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Low-E windows

cmiltier's picture

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?

(post #82417, reply #2 of 67)

Suprisingly enough, both HD and your lumberyard are incorrect.


(post #82417, reply #3 of 67)

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

(post #82417, reply #9 of 67)

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

(post #82417, reply #4 of 67)

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.   

(post #82417, reply #5 of 67)

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.

(post #82417, reply #6 of 67)

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 ..

(post #82417, reply #7 of 67)



(post #82417, reply #11 of 67)

So over years, will a low E window be darker -- less light/view coming in?

(post #82417, reply #13 of 67)

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.


(post #82417, reply #15 of 67)

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?

(post #82417, reply #19 of 67)

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

(post #82417, reply #21 of 67)

And They are softcoats?

(post #82417, reply #23 of 67)

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

(post #82417, reply #30 of 67)

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. 



(post #82417, reply #34 of 67)

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

(post #82417, reply #35 of 67)

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


(post #82417, reply #37 of 67)

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.

(post #82417, reply #38 of 67)

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?


(post #82417, reply #39 of 67)

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.


(post #82417, reply #25 of 67)

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 ²

The 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

Fredericksburg, VA


Jon Blakemore

Fredericksburg, VA

(post #82417, reply #31 of 67)

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....

(post #82417, reply #53 of 67)

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

(post #82417, reply #52 of 67)

Okay...I'll try it:


edit: capslock on:


Bob's next test date: 12/10/07

Edited 5/17/2008 10:29 pm by Jim_Allen

(post #82417, reply #54 of 67)

Use the keypad on the right side of the keyboard.


Jon Blakemore

Fredericksburg, VA


Jon Blakemore

Fredericksburg, VA

(post #82417, reply #41 of 67)

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


(post #82417, reply #42 of 67)

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.


(post #82417, reply #43 of 67)

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

(post #82417, reply #46 of 67)

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.

(post #82417, reply #48 of 67)

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