Can someone help eplain low-e?
I am looking at Andersen 200 series windows.
I was told at HD that the low-e is on both of pieces of glass and this will reflect heat from the sun back outdoors and heat in my home back indoors in the winter months.
At my local lumber yard I am told it is only on one peice. The lumber yard said the low-e will only reflect heat from the sun back outdoors and will not reflect heat back indoors in the winter months.
If the lumber yard is correct why should I spend the extra money for low-e on north facing windows?
Replies
Read this
http://www.efficientwindows.org/lowe.cfm
http://www.arkema-inc.com/index.cfm?pag=84
Suprisingly enough, both HD and your lumberyard are incorrect.
Oh Mr. Sledge hammer (tongue in cheek), could you please elaborate for us so we may bathe in your brilliance?.
Edited 5/12/2008 7:52 am ET by jocobe
True, but HD was closer than the lumber yard to getting it right.
And why would it be a surprise that HD got it wrong? (and tongue firmly in cheek of course)
Edited 5/13/2008 7:56 pm ET by Oberon
Edited 5/13/2008 9:28 pm ET by Oberon
Not sure which is correct but I do believe that the low-E coating is standard glazing in Andersen windows (at least it is on the 400 series), so if you're getting Andersens, it't not even an option (you'll get it whether you want it or not). I could be wrong since you are talking about 200 series.
C Miltier,
1. Typically, a low-e double-glazed window has one low-e coating. Some triple-glazed windows have two low-e coatings.
2. The low-e coating changes the emissivity of one surface in the window assembly. This has a measurable effect on the window's R-value. Low-e windows have a higher R-value (that is, a lower U-factor) than similar windows without the low-e coating.
3. The effect of the higher R-value (lower U-factor) is useful in both summer and winter. During the winter, a low-e window helps keep heat in the house. During the summer, a low-e window helps keep heat outdoors where it belongs.
4. Spectrally selective coatings on some windows affect the window's solar heat gain coefficient (SHGC). Windows with a high SHGC allow more solar gain than windows with a low SHGC. In general, windows in Georgia should have a low SHGC, while windows in Vermont should have a high SHGC.
5. It is possible to buy low-e windows that are either high-SHGC or low-SHGC. Unfortunately for those of us who live up north, however, low-e windows that are high-SHGC are rarely stocked. Canadian window manufacturers are more likely to have them than U.S. window manufacturers.
low-e for dummies ..
a light coating of silver on the inside of the glass, like a bad mirror, reflects some of the UV back outside .. so clear that manufacturers often assemble the glass, low-e side out, window gets progressively darkers as sliver oxidizes ..
Huh?
So over years, will a low E window be darker -- less light/view coming in?
Again, not addressed to me, but the answer is that LowE coatings don't darken.
Some hardcoats may have a slight color shift over the years (gray/blue in some cases), but a softcoat won't noticeably change color or darken at all.
Very helpful post. How do you figure out whether yr manufacturer's coat is hard or softcoat? And what do the 240 or 270 degree notations mean?
Cardinal Glass produces most of the LowE coatings used in residential windows in North America.
The designations 240 and 270 relate to two different Cardinal coatings LoE2-270 and LoE2-240. Technically they should be LoE squared, not "LoE2" - 270 and 240, but I am not sure the site allows superscripting - and if it does I have no idea how to do it here...
Anyway, the first number in Cardinal's nomenclature refers to the number of layers of silver in the coating and the second and third numbers are the Visible Transmittance of the glass/coating combination.
So, LoE2-240 (again squared, not 2), has 2 layers of silver and a VT of 40%. The LoE2-270 has two layers of silver and 70% VT.
A couple of other ones are LoE178, which has one layer of silver (HSHG coating), and 78% VT, and LoE3-366 has three layers of silver in the coating and a 66% VT.
Edited 5/13/2008 9:06 pm ET by Oberon
And They are softcoats?
Yep, Cardinal only produces softcoats.
Other softcoats would include PPG's Solarban60 (two silver layer coating) and Solarban70XL, their three-layers-of-silver coating.
PPG also offers Sungate 100 and Sungate 500, these are hardcoats.
Guardian offers their softcoat - ClimaGuard LowE - a dual-silver coating; and about six different versions are available (with various performance levels), of their SunGuard product. And if memory serves (I am doing this off the top-of-my-head, so no guaranties that I am 100% accurate with all the different product names), SunGuard is primarily commercial while ClimaGuard is primarily residential.
Guardian also offers hardcoat coatings - and AFG offers hardcoat and softcoat products as well.
What is interesting about AFG's offerings is that they use titanium rather than silver in their softcoat LowE coatings, such as their Comfort Ti-Ac line of coatings.
Edited 5/13/2008 9:26 pm ET by Oberon
To add to what Jon said about alt codes here is a web site that has a list. Scroll down past the first screen of bs... Note that when using these alt codes, you have to use the number pad on the right of your keyboard, which may require that you hit the "number lock" button also on the right side of a standard keyboard. You can't use the number keys along the top part of the alpha-numeric part of your keyboard. This stuff will be different on most laptops since they have different keyboard layouts.
Matt thanks!
That one is now in my favorites folder!
keypad! I was using the lowercase on the "regular" keys! DOH!!!!!
okay - LoE²-272, LoE³-366 -
thanks again Matt and Jon!
Edited 5/14/2008 7:21 am ET by Oberon
I was just looking at the Anderson web site. They said they use Low-E4 glass - wonder what that is...
And, yea, using the wrong part of the keyboard only took me a year or so to figure out... :-)
Edited 5/14/2008 7:22 am ET by Matt
Low-E4 glass includes, as standard, an easy-clean (some say self-cleaning) coating on the exterior lite surface, as well as a factory applied clear plastic film on both the interior and exterior exposed surfaces to protect the glass during manufacture and construction, and a LoE² coating, and argon fill.
a more basic q... above and elsewhere I saw references to the #2, #3 surface, etc... I can guess what that means but can you please briefly explain it?
Glass surfaces are counted from the exterior starting with #1.
So surface #2 is the inner side of the exterior lite and surface #3 is the interior side of the interior lite.
Surface #4 is the surface that someone actually touches inside the home.
My comment is not really germane to this discussion, but you mentioned not knowing how to do the "²" symbol so I'm posting to feel like I have something worthwhile to contribute.ALT + 0178 will give you the ²The following key entries (numbers in the left column), when preceded by the "ALT" key will give you the symbols in the right column:
0153 (tm)
0167 §
0176 °
0177 ±
0178 ²
0179 ³
Jon Blakemore RappahannockINC.com Fredericksburg, VA
Thanks Jon,
That's really good information, unfortunately I am apparently missing something since I can't seem to make it work for me.
I have tried holding the alt key while typing the numbers and I have tried pressing the alt key before typing the numbers; but I have been unable to get anything out of it.
When I hold the alt key down and type, I get nothing. When I press the alt key prior to pressing the "0178", I get "178" (no zero) but nothing else.
Now I am going to be playing with this all morning until I get it figured out....
The same thing happened to me. I'm using Mozilla and a lot of the html stuff won't work with it. Bob's next test date: 12/10/07
Okay...I'll try it: again: edit: capslock on: NOTHING. Bob's next test date: 12/10/07
Edited 5/17/2008 10:29 pm by Jim_Allen
Use the keypad on the right side of the keyboard.
Jon Blakemore RappahannockINC.com Fredericksburg, VA
Anyway, the first number in Cardinal's nomenclature refers to the number of layers of silver in the coating and the second and third numbers are the Visible Transmittance of the glass/coating combination.
So, LoE2-240 (again squared, not 2), has 2 layers of silver and a VT of 40%. The LoE2-270 has two layers of silver and 70% VT.
Can you explain what the VT numbers translate to as to appearance?
40% seems like you'd be looking through dark glasses?
70% still seems like it would still be fairly dark.
While it is obvious there is a small darkening looking out, doesn't look to be that high a %?
Joe H
There are tinted LoE coatings that are designed for maximum light blocking while still allowing the folks who have them to see outside. These types of coatings are excellent on the windows on the western side of a home or other building to moderate the intense glare of the sun as it sets. LoE²-240 is an example of such a coating.
A single lite of 1/8" or double strength glass has a VT of about 93% or .93. There are slight variations depending on who made it and the exact formula used in the batch, but .93 is consistent.
Add a second lite in an IG configuration and the VT drops to about .87. Add a third lite (clear triple pane) and VT thru the three lites of clear glass is about .80. Add a fourth lite (for illustration) and you have a VT of .74.
The coating designations that you mention are based on the combination of two clear lites and the coating. So, a LoE²-272 coating will be about the same as looking thru four lites of 1/8" clear glass.
Looking outside thru the windows of a home, very few people will notice the difference between a 90% VT and a 70% VT. Very few people can tell that there is a LowE coating on a window. Your eye will see the difference between coated and uncoated glass in a side-by-side comparison, but not when there is no direct comparison.
Also, when purchasing a window, the VT given for that window includes the entire window in the calculation, including the sash and frame and any muntin bars or grills.
So, a 30" x 48" window with a 70% VT LowE coated glass, a thin sash/frame, and no muntin bars can very possibly have a higher overall VT than a 30" x 48" clear glasswindow with an 87% VT, and a wider frame/sash combination and muntin bars since the sash and frame and muntin bars pass zero light. Meaning that the coated window in this scenario actually allows MORE visible light into the home than does the clear glass window of the same size.
These types of coatings are excellent on the windows on the western side of a home or other building to moderate the intense glare of the sun as it sets. LoE²-240 is an example of such a coating.
Is this coating also a low heat gain?
Or would I need another layer?
What am I looking for in SE New Mexico, elevation 6800'? Lots of sunshine, great view south and west? I'm more concerned with heat gain in the summer than keeping warm in the winter.
Joe H
Joe H
One of the reasons that the coating manufacturers "invented" triple silver coatings such as LoE³-366 from Cardinal and Solarban 70XL from PPG, or in the case of AFG, triple titanium coating, was for lowered solar heat gain with better visible light transmittance than either tinted LowE coatings or tinted glass.
LoE²-240 is a low solar heat gain coating that also is helpful blocking glare because of the tinting. This is not a coating on tinted glass, which is also available from several manufacturers, rather this is a tinited LowE.
The triple silver (and titanium) products have the same or similar solar heat blocking ability of the tinted LowE coatings and tinted coated glass with better VT numbers. Cardinal coating numbers are so easy to decipher - first number = layers of silver, next two numbers = the VT - compare with Solarban products, for example, where Solarban 60 has higher VT than Solarban 70XL - so you must either memorize the numbers or else keep a cheat sheet handy!
Anyway, 70XL has a VT of 64% and a Solar Heat Gain Coefficient (SHGC - or how much heat passes thru the glass - lower number is better for blocking heat) of .27 when using low-iron glass, which is the standard for this coating. 70XL is available on tinted glass, directly from PPG, and using tints can lower the SHGC down to the .24 range or so depending on the tint used.
366 has a VT of 66% and a SHGC of .26 while a tinted coating like 240 which has a VT of 40% and SHGC of .24. So, the coatings have very similar solar heat blocking ability but significantly different light transmittance.
Thanks, I know the 366 coating is available on Jeld-Wen, don't know what other window manufacturers are available in the area yet.
Guess I'll find out when I build, escrow closes today.
Thanks for all the info, Joe H
What am I looking for in SE New Mexico, elevation 6800'? Lots of sunshine, great view south and west? I'm more concerned with heat gain in the summer than keeping warm in the winter.
What you probably need are overhangs.
Would need some climate info, and a specific solar incidence, but enough overhang to 100% shade the windows 80% of daylight hours for the six hottest months of the year is probably the sort of thing the calculations would suggest.
Here in my part of Central Texas that winds up being wrap-around porches, 6' to south, 5' E & W, at least 4' to north (here at 29ºN, the sun sets & rises ±30º north of due East and due West, adding a lot of insolation gain to the north wall in summer).Occupational hazard of my occupation not being around (sorry Bubba)
Oberon,Thanks. Nice read.How about a long article in FHB.KK
Some time back I posed this question and wasn't able to get an answer, so I will engage in a mild highjack here and ask you. When I submitted my site plan to build in the Columbia Gorge Scenic Area, one of the notes for approval indicated that a 14% reflectance was required on all windows facing areas where they could be seen from viewing areas in the Columbia Gorge. I have searched the Internet and could find reflectance values given for only a single brand of window film; none for windows. Searching the NFRC website turned up a document that gaves tolerances for various window parameters, including reflectance, but no real useful information. Do window manufacturers give reflectance figures for windows? How does one typically find out what the values are. What are the typical values for windows. What is done to change the reflectance. I would appreciate any insight that you can give on this.Thanks, Casey R
Hi Casey,
I remember your question and I thought that I had replied...
Memory - I remember that I used to have one.
Anyway, I am trying to remember if you needed to stay above or below that 14% range. I can't imagine wanting hight reflectance, so I am going to assume for this answer that lower reflectance is better.
Clear LowE (softcoat) coated glass on surface 2 of an IG is going to have reflectance in the 10% range or so. Using a tinted LowE or applying LowE to tinted glass or changing the coating to surface 3 will also change the reflectance values of the IG.
That change can be up or down depending on the coating, the tint, and the location of the coating, but as a guideline (off-the-top-of-my-head) any softcoat LowE on clear glass is going to be below 14%.
Sorry not more detailed, but there is a huge range depending on product, and I would also need to look up the specific products as well.
Your best course might be to contact the window company directly and then they can get the numbers from the glass / coating manufacturer assuming that they don't already have those figures.
Edited 5/15/2008 7:26 am ET by Oberon
Thank you. I looked up the post where I specifically asked the question and there was no response such as you gave. However, that is not to say I might not have asked the question in a different context to which you responded. The requirement regarding the 14% reflectance was worded such that it seemed that they were stating exactly 14% was needed. However, there were a number of other requirements which makes me think that they may not have said exactly what they meant. What would be good would be to find a list of reflectances for various windows so that I narrow down my search and select some candidate windows without having to write to all the possible manufacturers requesting their reflectance numbers. It appears that such information is not generally available, however.
You might try Googling individual companies and checking to see what they have on the ir websites.
PPG has a lot of that sort of information on theirs as I recall, but I am not sure if anyone else includes reflectance figures. TYpically because it just isn't something that most folks ask about.
Cardinal has a plant in Hood River, it might be worth while giving them a call?
As I indicated, I have looked at a number of window manufacturer's sites and found nothing about reflectance. A number of such sites will give various other window parameters, but reflectance is not one of them. I just tried to look at at the Cardinal site you mentioned and it locked up my computer so that I had to reboot. I will try it again later. Since I am too deaf to use the phone, calling doesn't do me much good. I will probably try emailing a few places, but such email, I find, usually gets ignored. Pella has a large facility in Gresham, which used to be Viking. I go by it often, so I might stop in. I think it used to only do vinyl, but I don't know the current product mix. Anyway, thanks.
CaseyR,
Try this one -
http://corporateportal.ppg.com/NR/rdonlyres/3DBFF6B2-E070-481E-8CBF-9A19A2AF6A79/0/CLPData.pdf
While it is specific to PPG products, it should help in getting you started.
Again, since there is a Cardinal plant not far from where you are building, I would strongly recommend that you stop in and see what they can do to help you as well.
While you can't buy from them directly, they could still be a resource to help you in your search.
Can an amateur, or even a pro like yourself, tell whether a window has low-e glass just by looking at it? My low-e windows don't have any tint to them but I paid the builder for low-e and the factory labels showed that some of them are low-e. I wasn't able to look at the label on every window.
I'm curious as to whether my sidelight windows and the the transom windows are low-e, which is the reason for my question.
I
Hold a flame near the glass and you will see four reflections. One for every surface of glass on the insulated unit. If you have LOW-E film, one of the flames will be a different color..View Image
What jocobe said...the center flame with the odd-color will show if you have a LowE coating.
You can also tell which surface has the coating depending on whether the odd color flame is closer to you or away from you. Closer flame will tell you surface 3 and further flame indicates surface 2.
Edited 5/20/2008 9:16 pm ET by Oberon
Good answer.
Are you aware of "Hard Low-E" and "Soft Low-E" and the difference?Spheramid Enterprises Architectural Woodworks
Click here for access to practice clicking
This wasn't addressed to me, but since I was lurking, I hope that Martinholladay doesn't mind if I sneak in...
There are two primary types of window coatings available - pyrolitic or hard coat - and soft or sputter coat.Softcoats are multi-layered coatings consisting of several different metallic oxides with silver as the primary heat-blocking ingredient. Softcoats are applied in vacuum chambers to finished glass.Hardcoats or pyrolitic coatings are applied to the glass while the glass is still semi-molten in the tin bath portion of the float process. Basically, the bottom side of the glass will have a coating of tin from floating in the bath (as does all float glass), but the topside will also have the layer of (primarily) tin oxide - which is the LowE coating.So in one sense, glass with a pyrolitic coating has two "tin-sides", but one - the LowE side - of them is much thicker than the other. Often, the pyrolitic coating is applied to the #3 surface of an IG unit if the unit is intended for use in a heating-dominated climate - but not always since there are also solar-reflective pyrolitic LowE coatings that are applied to the #1 or #2 surface of an IG unit to reflect solar heat gain in cooling dominated climates.Sputter LowE coatings are also applied to the air-side of the glass, primarily because sputter coats adhere better to the air-side, but also it is possible for the slight metallic (tin) layer on the tin-side to affect the performance of the coating.A sputter coat is applied in multiple layers, typically about 7 to 11 layers depending on the coating. People really don't realize, or can appreciate, how thin a typical sputter LowE coating is. Sputter coat folks measure the thickness of each metal oxide layer, as well as the finished coating, by how many atoms thick it is. A typical softcoat LowE coating is somewhere in the neighborhood of 500 to 1000 ATOMS thick.<!----><!----><!---->
Dual or (newer) triple silver sputter coats (low solar heat gain products) are generally applied to surface #2 of an IG unit, while single silver (high solar heat gain) is often applied to surface #3. <!----><!---->
<!----> <!---->
In a heating dominated climate, the two reasons for placing the LowE coating on the #3 surface of the IGU is to allow for solar heat gain in the winter and to block the transference of the heat from inside the home to the outside.<!----><!---->
<!----> <!---->
High Solar Heat Gain (or HSHG) coatings and Low Solar Heat Gain (or LSHG) coatings are all designed to block far - or longwave - infrared energy. This is the range that includes typical "household-produced" heat. This is also the frequency range of heat that is produced when the sun warms an object – the heat you feel reflecting from a hot wall or sidewalk on a hot, sunny summer day. While direct solar energy is shortwave IR, the heat released by a sun-warmed object is longwave IR…and hopefully that made sense. A typical hardcoat or single-silver layer softcoat works in this application since all types of LowE coatings block the far infrared energy - thus keeping winter heat indoors - but neither is designed to be effective at blocking shortwave infrared - thus "allowing" solar heat access to the home - winter or summer. Placing a high solar gain coating on surface #3 maximizes the level of solar heat gain thru the IG unit which can be an advantage in winter and can also be a disadvantage in summer. A Low Solar Heat Gain product, on the other hand, is designed to block both near and far infrared energy. It will keep heat - including direct solar gain – from passing thru the window in both summer and winter. <!----><!---->
These coatings are placed on surface #2 to maximize effectiveness against direct solar gain by blocking solar heat before it can pass into the airspace in the IG unit – and into the home.<!----><!---->
Edited 5/13/2008 8:37 pm ET by Oberon
Thank You, that has been a nagging issue of mine, when dealing with the glazing supplier I use. I am restoring single pane units, and I also need tempered for such, with LOW E.
These terms were not clear to me, until now, in reference to hard and soft.Spheramid Enterprises Architectural Woodworks
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Single pane tempered with LowE?
In that case you must use a hardcoat since the softcoat cannot be exposed - hardcoats are durable when exposed they do fine. Softcoats are fragile and must be protected (i.e. inside the IG).
If you are restoring using dual pane tempered windows, then you can use either coating.
No, I am trying to figure out, reading the spec book from new windows I plan to order (for a new house -- Kolbe & Kolbe) whether the coat is hard or soft. I was disturbed by how grey the sample window was, in showroom... its double pane. PS: I'm butting in too, Im not the restorer of old house.
Showroom samples always look very dark. It is much less noticeable when installed in the home.
Kolbe uses Cardinal coatings, and Cardinal does not offer a hard coat.
You are an amazing font of information. 1) How do you know so much and 2) am I well advised to buy Kolbe windows?
1) It really is my day job, not coatings specifically, but glass and windows quality, certifications, testing, product development...etc.
2) Because of what I do, I am exposed to propriatary information about many different glass and window companies. Because of the "insider" knowledge, I make it a point to avoid discussions of specific window brands and companies and I never compare different window brands either on line or off.
Sorry, but it avoids a very real potential for conflict of interest.
Because of the "insider" knowledge, I make it a point to avoid discussions of specific window brands
Reading through this thread and about to ask you about Jeld-Wen LowE 366 low solar gain coating.
Guess I shudda asked before I finished the thread?
Joe H
Joe,
I do discuss performance in generic terms, I just avoid being really specific about one company versus another or really specific about a particular company or overall performance other than what information might be readily available elsewhere - like I might comment on a website claim, for example. If that makes sense.
Oh, understood. Thanks again, you "cleared" some things up for me, so to speak =;-)
You are welcome. Believe me, I have learned so much about so much from reading on Breaktime about how the pro's do things that it is truly a pleasure to be able to offer something in return!
Speaking of your day job. A while back you were involved in the thread about a new window technology , riversong and and others were involved. Any late breaking news or newer results on it??
They can't get your Goat if you don't tell them where it is hidden.
As I recall that was the question of window glass that actually produced heat - windows as radiant heaters.
If that is the right discussion, then I still think that it is really interesting technology that has been available in parts of Northern Europe for awhile but is fairly new to our part of the world.
It is supposed to work as advertised, at least according to the European folks who have used them for awhile and according to the website of the folks trying to market their idea over here.
I would love to play with one of those windows sometime, but at this point it is still too much of a curiousity or nitch product in our part of the world, that may or may not ever become mainstream, so that I don't anticipate the opportunity to do so anytime soon, if ever. A shame, because it seems like a really interesting idea.
Thats the stuff. Thanks for the reply.
They can't get your Goat if you don't tell them where it is hidden.
Okay...so whats the best window? I won't tell anyone that you told us. Honest injun.... Bob's next test date: 12/10/07
Often it depends on what you are looking for.
There are times when I see people bashing a window that I really happen to like and there are times when I see people praising a window that I think is basically junk, and it is often very difficult to avoid commenting in either of those cases.
But I stay away from those discussions because I don't think that it would be appropriate for me to comment.
It seems that in cold climates, that Low E2 178 would be better choice because it has a higher SHGC = 0.63, U=0.30 , Where as Low E2 270/272 has a similar U value, but a much lower SHGC = 0.37/0.41
Is this correct?
Most manufacturers have Low E2 240 and 270 or 272, but I can't seem to find any using Low E2 178. Is it readily available? What manufacturers?
Good morning.
There is a very interesting debate between the proponents of high solar heat gain LowE coatings versus the proponents of low solar heat gain coatings (for use in heating dominated climates) in the glass / window industry.
This debate has been ongoing for a number of years with the proponents of HSHG (high solar heat gain) coatings saying that coatings that allow significant solar heat gain in winter are superior in heating climates because they allow free heat into the home when it is needed and the winter energy gains outweigh summer energy loss because of high solar heat gain.
The folks that promote LSHG coatings argue that the lower (improved) U-factor with these coatings (as compared with HSHG coatings) plus the advantage during summer heating season results in better year-around performance.
If one were to visit the Efficient Windows Collaborative (EWC) website http://www.efficientwindows.org/selection.cfm which is hosted and maintained by the Regents of the University of Minnesota, Twin Cities Campus, College of Design, Center for Sustainable Building Research and was developed jointly by the Center for Sustainable Building Research, Alliance to Save Energy, and Lawrence Berkeley National Laboratory (try saying that in one breath), one would find that the debate doesn't get any clearer.
If you are not familiar with the link that I posted, what you will find there is that you can enter information on various window designs and glass configurations for various parts of the country and get a comparison of estimated annual energy cost. The results can be very interesting.
LoE-178 (LoE, not LoE2 or LoE²) is Cardinal's single silver coating. It would be considered a moderate solar gain coating while most hardcoat LowE coatings would be considered high solar gain coatings.
In general, the high gain coatings will allow about 14% more solar gain than a moderate gain coating. But, the moderate gain coating has about a 12% improvement in (lower) U-factor versus high gain coatings. And that doesn't address low solar heat gain coating performance versus moderate and high.
Check out the link and see what you find there.
Edited 5/20/2008 7:11 am ET by Oberon
For whatever it's worth I have K&K windows in my own home. I choose those after a fair amount of research. My decision was based on value, energy efficiency, and VT (VLT) performance. When I was looking at windows the big box stores had Pella and they were very dark. Can't really remember any other specifics, but my point is that in your window search compare VT #s as well as the other specs. All these different specs, technologies, etc can get confusing. Really, the base specs are U-value, SHGC and VLT.
Let me also mention that although I said "value", K&K aren't cheap...
Edited 5/14/2008 7:19 am ET by Matt
Thank you once again. Very helpful.Spheramid Enterprises Architectural Woodworks
click here for practice clicking
Thanks for a great explaination on coatings. What should I ask for in a coastal climate where a warm summer day would be 70 degrees. I want maximum insolation and minimum heat loss .
Maximum insulation will be a triple pane window with softcoat LowE on surfaces 2 and 5 and a krypton fill (narrow IG airspace) or argon fill (wider IG airspace).
Go to the Windows Collaborative website that I posted earlier and you can play around with their energy calculator and do some comparisons.
And you are welcome...
I wrote "insolation" i.e. heat gain from the sun. What I want is a window that allows as much energy from the sun to come in, yet provides good insulation from a cooler outside temperature. Great info from you.
Keeping in mind that while insulation is intended to block thermal transmittance, and insolation (as used here) is intended to maximize a certain portion of thermal transmittance - one has to consider that the better the insulating value of the window, the worse the potential solar heat gain and conversely, the more potential for solar heat gain, the lower the potential for insulating value.
As in most things, there are compromises.
At one extreme you get maximum solar heat gain using one pane of clear glass. Of course your losses thru that single pane, when the sun isn't directly shining on it, will far exceed any potential gain thru it. And your heat gain thru a single glass pane in summer...
At the other extreme is the triple pane window with a dual or triple softcoat on surfaces 2 and 5 and inert gas fill will result in a window with an R-value (and while I dislike using R-value for windows, it fits this post) up to 10 or so. But with the understanding that direct solar heat gain is extremely low. There is now an IG on the market that claims an R-20. I believe the claim, but I am not all that comfortable with the technology. People may find that availability of this product is somewhat limited.
About halfway between those two extremes would be a window that would be both moderate solar gain and moderate insulating value. Moderate solar gain can be achieved using a single silver softcoat LowE in a dual pane IG. This unit would also result in a moderate R-value.
Changing the single-silver softcoat to a hardcoat LowE increases direct solar heat gain (about 14% over the moderate coating - depending on which coatings used and other IG considerations), but loses insulating value (about 12% - again depending on coatings used and other IG considerations).
Changing the single-silver coating to a dual silver coating and you have gained R-value over the moderate/moderate, but you have also cut down on direct solar gain.
Going back to efficientwindows.org, you will find that the three different options do tend to balance out. High solar heat gain (less insulative value) windows tend to be a definite advantage in northern homes in winter, but also tend to increase air conditioning costs in summer - and overall tend to be a little less "comfortable" because of wider temperature fluctuations on the glass surface versus low solar gain / higher insulative windows.
A higher insulative (but less solar gain) home tends to be better "balanced" year-around, but there are added heating costs in winter (versus high solar gain), and there can be something of a loss of the "feel-good" feeling of enjoying warm sun thru the windows on bright, sunny winter days. It may be primarily psychological, but it is absolutely real for many people.
Edited 5/23/2008 7:47 am ET by Oberon
Edited 5/23/2008 7:52 am ET by Oberon
Edited 5/23/2008 7:53 am ET by Oberon