Getting the Right Low-E Window Coating
I’m needing to replace windows very soon. My house is perfectly placed to take full advantage of the sun in the winter on the south side yet not overheat in the summer. I don’t have A/C and don’t feel I need it. I’m having a hard time determining if it would be better to have Cardinal low e 180 inside the panes for the south side windows or just hard coat on the glass facing the interior of the house in order to retain heat in the winter without blocking too much sun. Too much sun is not an issue in the summer. Worried about an increase in haze with the hard coat. Worried about blocking solar in the winter with the low e 180. There are no windows on the east or west sides. I’m assuming typical low e 180 would be appropriate for the north, but maybe hard coat on inside pane would be better there too? Location is Colorado. Would appreciate any information that might increase my understanding and make this decision easier.
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Since you are planning to replace your windows, this article might be helpful: Buying Windows.
Also, there is a lot of useful information in this Q&A thread .
And here is A Buyer’s Guide to Windows from Fine Homebuilding.
Thank you! So far, I'm comfortable with my decision to get Milgard fiberglass double-paned windows (probably single hung throughout except for an awning in the kitchen). But this glass thing is driving me around the bend. This house was site situated for passive solar benefit, and I don't want to ruin that with the wrong glass. It also has lovely views, and I don't want to ruin those with the wrong glass. Before setting off on this renovation venture, I never realized windows were so complicated.
One document I found helpful in trying to make decisions on window low-E coatings was https://www.cardinalcorp.com/source/pdf/Technical_Glass_Guide_Web.pdf -- good data on the various coatings and their performance
In my situation, I'm going with LoE-180 in most locations, and LoE-272 in a couple specific locations where I have lots of sun and no shading. (Note that I'm accepting the fact that adjacent windows with different coatings will probably look slightly different -- but in the mentioned locations I'm already using a reflective film on the old windows, so I'm accepting that)
Thank you. I will check out Cardinal's info. via your link.
Glass thickness and airspace width will affect the numbers, but assuming double strength glass and a 7/16" airspace a clear/clear configuration will net you VT 82%, SHGC 78%, and CoG value of U.48.
Compare that with an IGU using LoE-180 on surface 3, VT 79%, SHGC 71% and CoG U.26 (including argon fill).
Clear/clear with I89 on surface 4 is pretty much identical with the 180 on surface 3, but I89 on surface 4 will lower condensation resistance closer to clear/clear and 180 on surface 3 will raise condensation resistance significantly over clear/clear glass.
You won't notice either 180 or I89 on your glass, but traditional hardcoats do result in glass haze, how much depends on the coating. Pilkington Energy Advantage is probably the least haze of any hardcoat that I am familiar with. And any hardcoat on surface 4 will lower condensation resistance as well.
Numbers are available on Cardinal's web site if you are interested in checking them yourself
Just when I thought I'm getting this, condensation comes into the picture! Is condensation an issue in a very dry climate? Or does it have nothing to do with climate? I do not humidify my home via the central heating system. I just have houseplants, and bowls of water, and I hang most clothing inside to dry (it dries really fast here). Towels and heavier items I put in the dryer.
Also, there won't be argon. So that will change the numbers. But I think you are telling me that there is no advantage to getting the hardcoat glass for the interior pane vs. the standard 180 low e between panes?
I'm also confused about 180 vs. 189. Is 189 the hard coat? I understand 180 to be the standard made-for-passive-solar coat applied to the class and placed on the inside of the panes. Please correct me if I'm wrong.
If I understand right you are debating between a conventional cold-climate low-e setup, cardinal 180, and a configuration with a low-e coating only on surface 4 (facing the interior of the hosue) and not on surfaces 2 or 3. I don't think anybody makes that, at least not standard. And for good reason. The solar heat gain (SHGC) would be the same as the cardinal 180, and the U-factor would be quite substantially worse.
The reason the low-e coating goes on surfaces 2 or 3 is that it can then team up with the argon fill to make the heat transfer between the panes low. A low-e coating on surface 4 blocks radiation transfer from the room to the glass, but the heat can still easily get there through convection in the room air.
Yes, thank you! You understood me correctly -- no easy feat as I'm struggling with window terminology.
Because I'm getting Milgard fiberglass windows, there will not be any argon gas. I'm at high altitude and where the windows are manufactured is not.
Are you saying that a hard coat glass on the interior will allow for more heat transfer out of the house than low e 180 applied to the glass between the panes? And would that still be true without the argon?
Yes, that's what I'm saying, and yes, it's still true without that argon.
Thank you -- that's very clear. So, considering the tiny difference between the amount and quality of light coming in, there really is no reason not to do low e 180 alone on the south side as far as I can tell (especially if hard coat does not come without it anyway).
Dot,
Some window glass basics that you might already be familiar with, but just in case....
Window glass surfaces are labeled 1-4 (or 1-6 if you have triple pane). Surface 1 is the outside of the outside lite, the one you can touch if you are outside. Surface 4 is the inside surface of the inside lite, the one you can touch inside your home.
There are two types of coatings, hard and soft, something I know you have some knowledge of already. Softcoats, also called sputter coatings, must be encapsulated between the lites of an IG (or laminated) unit because they are fragile and will be damaged and will corrode if exposed. Hard coats are usually some variation of tin oxide (some with titanium as well) that can be exposed on the glass surface.
In general softcoats work better than hardcoats and so are much more common, also as you expressed concern about, hardcoats are not as clear and can look hazy especially in direct sunlight.
I89 is a hybrid of sorts because it's a sputter coat that can be exposed like a hardcoat, but it's manufactured using softcoat technology. Because of it's sputter origins, I89 performs as well or better in hardcoat applications, but without the haze often associated with hardcoats.
Softcoat LowE coatings can be applied to either surface 2 or surface 3 in an IG unit. Surface application does not affect the U value or visible light transmission, but is does affect the Solar Heat Gain Coefficient. ANY softcoat applied to surface 2 will have lower SHGC versus surface 3 application. The SHGC I listed for LoE-180 in my earlier post was a surface 3 application, while the numbers for I89 (eye 89) was a surface 4 application.
I89 was designed as a surface 4 coating to be used to improve glass U value. In simplest terms is does this by reflecting radiant energy away from the glass what would otherwise have been absorbed by the glass. Reflecting the radiant energy away from the glass has three effects.
First, the glass will be colder because of reflecting rather than absorbing the radiant (heat) energy. Obviously colder glass has the potential for condensation on the glass versus warmer glass and this does lower the condensation resistance factor. It's worse at the edge of the glass and not too bad center of glass (center of glass is the full sheet except for 2 1/2" in from the edge which is the edge of glass).
Window condensation is all about your indoor moisture level and not outdoor. You can live in the a dry environment but if its cold enough, and your indoor humidity is high enough, you will get window glass condensation.
Second, and counterintuitively, because the coating reflects heat back into the room, anyone sitting in front of the window will be warmer than they would with a conventional window.
Third, the coating improves U value measurement of the window, again because of the reflecting heat back into the room thing.
LoE-180 was designed as a 3rd surface coating, so that's where it SHOULD be located in the window. I capitalized should because window companies are much more accustomed to placing softcoats on surface 2 and they need to pay extra attention to getting coating location correct when glazing to surface 3.
Hope that helps....
Oh thank you!! I love this website! Your comment has greatly increased my window knowledge (and, consequently, greatly reduced my anxiety). I didn't know that I89 (NOT 189!) is a hybrid coating and less hazy. And thank you so much for explaining the numbering system. Also, your condensation explanation is very clear and helpful. Based on what you say, I'm pretty sure condensation would not be a problem no matter what glass I choose.
Am I looking at this logically when it seems to me that I89 would be a good option for the south-side windows, and LowE 180 would be most appropriate for the north-side windows? I should probably add that I'm on a bluff where the high-altitude sun exposure is amazing. But with the house placed as it is, the sun coming through the windows on the south side is much stronger in winter than in summer (thankfully). The north light is pleasant (but not warming, of course). Do not wish to make the north side darker than necessary. I'm assuming UV protection would be less with the I89 than the LowE 180, but I'm not concerned about that. It might be a plus in terms of plants being on the south side and their probably wanting/needing full-spectrum light.
Please let me know if I'm way off somewhere in my take on this.
Is your primary concern maximizing the energy efficiency of the windows, or are you worried about solar gain (SHGC)? The more aggressive LoE coatings (272, 366) mostly reduce SHGC in terms of benefits, but they also noticeable darken the windows. I'm not a fan of 366 in partricular because of this. 180 and i89 is a great combo on a double pane window. If you want additional cold weather performance, you can step up to a triple pane if Milgard has that as an option -- but remember that you really need full thickness (1-3/8") IGUs for maximum benefit from a triple pane assembly.
i89 is more for keeping heat in than for keeping sun out. If you are really concerned with the sun on the south side, you may want to consider one of the more aggresive coatings on that side -- just don't mix coatings on different windows that are simultaneously visible since there will be a noticeable visual difference between them that will look weird. i89 and loE 180 on the North side is likely to be a great combo.
Bill
Bill,
Light -- quality and amount -- is very important to me. But energy efficiency is, too. But I'm aware there will need to be trade-offs made. LoE 180 will maximize light and slow solar gain heat loss after dark in winter, and I'm thinking that's about as good a balance as I'm going to get.
Glass thickness is something I have not even looked at yet. I've got a bunch of stats from Milgard, and I will check to see if they even mention that.
Not at all concerned about repelling sun on the south side. This house is set on the land in such a way that the sun blasts in through the windows in the winter when I want it to, and doesn't do that in the summer which is perfect. I am very concerned about losing too quickly the warmth gained from the solar in the winter time.
So, as I read your excellent comment that further clarifies this whole glass issue, I'm wondering why loE 180 would be necessary at all on the north OR south side of a home like mine that is site situated for passive solar. I89 on its own seems to me to be the ideal choice IF it's available on its own. But someone else pointed out that it may only come combined with loE 180. If that is the case, then, in your opinion, would the best choice become loE 180 by itself on the south side and loE 180 combined with I89 on the north?
One clarification: I89 is the name of the surface 4 coating. If you specify I89, that is usually in combination with the LoE 180 on surface 3. So the options are LoE-180, or LoE180 + I89. You are unlikely to get able to order I89 alone.
For those two options, LoE180 has SHGC of 0.69 (center of glass) and LoE180+I89 has SHGC of 0.62 (center of glass). So if you want to max out the SHGC on the south side, you'd put the LoE180 there. But 0.62 vs. 0.69 isn't a big difference, and you might want to go with LoE180+I89 everywhere if condensation isn't a concern.
Charlie,
Just saw your statement that I89 may not be available on its own!!! Had been reading the replies from last to earlier. Thank you so much for clarifying that. I've may have wasted lots of mental energy on a decision that's already made simply by what is available and what isn't. I will definitely ask the window company about that today.
Your explanation of where the combined I89 and LoE180 would be advised is also very helpful. The fog is lifting! Thanks again! If the window company tells me that I89 is not available on its own, then I would go with LoE180 over the whole house unless someone here tells me that's a bad idea. Just don't want to lose too much light (one of those energy efficiency vs. aesthetics trade offs).
The one way to get exact answers is to set up your place in Hot2000 and run each coating option:
https://www.nrcan.gc.ca/energy-efficiency/homes/professional-opportunities/tools-industry-professionals/20596
I've done this before for my south facing clerestory windows, the best SGHC and U compromise was a couple of percent lower energy use over the year, the difference between options was actually small.
Unfortunately this "optimal" combination is not the best for comfort, you can really feel the cold on those clear but cold winter nights. I should have gone for some reasonable SHGC value with the lowest U factor possible.
I wouldn't worry about the SGHC, get the best U factor windows you can buy. If you have any large fixed windows, upgrading them to triple pane might be worth it. I would also look at sourcing local windows that can be argon filled.
Akos,
What are "clerestory" windows? Is that a clear, uncoated window? That is the first time I've come across that word.
Yes, I am just now realizing that the difference between options really is small. Maybe I'm making this more difficult than it has to be. Windows are such a big expense that I don't want to get it wrong.
Sadly, Milgard closed it's Denver factory. Argon was once an option for the window I want.
It never occurred to me to have fixed windows be triple paned! That's an excellent suggestion that I will go with if I don't change the front picture window on the north side. That window is part of a bay window setup that does nothing for the house aesthetically or in terms of energy-efficiency. I'm thinking of replacing that with just a series of single hung windows. But you have me thinking now that fixed glass with smaller awning-on-top sections (triple glass for the fixed) might be something to consider there. First, my tired brain has to recover from figuring the south side.
Dot,
It is a row of narrow windows mounted up high. A good way to bring in natural light while keeping wall space free.
Splitting windows is a good way to get a bit of extra energy efficiency, it also means the operable windows are much lighter, which means much less flex if you go with vinyl.
Oh! I googled "clerestory windows" and saw photos. They are beautiful! I wish I had those in bath areas as opposed to skylights. Pigeons just poop all over the skylights. But I love those silly birds so I put up with it (and eventually/thankfully it rains). I wonder how hard it would be to take out the skylights and put in the clerestory windows as awning-type windows? Also, the skylight wells were badly made and are crooked and just generally look bad.
Hi Akos, I'm also considering a higher SHGC coating on south-facing clerestory windows (see https://www.greenbuildingadvisor.com/question/higher-shgc-glazing-for-marvin-or-andersen-windows) and curious about your lived experience with the clerestories.
What glazing and SHGC and U-Factor did you end up installing there?
You mentioned the cold winter nights - How about winter mornings and days?
I'm installing high south-facing clerestories over a yoga space that won't be used at night but I'd like it warm in the morning/day-time.
(I realize this is a bit off-topic on this thread and I'd appreciate your response in my other thread!)
Dot,
My impression is that your primary interest is in the aesthetics and comfort of highest possible VT and SHGC with a little less concern about U factor for your windows. Not that you are looking for poor performing products, but you have very specific wants that leaves U factor as third on your personal requirements list and as much natural light as possible as a big number 1.
I am curious why you I89 on your south facing windows versus LoE-180 when the VT and SHGC numbers are virtually identical between the two?
Greg,
Yes, you are correct that aesthetics are important to me, but energy efficiency is too. Not losing too quickly the solar gained during the day is important. The way the house is situated makes too much solar in the warm months not an issue, so I don't have to worry about that. There are so many tradeoffs to balance. I know that casement windows are the most energy efficient. However, I want screens on the outside to lessen bird hits, and I cannot seem to get inswing casements. But outside screens also prevent some solar gain. Will go with the tradeoff of a single-hung window with grid on the upper sash where there isn't an outside screen to hopefully prevent bird hits to the upper sash while still letting in more solar than the bottom screened sash.
But back to LoE, are you saying that there is no difference between I89 and LoE-180 for the south windows? I thought that the I89 would offer better light -- closer to full spectrum and more of it -- than the LoE-180 while still preventing rapid loss of heat from solar gain in the winter once the sun goes down. Did I figure that wrong?
Clear glass would be perfect for the warm months but would lose the solar too quickly in the colder months. In a perfect world, I would have interchangeable, seasonal sashes with the new German bird deterring glass. But, sadly, I also have to work with what actually exists and what is obtainable where I live.
Do you actually have a window manufacturer offering a window with only an i89 coating, rather than than standard use of i89, which is as an additional coating along with the LoE-180?
The difference in amount and color of light between the three options:
1. LoE-180 only
2. i89 only
3. LoE-180 + i89
is really tiny. The i89 only would have about 1% higher visible light and a very slightly better spectrum, but you'd have to do a very careful side-by-side inspection to notice that difference.
But that might all be a moot point: I'm not sure you can get option 2 in that list. Do you have a window manufacturer who is offering that option?
Charlie,
You may be right -- I responded late to your first reply. I'm waiting to hear back from the window company. So if it isn't offered on it's own, and considering the excellent information you provided about the tiny difference involved, I'm thinking LoE180 plus i89 for the north, and LoE180 on its own for the south since excessive solar is not an issue on the south for this home (which is unusually well-situated for passive solar gain in the winter).
How does that sound to you? Am I getting something else wrong (a possibility for sure)? Any advantage to only LoE180 all around, north and south?
I'm also replying to your post #20, above, that was your response to an earlier post of mine. Nested posts can be both a blessing and a curse at times :-)
I have never seen i89 alone, without any other LoE coating. Cardinal I'm sure could make such a thing, but I don't think they do. It would have to be a special order if they'd do it at all.
I don't think there is any reason to try for i89 alone anyway. LoE 180 is the least aggressive normal coating, and it doesn't have much in the way of negatives. If you went with LoE-180+i89 for all of your windows you'd probably be pretty happy with the results. The more aggressive coatings are mostly for additional SHGC improvement, but the cost is much reduced VT. If you aren't in an area with a need for the maximum SHGC, then the tradeoff for the more aggressive coatings isn't really worth it. In terms of just U value, the more aggressive coatings don't really gain you much compared to LoE-180. If you want higher U values, triple pane is a better option -- but then you can be limited in terms of frames and manufacturers. Triple pane windows get HEAVY.
Bill
Thanks, Bill! So my list of glass options now:
1. LoE 180 on all windows, or
2. LoE i89+LoE 180 on all windows, or
3. LoE 180 by itself on the south side with LoE 180+i89 on the north
After much waffling, I'm now leaning towards LoE 180 on all windows. The reason being that I think light would be compromised without great benefit with the combined LoE 180+i89. In other words, I think LoE 180 would get the job done with an acceptable balance between light quality/quantity and keeping the solar heat gain after dark in the cold months.
Thank you also for mentioning the weight issue with triple pane -- something to consider for sure. I'm not getting triple on the south side but will think about it carefully when it comes time to do the north side.
With a triple pane window, the extra weight from the third piece of glass puts extra stress on the frame and hardware. You need to be sure the windows are OK with that extra weight -- there have been reports of some frames that aren't really up to the task and bind. With a non-operable window there is much less to worry about.
If you're in an area that gets really cold in the winter, triple pane windows are very nice -- especially for any really large windows. You don't get that flowing cold draft off of a triple pane window on really cold nights.
Bill
Just saw a Cardinal LoE 179 mentioned in a technical bulletin. Is that something new? Not finding too much else about it. Will ask the window company about it as well, but, honestly, people on this website seem to know more about windows than the window company.
Also, are grids not appropriate for south side passive solar windows? Would they block too much sun if only on the top part of the window? As mentioned previously, I am considering those to help prevent bird hits. Single hung windows only have a screen on the bottom part of the window, so I felt there needs to be something to tell the birds a surface is there on the top part of the window. But I'm wondering if I should consider bird tape or dots or something like that which would not block as much light as grids.
LoE-179 is an obsolete coating, it was superceded by LoE-180.
So far as availability of i89 as a stand alone coating, Cardinal does offer Di89 as a stand-alone coating which is intended to "help more windows and doors meet the new Energy Rating of 34 throughout Canada. LoĒ-Di89 is a coating applied to the 3rd and 4th surface of a dual pane unit which allows more energy from the sun to enter the home while the low U-Factor keeps the heat in."
And as an alternative to LoE-180 and LoE-D189, Cardinal offers LoE-180ESC....'
"LoĒ-180ESC is an update of our successful LoE-180 glass and is designed to help meet the new performance requirements for ENERGY STAR® Canada in 2020.
It keeps homes warmer and more comfortable by blocking heat loss to the outside and letting the sun’s heat stream in. With a glass U-Factor of just 0.26 and an SHGC of 0.71, LoĒ-180ESC is the ideal product for passive solar applications in Canada."
Although these products are primarily targeted to the Canadian window market, they should also be available for the US market assuming that the window company chooses to offer the product as an option.
Comparisons:
LoE-180 on surface 3, LoE-180ESC, and Di89 all have a VT (Visible Light Transmittance of 79%, compared with 82% for clear glass dual pane.
LoE-180 on surface 3 has a SHGC of 69% while LoE-180ESC, and Di89 have a SHGC of 71% compared with 78% for dual pane clear glass.
All three coatings have a U-factor of .31 without argon compared with clear glass dual pane of .48 and a combination LoE-180 and i89 at U.24 without argon.
Also keep in mind that these are glass-only numbers. Window performance numbers are based on the entire window system, not just the glass, so that the numbers for entire window systems won't look as good as the glass-only numbers.
Yes grids will affect VT and SHGC performance numbers.
To protect against bird strikes you might want to look into "invisible" (to humans at least) films that you can apply to your windows. Test performance results that I have seen indicate that they seem to work quite well.
Grids are out, bird film (or tape or dots) are in. I think the film might void the window warranty, so probably bird tape in stripes or dots.
Yes, I discovered the number differences yesterday re: glass vs. finished windows when I embarrassed myself by telling the window salesman that the numbers were wrong on the window proposal.
Another LoE?! You have to be kidding me. So now there's LoE180ESC which if I understand correctly is new and improved LoE180 letting more light in? Well at least I don't have to consider 179. Small mercies.
So ESC and i89 outperform 180. But how do you compare them against each other when the differences are subtle to none? I might as well flip a coin. Am I missing something here? And there's still i89+180 (which probably compromises VT).
It's bad enough with window styles. One website says to get casements for superior energy efficiency. Another says don't get casements because the cranks will wear out and wind can take those windows right off your house. Again, It seems like I might as well flip a coin.
Dot
i89 is different from LoE-180, so it's not really correct to say one outperforms the other. Typical applicaitons would use those two coatings TOGETHER.
Remember that a typical custom home build is like building a prototype -- your home is unique, and has never been built before. This means EVERYTHING is custom. Manufacturers know this, and they make lots of options so that their products can fit into a near infinite number of potential home designs. This is both a blessing and a curse, since you can find great products for your build -- but you sometimes have to do a lot of work to FIND that perfect product.
Bill
Ok. Offering multiple options for custom builds sounds reasonable.
There is the possibility that i89 by itself is an option. If i89 were available on it's own, I could see advantages for the south side of the house. But would have to have some numbers to be sure. Waiting to hear back from the window dealer who is waiting to hear back from the window manufacturer (who is probably waiting to hear back from the glass manufacturer).
What fun would it be if it was easy? As it is, it's a challenge and who doesn't like challenges?
Seriously though, you may be over thinking your glass selection and maybe unnecessarily stressing yourself out as a result.
First ask the window company what they offer. They may or may not have all of these options available so that you can look at your options.
Second, you weren't far off when you asked if you might just flip a coin. Honestly the performance of the choices that you have been looking at are virtually identical and realistically any differences are so minute that you really won't notice variations between them in a real world application. You mentioned grids and adding or removing grids will likely make a bigger overall difference than choice of glass coating.
If I was adding windows and had all the options available I would consider LoE-180/i89 combo for the best U factor performance and very similar if not almost identical VT and SHGC performance versus the other selections.
LoE-180ESC would be my next choice, Di89 as third choice, and original LoE-180 as fourth choice for maximum VT and SHGC performance, but I wouldn't worry about any combination of the above choices or the possibility of tiny variations between them.
"And there's still i89+180 (which probably compromises VT)." Clear glass VT 82%, three options mentioned 79%. I can't find i89+180 VT on Cardinal web site, but I wouldn't expect worse that 78% in that configuration.
Fun? Hmm. That's not a word I would have used to describe my replacement window buying experience. I would agree that it's a challenge!
Yes, I agree about the overthinking. There was a window buying "mistake" in the past. Once bitten, twice shy as they say. I'm determined to be a fully-informed consumer this time and not miss anything.
Getting the i89/180 stats from Cardinal is something I need to do as well as the stats for i89 by itself if it is available by itself. So a couple pieces of the puzzle are missing, but it's coming together well overall.
It's really comforting to know that when you are dealing with these particular options, there isn't really a massive mistake to be made. When it comes to the glass, grids on the south side would have been the most significant error I could have made as you point out.
Does anything else vary with the LoE options we've been discussing? Tints? Iron vs. other metals/minerals? The devil may well be in the details. I saw a discussion about tints -- awful green tints or strange grey tints with LoE coatings, but I think that doesn't really apply to the ones I'm looking at. Pretty sure that was a problem with the more aggressive coatings. But thought I better ask here just in case.
366 has a green/gray tint to it. 180 doesn't really have any tint, but if you put it next to a clear piece of glass it will look "darker". The general rule is the more aggressive the coating, the more of a tint you're likely to have -- even if it's just neutral gray.
I'm not aware of the manufacturers publishing the exact chemical composition of any of their coatings. The coatings are so thin that there isn't going to be very much of anything in any of them though. The entire amount of materail in one of those coatings over the entire window is probably only a few grams at most.
I have posted a link before to Cardinal's technical document that has data on all of their coatings. You can probably find it in other LoE threads, otherwise post here and I can dig the link up and repost it again.
Bill
Thanks. That makes the tints clear (no pun intended).
I will go back and check the Cardinal link. I thought I went there and didn't find i89 info. (because it isn't available by itself?). The dealer told me that 180ESC is not available. Still waiting to hear on the availability of bird glass and i89 on it's own. I've got the figures for the combined 180/i89 for these windows. Don't know if I saw that as compared to clear glass -- but I will go back and check for that, too.
Bird window film would violate the warranty. But bird tape and dots would not.
Would you please give me your opinion on casements vs. single hung? Is there really that much of a difference in terms of energy efficiency? I'm a little worried that being high on a bluff where winds can be very strong that the windows might get ripped off their hinges. My first choice would be inswing casements, but sadly Milgard won't do that. A million options for window coatings but they can't give two casement options?
I would consider LoE-180 "by itself" before I'd try for i89 only. i89 is usually used as a supplemental coating, adding to an IGU that already has one of the other LoE coatings on it.
I've never used any bird films. You could try one of the flashers that spins in the wind. These are usually used to keep birds off of roofs, but I bet they'd work with windows too. They scare the birds so the birds stay away from them. If you want to go with a grid, keep in mind that many times those grids are removeable (unless they are installed between the panes of an IGU), so you could take them off if you end up not liking the look.
Casements are better than single hungs in terms of air sealing. Single and double hung windows aren't often installed new, they're most common in retrofits and renovations in areas where the goal is to preseve a historical look of an existing structure. I would never consider single or double hung windows for a new build myself.
If you're worried about the durability of casements, you could try a tild and turn, which has somewhat similar functionality but tend to be a lot more solidly build. Another possibility is an awning window, which is like a casement on it's side. In my own home, I have several large windows that have the upper 2/3 to 3/4 as a fixed window, and the lower 1/3 to 1/4 as an awning window. This is better than a single, large operable window in many ways.
Bill
Have to subscribe to this thread. Excellent discussion.
In response to comment #38, shiny bird repellers are out. I want the birds here, just not hitting the window. The more I read about it, I'm pretty sure bird tape will do the trick.
The mention of fixed windows with a smaller awning window is interesting. The window salesman suggested that. I rejected it outright because I thought windows should open as fully as possible everywhere not just in an egress. But how many people open their windows fully? I find that I don't (unless I've burned dinner -- and that's only the kitchen window). I have an awning window in the kitchen. In fact, it's the only one in the whole house. And it works remarkably well to vent air out for some reason I don't fully understand.
I'm almost afraid to mention this because it is so controversial, but the one advantage to i89 by itself on the south side is the LoE starting fires issue. There are those, including scientists, who believe LoE reflecting strong sun has been responsible for fires and melting siding. If the coating is on the interior pane, it does not seem to do this. And before everyone says this never happens, I actually experienced it with a large sunroom that was on the south side (it was removed a few years ago). The LoE in one spot was concentrating sun in such a way that it melted an intercom. And there was seal failure in certain windows that seemed to be because of sun being aimed at it from other windows. Having been fire evacuated during the worse fire in Colorado history to date, fire is no small concern. I've done a great deal of fire mitigation on the property and am working to get all wood off the exterior of the home. i89 on its own for the south side could be a reduction in fire risk.
I don't think that LoE180 will start fires either--anything that's high solar gain will be letting the solar heat in, not reflecting to to where a fire might start.
It's not the LoE coating that causes things to start on fire, it's the curvature of the glass that concentrates the energy at some point in the distance. The only thing a LoE coating MAY do is to slightly increase the total amount of energy reflected over a slightly wider range of angles compared to clear glass alone.
Part of my work is designing optical communication networks. We work with this stuff. There is a phenomenon known as "total internal reflection", and what it is is that at certain angles, ALL of the light is reflected (no losses from the reflecting surface). At certain angles, clear glass will reflect all the light coming in. The LoE coating forms what is known as a "thin film filter", and it will result in reflection of some additional wavelengths of light at other angles (compared to clear glass), which could result in a wider range of angles with higher energy content compared to reflections from clear glass alone. In NO CASE will the energy EVER exceed the total amount of energy coming in from the sun, period. All you can do is have the curvature of the glass focus that light coming in onto some point in the distance, and that concentration of energy caused by the focusing is where the heating is coming from.
In my own opinion, LoE's potential to increase risk here is near zero compared to the risk of clear glass alone. Since essentially ALL windows these days are LoE in some form, you don't really have a good control group to compare with where you can definitively say "LoE made x% increase in fire starts compared to clear glass". Who can really say that a clear glass window in the same place would not have done the exact same thing? Real data requires controlling all the variables, and I haven't seen anyone do any experiments like this.
I would not worry about LoE as a fire risk here. If you are concerned, just put up a window screen during fire season. Window screen typically says what it's open area is, and whatever isn't open reduces your reflection twice. What this means is that if you have an 80% open window screen, it reduces the sunlight coming in by 20%, then it reduces the reflection by another 20% on top of that. Assuming total reflection (no losses other than from the screen), this means (100% incoming sunlight * 0.8 open screen) = 80% reflected sunlight * 0.8 open screen = 64% reflected energy "getting out" to hit anything else. You're dropping a bit over 1/3 of your total sunlight energy with that 80% open window screen. That screen will work on any type of loE coated glass, glear glass, or even on a mirror if you hang the screen in front of the mirror. I'd do that before I'd rule out LoE coatings in general due to a remote possibility of them focusing sunlight over a small percentage more angles compared to clear glass.
Bill
Thank you Charlie and Bill! That's very reassuring.
Bill, will an inside screen help diminish any reflection at all? I'm pretty sure the answer is no, but I have to ask because Milgard won't give me inswing casements (my top choice of window type). So the screens will be on the inside. Since Ornalux bird glass is another thing I can't have, I will put bird tape on the outside of the windows (leaves small dots or stripes that help birds recognize there's a surface there). Hope that will cut down on reflective problems, too.
It makes sense about the curvature of the windows and lowE problems. My sunroom that had those areas of high reflectivity (and an intercom melted) had curved glass -- very cool in the 80's (think Wendy's restaurants).
So I've chosen Milgard fiberglass casements (with bird tape I will add), drywall returns / no added sills inside / stucco surrounds outside (no trim in or out), one awning window in the kitchen. Will be having two very badly built, pain-in-the-backside skylight wells and the skylights removed and high-up rectangular windows put in where three bath areas will be (or are now) too dark.
The only thing I'm still kind of unclear on (and am waiting for a little more information from the dealer) is why would I want to combine i89 with 180 on the south side? That seems like overkill to me and risks haze without any real benefit. I'm not even sold on the i89 / lowE 180 combo for the north side.
So that's where I'm at. Hope to wrap up the order this week for the south side even if I have to flip a coin! Have to say I'm real disappointed in the window industry that bird glass isn't standard and inswing casements are not an option.
And something I still wonder, and may never find out, if getting clear glass then adding film on the interior or exterior would be better than factory lowE on the south side. Have a feeling the optics would not be as good but certainly the reflection would not be such an issue. Just seems impractical to film so many, mostly-large windows. But, as Bill and Charlie have stated, the reflectivity is probably not an issue anyway.
A screen on the inside will do nothing to reduce reflections on the exterior since it won't be in the path of the light. You could potentially make your own screens though, and for this application you don't even need a frame -- you could just tape the screen up during fire season. Use the flexible fiberglass screen (not aluminum) for this, since it will be easy to work with and won't scratch the glass. The screen will also provide a sort of safety net for birds -- something squishy to fly into instead of the hard glass. My guess is the birds will see the screen though and steer clear.
I've had good luck with Velux skylights. If you can use some of their standard sizes, they aren't even all that expensive. I always use their laminated glass skylights though regardless of where they are (code requires their use in some locations), since the laminated glass reduces the sound of rain.
I don't think there is any increase in haze with the LoE-180 and i89 combination. If you wanted to skip the i89 coating you could, but that would reduce your wintertime thermal performance of those windows.
You'll NEVER get as a good of a coating with window film as the factories do with the LoE coatings. You'll never even get close. LoE coatings are applied in very clean enviornments under very controlled conditions. This means near perfect coatings without visible defects. Window film almost always will have some bubbles, will peel a bit, and tends not to age well.
BTW, regarding the bird avoidance stuff. My dad is a big bird watcher and uses stick-on bird visibility "stickers" that are sort of translucent. They supposedly reflect IR light that the birds can see, so the birds see them "floating" in the glass and know there is something there. Over time, some of these turn slightly to goo and mess the window up. I've used acetone to clean off the goo to get the glass in good shape again. That might be a trick to remember if you're also going to be using bird visibility things on your own windows.
Bill
Bill,
The casements open to the exterior, so they would hit any screen on the outside. Wouldn't be able to open the windows during fire season. The winds can be awful on the bluff where my house is. Anything taped would be Gone With the Wind.
The skylights I have are crank-open Velux brand. The problem is the badly-framed, wonky way the skylight wells were built. They look awful. And as you look up to a skylight itself, even it sits wonky because of the badly built well. They add nothing to my life. Skylights are an energy waster (40% more than a regular window). And there's nothing like pigeon poo sitting there for weeks in the dry season in between rains. No thank you. They are going. That decision was an easy one. Even the high cost of adding those windows at the top of the back walls of those bath areas (which is the south wall by the way) is worth it to me to get a regular ceiling back.
Ok, losing wintertime thermal performance may make having the i89 / lowE180 combo worth it for the north side. But I'd lose solar gain on the south so really any loss would be cancelled out by the gain without i89 (and reverse with i89). It's so close, that I would really have to see the numbers side by side, and I'm still waiting for that from the dealer.
Thank you for clearing up once and for all the window film musings floating around in my head. Done wasting mental energy on that one.
Your dad is a good man! Who doesn't love a guy who loves birds! I've got translucent stickers on my windows now. Sort of hate them. Too decorative -- butterflies, hummingbirds, leaves, etc. They do make the coolest patterns on the walls though at certain times of the day. But I'm a minimalist at heart, and anything decorative annoys me. The dots will do. Window industry if you are reading this conversation -- make bird glass standard!! The time has come. And also give us inswing casements already. Europeans have them. Not fair.
You may be able to find a better way to fasten the screen. With a casement, you could wrap it around the edge a bit when the window was open, then close the window to trap it. Another option would be some of the super duty velco stuff. The stuff they give you to attach EZPass tags to windshields would work. I'm not sure if E470 has tags like that now or if they're still doing bill by plate with the camera system. The beefy stuff the EZPass people use is a sort of tape with what look like lots of little mushrooms that lock into each other when pressed together. It holds really well, and it lasts (9 years now for my EZPass tag). That might be another option for you. If it's too much trouble, I wouldn't worry about it. I really don't think LoE is any risk.
My guess is the "energy loss versus solar gain" difference is pretty minimal, but I've never tried running numbers. My first thought is that you might be able to negotiate a better price if all your windows are the same. I don't really think any small <10-15% performance difference for a small number of windows is going to be a big deal overall though.
Humingbirds (I have them at my house too), always seem to be able to avoid the glass. I think their "swoop and hover" style of flying probably gives them some time to stop and reflect (no pun intended) about the wisdom of continuing to fly towards a window before they hit it. It's smaller birds that tend to dart long distance that we've seen hit before, things like sparrows and the ocassional blue jay. Most of the time they get stunned, and they're OK after a rest (probably thinking "AHH! WHAT WAS THAT!!!"). I have seen a few not make it though. They do still hit with the stickers, but it seems less frequent.
The most memorable bird and window moment I had was when a hawk was after a chipmunk under the bird feeder. The hawk dived at the chip munk and brushed the window with a wingtip. The hawk was fine, the chip munk was dinner, and it was interesting to watch. I think that particular hawk keeps an eye on that bird feeder. Squirrels like to frequent it too, and we came home once to see some bloody goo on the feeder. I think the hawk got a squirrel off of the side of the feeder. Paraphrasing Shakespear a bit, I remarked "ahh, to get food or to BE food, that is the question" :-)
Bill
I've discovered that crows are body guards for smaller birds. I've been adding corn to the seed mix and throwing it on the ground. If you have crows around, the hawks stay away. I rarely have hummingbirds even though I planted flowers that are specifically to attract them. But I have the translucent decals that are in the shape of a hummingbird so maybe they don't like those.
I'm totally in agreement about the energy difference being too minimal to worry about. I will wait for the dealer to get me those numbers out of curiosity, but I'm not worried about making the wrong decision anymore. Almost certain I will go with the combo i89 / lowE180 on the north only if I do it at all.
This has been REALLY hard! I'm very grateful for everybody's help in this discussion. And everybody WAS helpful -- there was not a single unhelpful comment. This is a marvelous website for people struggling with their houses and wanting to do things in as an environmentally-responsible way as possible.
Will definitely post for help with the north side when I get there -- only have a couple issues to grapple with there. But they are a bit of a puzzle (not lowE related).
So I have the numbers now for lowE180 over clear and lowE180 over i89 on 4th surface. Anyone have an opinion on having / not having the second coating on south-side glass? The window dealer assures me there is no visual compromise / no haze. I'm not convinced of that. On the Cardinal website, their lowE180 is called "Passive Solar Control Glass." There is no recommendation along with that about adding i89 for even greater solar control / energy benefit.
Here are the numbers for one window:
1/8" Cardinal 180 (Low-E) over 1/8" 4th Surface HP Coating with Gray EdgeGardMAX spacer
U-Factor: .29
SHGC: .46
VT: .57
1/8" Cardinal 180 (Low-E) over 1/8" Clear with Gray EdgeGardMAX spacer
U-Factor: .34
SHGC: .48
VT: .58
Thanks in advance for any information on choosing between these two options. I know that condensation can be an issue with i89. That concerns me a bit now that I know it has little to do with indoor humidity and more to do with weather. We do get a good deal of snow in the winter even though it's an arid climate zone here. And I intend to have minimal window treatments which I would hate to have affected by water. Oh -- and I'm going to have drywall returns and sills and would REALLY hate to have all that expensive work getting dripped on even though it will have a high-quality satin paint.
You'll never notice a 1% different in VT (Visual Transmission) between the two options. Even with the two different windows right next to each other you're not going to be able to see such a small difference.
The 2% difference in SHGC isn't going to make much difference in practice either.
The 5% U factor difference is most significant, although still fairly small. If the cost difference isn't much, I'd say this 5% difference is worth it here.
The condensation issue is because i89 reflects "heat" (IR radiation) back into the room, which results in the glass pane being SLIGHTLY cooler than it would otherwise be without the i89 coating. Condensation occurs when a surface drops below the dew point of the air around it, so a slightly cooler pane of glass will start to show condensation a little bit sooner (in terms of temperatures), all else being equal. With your very low humidity levels, you probably don't really have anything to worry about.
Bill
A couple thoughts on your previous comments.
"The window dealer assures me there is no visual compromise / no haze. I'm not convinced of that."
The window dealer is correct. LoE-180 and i89 are virtually as color-neutral and haze-free as clear glass.
"I know that condensation can be an issue with i89. That concerns me a bit now that I know it has little to do with indoor humidity and more to do with weather."
I am a bit puzzled by your comment here since window condensation is all about your indoor humidity level and how it interacts with the dew point temperature of the glass.
Obviously the outside temperature matters because your glass temperature is directly related to how hot or how cold it is outside, but indoor humidity level dictates whether or not you have wet window glass.
Uh oh. It looks like I misunderstood a previous comment about condensation. My indoor humidity is VERY low -- no humidifier on the furnace, dry climate, etc.
IF humidity / condensation is NOT an issue, and IF visual quality is NOT affected by the addition of i89 glass coating, is there still any reason to have the i89 on the south side (or not have it)? It seems to me it's a gain-a-little / lose-a-little situation either way you go. So your U-factor is a little better, but you drop your light and solar gain a little. I'm just not seeing the point of the i89 in a passive solar situation for the sunny side.
And how do window coverings and i89 work together? If the coating is on the inside glass, and you have curtains (I have thermal sheers) closed after the sun goes down. How is heat being kept in by the i89 coating if there is fabric between the warm air on the inside and the glass?
A house designed for passive solar still has heat loss through the window 12h per day at night, this means that you'll generally loose less energy by having a low U factor than a high SHGC.
I would look at figure 22-1 here:
https://www.cardinalcorp.com/source/pdf/Technical_Glass_Guide_Web.pdf
If your indoor RH is bellow the values shown for your local winter time outdoor temperatures, than there is absolutely no reason not to go with i89 on surface 4.
One thing to watch with interior coating is cleaning the windows with a razor blade (ie. after painting or staining trim) as the coating can be scratched.
"The coating can be scratched." Something to think about for sure!