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Unread 12-30-2021, 07:11 PM   #1
makethatkerdistick
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Efficient Window Replacement / Mulling Question

Next project at the makethatkerdistick residence is replacement of windows and doors. I've been insulating and air-sealing this house in a lot of places now and have gained a lot of comfort and efficiency. Electricity and natural gas consumption is really low, too, which is nice.

I am starting this thread to see what other experiences people have with choosing particularly energy-efficient windows and doors.

Here's my story so far, including future plans: 1960s North Texas ranch with original single-pane aluminum windows with single-strength glass. The previous owner installed storm windows on top of them. And while they marginally improve efficiency, they also darken the house and make for a cluttered and plainly ugly look. The conductivity of aluminum and the single glazing are giving me at best an R value of 0.9 or even less. Maybe the storm windows boost that a bit, but not much, as the air gap they create isn't completely sealed. There are little gaps here and there where they mount. During weather changes, condensation will gather in that spot, clouding the view for a bit until it dries out.

I have started to replace some windows with good quality vinyl Simonton windows. I chose triple pane for a comfort boost, and I am glad I did. They are true R-5 windows, and the comfort they provide is priceless. Plus, it is nice to have an unobstructed view of the outside world for once. They also feature a low solar heat gain coefficient, which is what you want in a sunny climate like mine. I chose picture windows whenever possible and casement windows where I wanted to be able to ventilate. Those are the best (i.e. lowest) for air infiltration.

Now, some of our biggest windows still are awaiting replacement, and I was wondering if I could do better than R-5. I did some research and found out that there are a handful of companies that build windows to a higher standard than most mainstream American manufacturers. I've set my eyes on Alpen windows from Colorado. Their Zenith series features an all-fiberglass frame and sports either triple glazing or even quadruple glazing. By increasing the thickness of the IGU and using a tempered thin glass in the middle they achieve an impressive R-value of 7.1 for their triple pane and 8.3 for their quad-glazed units. I love their low-profile frames which give more glass as opposed to the typically bulkier vinyl frames. I am quite intrigued to try their stuff. I've gotten preliminary quotes from them, and much to my surprise they are not that much more expensive than the run-of-the-mill R-5 windows of most American manufacturers.

Since I will do all of the work myself, this frees up some money to go the extra mile and get this type of window. It's mostly a comfort decision, as energy savings are there but aren't overwhelmingly big at this point. Having said that, I think a good window provides much more than energy savings. It provides the aesthetic potential of giving you a nice clear connection to the outside, comfort during hot and cold days and a sense of protection from the elements.

I've also started looking into replacing my crappy doors with Provia doors. I love their Embarq which sports an impressive R value of up to R-10 and a dual perimeter seal (which is unheard of among entry doors). I already installed one of their Heritage fiberglass doors and have been really impressed with the quality of the door. Just really good stuff! My local supplier can order them for me, so I don't have to go through a dealer/installer and can install them myself.

Now here is a question for those of you with relevant experience: I will need to mull together a few picture window units to replace an existing bow and bay window. Both windows rest on framing, so no hanging/suspension will be necessary. However, since Alpen Windows doesn't offer factory mulling at an angle, I will have to construct my own. I could just simply prepare a wedge-shaped 2x4 framing member and achieve the angle that way, then rent a brake and bend some aluminum flashing on the outside to cover the gap.
The concern I have is to maintain some sort of insulation in that mulled area. The mull will be the thermal weak spot, and I wonder if there are better ideas to achieve it while preserving a consistently high R-value in that area. Obviously the area needs to be air-sealed to avoid infiltration, and that seems reasonably easy to achieve with spray foam and sealant. I am welcoming any insight into mulling.

The pictures show two window replacements I did recently in my daughter's room. It's a Simonton Reflections series R-5 triple pane. Before I trimmed out the window, I installed 1.25 in of foam strips around the window stool and sides, providing R-8 in this sensitive area to combat thermal bridging of the framing members. This Sunday morning will feature lows in the upper teens, so the insulation work will be put to the test then!
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Unread 12-30-2021, 08:28 PM   #2
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Beginning to sound like the first project after purchase of the makethatkerdistick Manor should have been replacement of the house, Wolfgang.

When you speak of "picture windows," I'm assuming you mean fixed glass units, yes?

Mulling fiberglass frames, unless you are prepared to create matching fiberglass mullions, would, in my limited world of resources, seem limited to wood or steel framing that would then be flashed and trimmed as necessary. Your quest to limit heat transfer would rule out the steel, so I couldn't offer you any clever suggestions better than your planned wood mullion. Not perfect, but better than average, and an easily available material that's easy to work with.

I know a place in San Antonio that could mill them from medium density polyethylene, but then you have the problems of fastening and I don't even know the solid plastic would be significantly higher in R value than the softwood. Actually, I don't even know it's not lower.

I recognize that you're aiming for the absolute technical best you can achieve here, but I think you gotta consider the practical limitations as well.

I believe you're familiar with the customary charge for all that, eh?
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Unread 12-30-2021, 10:11 PM   #3
makethatkerdistick
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Softwood has an r-value of 1.4 per inch. I think you are right that engineered materials might not have an advantage when it comes to the ability to hold fasteners and insulate at the same time. These properties seem mutually exclusive. The sales person at Alpen Glass is a former window installer himself and suggested that wood might be my best choice. There are generally no customizable fiberglass trim elements. Oftentimes, PVC or metal are chosen because they are easier to shape. When vinyl window makers mull bay or bow window units at the factory, they often insert steel rods to hold the individual elements in place. The surrounding gap is then sealed as dead air space, which has decent insulation value (provided it is sealed efficiently).

And yes, picture window = fixed unit. Seems a lot of thermal loss can happen in the transition area between frame and IGU. Historically, European window makers have been more successful at better frame designs and also lower infiltration rates. If you look at a lot of the American companies, their frame profiles have been the same for a long time, limiting the performance that can be achieved. Picture windows naturally always perform best, but operable units that feature a closing mechanism that creates seal compression are the next best thing (casement, awning, hopper windows).
I grew up with the European tilt and turn style windows. They are great. Alpen makes such a model as well, but it is vinyl, not fiberglass. There is also Zola Windows in the U.S. that offer great aluminum windows with a thermal break between both sides, but they have their units built in Europe. Intus from Lithuania is another choice with good distribution in the U.S. if you compare these windows to Pella, Marvin, Simonton, Andersen, they always perform better.
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Unread 12-30-2021, 11:53 PM   #4
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Visionwall tech has some unique windows. Rather than middle of the window ratings, these can produce an honest R7 across the whole window. One thing, especially on larger windows that use sealing and argon gas, theirs do not, so don't degrade over time as those with argon break their seal and leak. Also, by not being sealed in the same manner, the panels don't bow in/out and potentially distort the image and reflections. That's a bigger issue on larger windows. The downside is that these windows are considerably thicker than more conventionally built windows.
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Unread 12-31-2021, 09:54 AM   #5
makethatkerdistick
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The R-values I had used are all for the whole unit, not just center of glass values.
It is great that Visionwall offers such R-values with only air as insulator. I assume that is made possible by the low thermal mass of the suspended heat film in the middle and the wider gap. Alpen offers this heat film technology as well, but I am nervous as there have been failures in the past with this. From what I have heard, the film can crinkle, leading to unwanted visual distraction. They have introduced the thin glass option as an alternative to their heat film technology, and I prefer that from a longevity standpoint.

Yes, all seals will eventually fail. And when they do, condensation buildup on the inside is a possibility, regardless whether you use air or argon or krypton. In the field, unless the seal fails dramatically, the average leakage rate is about 1% per year, so a window’s performance will slightly diminish over time, but you will always get higher insulation values with a gas fill, especially if you use krypton.

Jim, do you know whether Visionwall also serves the residential market? Seems to me their applications are mostly commercial? If not, I might be interested in learning more. Regardless, I think that the technology among high-efficiency window makers is fairly similar. The rules of physics are all the same for them.
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Unread 12-31-2021, 10:06 AM   #6
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Not to mention that the Krypton would keep even Superman out of your house, yes?
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Unread 12-31-2021, 10:17 AM   #7
makethatkerdistick
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I posit that there is a distinct difference between krypton and kryptonite, the latter being a crystallized substance.
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Unread 12-31-2021, 10:25 AM   #8
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Picky, picky, picky!
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Unread 12-31-2021, 05:48 PM   #9
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Interesting discussion. A quick side note: The windows I’ve seen with a film layer in the middle of the panes to help with reflecting radiant energy are noticeably darker. They are like lightly tinted windows. Do these triple and quad windows you speak of exhibit less light transmission as I’ve described? Or are they fairly bright?

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Unread 12-31-2021, 11:41 PM   #10
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Visionwall caters more towards commercial buildings that are sheathed in glass, but they can work in residential situations.

I don't know if they still make them, but they did have a series that was configured similar to those more common in Europe...the handle turned 90-degrees allowed the whole window from the top to tilt in for ventilation, but the way it was done, unless it was really windy, wouldn't leak in a rainstorm, so that was neat. I had windows configured like that when I lived in Germany and really liked them. From the closed position, if you turned that same handle 180-degrees, it would open like a door so that made cleaning them a piece of cake.

They do have sliders that can be configured up to 13' tall.

You'd have to call or request some literature to find out their full line. I think they originated in Switzerland but have been in the NA market for probably 25-years or so.
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Unread 01-01-2022, 11:17 AM   #11
makethatkerdistick
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Hi Jim, yes, I grew up in Germany and am familiar with the tilt and turn windows. Alpen and Intus offer those for the North American market. Since I am really insistent on fiberglass frame, I am forgoing them. I have an area that gets extreme sun exposure, and I just think the fiberglass frame will perform better in that area, even though the Alpen and Intus PVC frames have internal steel reinforcement (unlike the mainstream vinyl windows that do not).

There is a prevailing theory that the similar thermal expansion and contraction coefficient of fiberglass is quasi identical with the glass unit, that this will retain the integrity of the seal between frame and glass over the years
Sliders are definitely out of the question due to their poor infiltration performance.

Bubba, yes, the more panes you add, the darker a window gets, especially if it has Low E coatings on two or more glass panes. It's a tradeoff. The VT (visual transmittance) rating will tell you how bright a window is. If you live in the north, you most likely don't want Low E coating or want a lighter coating, so you can realize thermal gains when the weather is cold and sunny. Window glazing should really be individually chosen for the climate zone and also the orientation/exposure on the building proper. So much to choose from to optimize your house's thermal performance.
I suppose that down here in the south Low E coating is always a good choice. Maybe if you have lots of overhang and have north facing windows, you could potentially choose clear glass.

The Low E triple panes I have certainly have a little "tint". I am hesitant to call it that. It's a slight greenish shimmer that filters out some of the visual red spectrum, so colors appear more neutral and slightly less warm. It's not a true tint. On a bright sunny Texas day it actually looks kind of nice. The cool thing is also that it gets rid of virtually all of the UV radiation as well. If you have nice books, nice furniture etc., you will not see them get bleached by the sun at all. And if the sun hits your window glass directly, only about 20% of its energy is absorbed and makes it into the building as thermal energy, whereas 80% is reflected before it enters. With regular glass, this is the other way around (80%+ is absorbed). Huge benefit in a predominantly cooling climate.
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