272 vs 366 glass? Please help.

albertdcApril 21, 2011

In case you haven�t seen my other threads, I am about to replace 25 windows in my house. It is a 1989 Stucco home in Utah. Current windows are double pane, but all the seals are failing and the windows have crummy aluminum frames that transmit cold and completely ice up in the winter. Thus the replacement saga begins.

I am strongly leaning towards the Marvin Integrity line. I am deciding between 272-Argon vs 366-Argon glass. Here are the stats:

272-Argon: U-value 0.31, SHGC 0.33, VT 0.57

366-Argon: U-value 0.30, SHGC 0.20, VT 0.51

We have local energy rebates which require 0.30 or better, so that would push me to the 366 glass. However, the rebates are small in the scheme of the whole project, so I want to be sure that the 366 glass is the right choice in its own right..

We have several 5x5 foot windows facing west and those rooms roast in the summer. We also have a 7x5 foot window facing west. It is my understanding that the 366-Argon glass is a no-brainer for these, right?

How big of a difference is a VT of 0.57 and 0.51? Since we have a lot of large windows with beautiful views, how concerning is the darker tint of the 366 glass? Is it becoming standard to do the whole house with 366 or will it feel like we are wearing sunglasses inside?

Thank you for any feedback.

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windowsonwashington

272 on the South facing elevation.

366 in the remaining sides of the home.

    Bookmark   April 21, 2011 at 10:45AM
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albertdc

WindowsOnWashington - Thank you for your input. I've tried reading a bit about this, but I am obviously still a bit confused, thus the posting here. Can you tell me a bit more - why 272 on the South facing windows? (In my case, that is only 2 windows as the bulk of the winodws face east or west, a few north, and the garage + 2 windows south. However I am curious to learn the rationale, so if you or anybody can give a brief lesoon I would greatly appreciate it!).

Is the 366 noticeably darker?

    Bookmark   April 22, 2011 at 1:00AM
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skydawggy

He's recommending the 272 because of the higher solar gain. In a heating dominated climate, this will be beneficial to you during winter. The U-factor of the 272 and the 366 are almost identical so for passive insulation purposes, they would net the same results. IMO 366 glass should only be used in a cooling dominated climate such as Texas, Florida etc. In fact, I would normally recommend going with the 181 glass on the southern exposures. There is a noticible difference in visible light transmittance between the 366, 272 and 181 glass. I would highly recommend you see an actual sample of the different glass units before deciding.

    Bookmark   April 22, 2011 at 8:37AM
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albertdc

Great. Thanks. Yes, I will try to see samples, but sometimes it is hard to predict how the sample will translate into the whole project when that window is actually in the house.
My house in Utah needs heating in the winter, but major cooling in the summer due to the hot temps and very bright sunlight. The sun in the summer feels like the sun in the movie "Chronicles of Riddick!" I think I would certainly want to decrease the solar gain for the West-facing windows. For that, 366 is the right choice, right? I will certainly consider sticking with 272 for the rest of the house.
Thank you.

    Bookmark   April 22, 2011 at 1:32PM
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mydreamhome

Same question, different state...

Central NC
House faces due south
Back faces due north (lots & lots of glass w/ 2/3 of the windows under 12-16' deep porch)
2-3 windows on either end of the house facing east & west.

Also Marvin Integrity except family room that will have Marvin Ultimate doors (2 functioning flanking 3 fixed) w/ transoms above.

Thanks!

    Bookmark   April 22, 2011 at 2:22PM
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windowsonwashington

The windows that are under the deep porch on the South side should get a high solar heat gain glass like the the Cardinal 180. The unshaded windows could stay with the 180 or go to a 272.

On the North side, you could still stay with a high visibility coating like the 272 on the porch covered units and go with a lower SGHC unit on the unshielded units like a 366.

All of these glass packages could be combined with the i81 hardcoat package.

Marvin uses the Cardinal family of glass options.

Here is a link that might be useful: Cardinal Glass

    Bookmark   April 22, 2011 at 10:23PM
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mydreamhome

You are a font of valuable information as always WindowsonWashington. Thanks so very much!!!

    Bookmark   April 23, 2011 at 11:26AM
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shaqd

added benefit of the 366 is added UV protection

    Bookmark   June 8, 2011 at 7:23PM
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windowsonwashington

Standard low-e blocks 80% of most UV spectrum already.

The drop in VT on the 366 helps more to control fading than the additional UV drop if I were a betting man.

    Bookmark   June 9, 2011 at 8:56AM
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three_acres

We are about to order some Marvin windows too only from the Ultimate line.

For what it's worth here in WI my calculations clearly show that using all 366 glass is the best option in our cold climate. The 0.01 lower U-value saves more energy than the 0.1 increase in the SHGC on our large south facing windows. I design HVAC systems for a living so calculating heating and cooling calcs is part of my job. My sales rep said I should use 272 glass on the south facing windows also but I came back to him with my calculations using a software that takes into account the yearly weather conditions and movement of the sun for all 8,760 hours in a year.

So in cold climates go with all 366 for increased energy savings!

    Bookmark   June 9, 2011 at 6:49PM
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oberon476

WoW,

You would win that bet.....

    Bookmark   June 10, 2011 at 10:33AM
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windowsonwashington

I will defer to Oberon on that calculation, however, there is no accounting for the loss of VT with the Low-e 366 in that equation.

Your math also flies in the face of the studies I have read.

See the link below

Here is a link that might be useful: Zero Energy Windows

    Bookmark   June 10, 2011 at 2:38PM
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three_acres

Yes I understand Oberon is considered the authority on this forum but these numbers are based on software calculations from Trane Trace 700 (one of the leading load calc softwares on the market). The software takes into account the angle and movement of the sun in every hour of the year. What do you use Oberon? I also failed to mention I create energy models for LEED buildings too. This software has been approved to use for LEED energy models.

I didn't forget to input the VT I just didn't get into all of the details in my last post. Here are the numbers I used for my window library files:

Double pane
U-factor = 0.29 (or 0.30 for the 272 glass)
Shading coefficient (SHGC/0.87) = 0.23 (or 0.34 for 272)
VT = 0.47 (or 0.52 for 272)
Inside visible reflectivity = 0.227
Solar transmissivity = 0.504
Inside solar reflectivity 0.182
Outside long wave emissivity = 0.84
Inside long wave emissivity = 0.84

The last 5 numbers I haven't been able to find for either of the glass types. If anyone has that info that would be great! I just used the standard double pane values for those and kept them the same for both calculations. I have mostly gliders in my house with a few casement and fixed windows so I used the glider values. Using those values also gave me the worst case scenario.

Using the 366 glass on the whole house gave me:
-52,884 Btu/h Heating Load
12,984 Btu/h Cooling Load

Using 272 glass for the whole house gave me:
-53,168 Btu/h Heating Load
14,197 Btu/h Cooling Load

Using 272 glass on only the South & Southwest facing windows in the dining room and living room (which are all large & typically bring in a lot of light) gave me:
-52,994 Btu/h Heating Load
13,425 Btu/h Cooling Load

So all in all it's not a huge difference but the cooling load is still higher with the 272 glass on the south facing windows vs the 366 glass. With the cost difference between 272 and 366 being very minor we're going with all 366 glass.

Correct me if I've forgotten to include anything Oberon.

    Bookmark   June 13, 2011 at 7:04PM
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windowsonwashington

I was speaking more to the offset in visible transmittance numbers and the customer's aversion to that darker window.

    Bookmark   June 15, 2011 at 5:39PM
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oberon476

My reply to WoW only related to his comment on fading and nothing to do with energy performance.

And while my comment wasn't meant to be flippant, it was intended to be in fun as part of the conversation as I took WowW's original comment to be as well.

Do I KNOW for certain that the slight darkening of 366 versus 272 has more of an effect on fading than does the improved UV-blocking performance? Nope. So I probably should have said that "I think" he would win that bet...

And while LoE3-366 does have outstanding UV-blocking numbers versus LoE2-272 (95% versus 84%) I suspect that most people tend to overestimate UV and underestimate visible light when thinking of stopping potential fading; as is pointed out pretty clearly using the fading comparison chart from Cardinal's Residential Glass Guide, page 20 (see WoW's earlier link).

Is the chart a definitive reference to support either idea? Again, not really. But it does offer some excellent comparison data related to fading and the use of laminated glass (which blocks upwards of 99% of UV), LoE coatings, and tinted glass.

    Bookmark   June 16, 2011 at 5:32PM
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oberon476

three acres,

It appears that the first three values that you listed (U-factor, SC, and VT) are window numbers. The last five are glass numbers.

The glass-only figures for both 272 and 366 are available on the Cardinal web site with the exception of coating emissivity.

Assuming 3mm or 1/8" glass, the long wave IR emissivity for 272 is .96 and for 366 is .98.

I have used LBL Windows 5 in the past, but typically if I need to do any computations for online posts I pull out a piece of paper and my calculator since I am not trying to create energy models, I am simply (hopefully) giving people a few basic facts and ideas so that they can pursue more information and (again hopefully) a little more understanding.

    Bookmark   June 17, 2011 at 12:53PM
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yahoo_yahoo_com

As a consumer researching info I will say this. A bunch of grown as men bickering back and forth like a couple of f@ggots doesnt help anyone. Stick to the facts and giving advice and cut out all the teenage girl back and forth....you are men right? nobody gives a 5hit who thinks who is better then the other. We only care about the questions we are trying to answer for ourselves. Leave your real housewives drama out of it. Thanks for nothing doucheb@gs!

    Bookmark   July 31, 2011 at 11:36AM
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skydawggy

Irony score: 10 out of 10.

    Bookmark   July 31, 2011 at 12:47PM
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oberon476

+1 Skydawggy

    Bookmark   July 31, 2011 at 5:36PM
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windowsonwashington

Laughing uncontrollably right now.

    Bookmark   August 1, 2011 at 12:08AM
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