense now matter how I look at it. I have ran numbers in multiple programs from as simple as RESFEN to high end stuff in my Revit MEP and other modeling programs. I am happy to say all of my loads and energy costs are very similar from the free programs to the high end however.
Looking closely at full fiberglass options, I have compared Pella Impervia, Marvin Ultrex, Milgard Ultra, Inline, Fibertec, Thermotech and Serious. The Marvins have the worse numbers (in terms of infiltration, U-factor, and SHGC) out of the group, so I tossed them. Serious, while good numbers, I am hestiant, like many, of the films so I will make it easy and toss them too. Thermotech has the best numbers of the group, but the price came in pushing double any of the rest, so they are out.
Inline and Fibertec are basically the same number and cost wise, so to be easy, I will look at Inline vs Pella Impervia.
Let’s start with the facts. THese are also the numbers I used in the programs:
Pella: Dual pane lowE, U=.28, SHGC .30, air infil= .05, VLT 57 for all north glazing
Dual pane LowE w/ NaturalSun, U=.30, SHGC .57, VLT 64 for all south glazing
Inline: Dual pane lowE U= .31, SHGC= .50, air infill= .03 VLT .51 for south glazing
Triple pane, south glazing, U=.22, SHGC= .39, VLT .43
Triple pane, north glazing, U=.20, SHGC= .25, VLT .39
GIven those numbers, Pella is not looking to shabby at all. Lets add in that Pella is about $2500-3500 less. They are about 2500 less if you use Inline dual on the south and triple on the north, and 3500 less if you use triple on both.
Energy savings, on average from my programs, are putting out a super low $70 a year. I only have north and south glazing, so it makes calcs easy as well. So assuming they are a 30+ year payback, are my findings typical for some? I know based on responses from Robert Riversong he seems to really favor the Impervia line. I would agree as they perform better on southern elevations, and not far off on the north.
I understand the human thermal comfort argument….but what else am I missing?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part