Comparing Window performance
Lizzieplants
| Posted in Energy Efficiency and Durability on
I am trying to compare apples to apples on various triple window brands. When folks here quote the U value of a window I assume they are talking about Uw (whole window). I was told by a vendor that that value varies with the size of the window. What window size are people assuming when they say the U is a certain value?
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Replies
Elizabeth,
Here in North America, if you are shopping for windows, the best approach is to ask the window dealer for the NFRC rating on the window. NFRC ratings are always whole-window ratings. These can be compared from manufacturer to manufacturer.
Be wary of fly-by-night operators who quote "center-of-glass" U-factors or SHGC. These can't be compared to NFRC values, and these values are always unrealistically impressive.
The NFRC rating of a small window will not be identical to the NFRC rating of a larger window with the same type of glazing. Ask your dealer to give you the NFRC rating for a window of the size you are interested in. If the dealer can't do that, but can only provide the NFRC rating for a standard size, then you may need to compare that standard size between manufacturers. Just be sure you understand what you are comparing.
Thanks, what NFRC rating am I looking for to use in a passive house, similar to the good German windows?
Elizabeth,
Here are some articles to read:
Passivhaus Windows
Choosing Triple-Glazed Windows
All About Glazing Options
I didn't see Intus in the articles. What is your opinion of the Intus vinyl windows? The prices seem very reasonable compared to the other options (a fixed window price between $30-$40 s.f. and operable between $40 - $50 s.f.) Is their vinyl really better than the vinyl used in most windows?
The information they sent me is:
Glazing options:
Glazing Low SHGC: SHGC=0.37, Ug=0.088, VT=55.2
Glazing High SHGC: SHGC=0.62, Ug=0.106, VT=73
Glazing High SHGC: SHGC=0.494, Ug= 0.106, VT=70.3
Thanks
Elizabeth,
Here's a link to a GBA article discussing Intus windows:
New Green Building Products
It's hard to compare vinyl quality between window manufacturers. Most reputable vinyl window manufacturers are now using high quality vinyl that should hold up for decades.
Remember, the "Ug" numbers that Intus gave you are not NRFC whole window U-factors, they are center of glazing numbers. Try to obtain NFRC numbers from Intus; if they don't have them, you'll have de-rate them to compare them to NFRC U-factors.
the 'NFRC' rating to meet passivhaus varies greatly by region.
a number of folks in the PH community are really gravitating towards Intus's uPVC windows. i'm not sure of the composition of N.A vinyl windows, i don't imagine it's very different - but the EU does tend to have stricter environmental regulations.
if trying to avoid PVC, zola windows (wood, rep is in colorado) may be a feasible alternative, depending on price point.
The NFRC numbers for Intus' Eforte Tilt/Turn as well as fixed windows are available...
http://search.nfrc.org/search/cpd/cpd_search_detail.aspx?cpdnum=IWW-M-2
http://search.nfrc.org/search/cpd/cpd_search_detail.aspx?cpdnum=IWW-M-1
Standard NFRC size for tilt/turn windows is 1200mm x 1500mm
Standard NFRC size for casement windows is 600mm x 1500mm
Standard NFRC size for fixed windows is 1200mm x 1500mm
For glazing comparison, the standard high solar heat gain triple glazing available from most US window manufacturers is Cardinal LoE-180 / clear / LoE-180. Cardinal's Center of Glazing numbers are:
1" triple glazing: SHGC 0.56, Ug = 0.18
1 1/8" triple glazing: SHGC 0.56, Ug = 0.15
1 3/8" triple glazing: SHGC 0.56, Ug = 0.13
Also:
3/4" clear / LoE-180 double glazing: SHGC 0.69, Ug = 0.26
The thicker glazing package is very close to the european glazing numbers, considering they have different testing regimens.
Source: http://www.cardinalcorp.com/technology/reference/loe-performance-stats/
I had a chance to get up close and personal with Pella's new 350 vinyl windows this last weekend. I have never liked vinyl windows due to the cheap feel and look, and the bad sounds they make! However I must say, I was extremely impressed by this window. I was a casement, and the seams and vinyl was very thick and strong. The seams in the corners are ground smooth so you hardly even see them. They actually have a profile to them to they resemble more of a wood window. The crank was the typical Pella folding crack with stainless steel track and was very smooth. It was a triple pane option with a u of .19. The fixed version is .17. It has double seals on it. It is the only window of their lines to have a double seal. They also have a Sun-glass option (can not recall the name of the glass) but it offers higher SHG numbers. Still not as high as they should be (high .30s) but still not bad with a u of .20.
I have been sold on fiberglass windows from Canada, however these are definately something to consider, especially since they are slightly cheaper and made in my back yard with a quick turn around.