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Windows: triple pane versus double pane with 4th surface coating?

dsummers | Posted in General Questions on

I am replacing all of the windows in my house (Denver area, Zone 5B) and trying to decide between triple pane windows or double pane windows with a 4th surface “heat lock”  coating.    My house has a mix of sliders and single hung windows.

The majority of my windows face West, and it gets pretty hot in my area in the summer.  In terms of comfort, cooling the house is more difficult than heating, so I am looking for a window with a low SHGC.  

I have quotes from the same contractor for

1. Anlin Catalina series vinyl double pane windows with Anlin’s  “Quadratherm” 4th surface coating.

2. Pella 250 series triple pane with their standard “advanced low-e” coating.

The Pella windows are about 15% more expensive than the Anlin.

Both windows have similar U values (average of 0.21 for the Pella and 0.23 for the Anlin).   My contractor is really pushing the Anlin as being the better window at a lower cost than the Pella.

I have read that the 4th surface low-e coatings can increase condensation in the winter, and I worry a little about having a coating on the interior surface of the window.

Here are my questions:
1.  Which would you rather have in your house?  Triple pane windows or double pane windows with the 4th surface coating?

2.  Are the 4th surface coatings a proven technology by this point that I can expect to last for 20+ years, or is it still too new to know if there are any long term durability issues?

3. Which is going to be better at sound reduction?   Triple pane, or double pane with mis-matched glass thickness (Anlin’s “Sound Package”)?

Thank you,

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  1. [email protected] | | #1

    Both companies use Cardinal glass/coatings, so an apples to apples comparison there. Also both companies use Cardinal's IG system for some (most?) products, but not for all, so that could be a consideration in some cases.

    1. For zone 6 or higher I would go for triple pane over 4th surface coating, but in zone 5 both could be considered as viable options.

    2. The 4th surface coating technology is totally proven and will last for decades with the caveat that cleaning with razor blades or steel wool is probably not a good idea and certain cleaning agents should also be avoided - per manufacturers instructions.

    3. Depends....Although sales folks and others often claim that triple pane is the end-all for sound control performance, actually the addition of the third lite may not offer any sound advantage over dual pane.

    More important than the number of lites is the width of the airspace between the lites. For example a dual pane consisting of two 1/8" lite with a 1" airspace will have pretty much the same sound performance as a triple consisting of three 1/8" lites and two 1/2" airspaces. The downside is that an airspace wider than about 1/2"-3/4" (depending on glass thickness) begins to lose energy performance even though it blocks more noise. When using a triple it's possible to have the best of both worlds - optimum airspace width (x2) for energy performance as well as wider combined for sound performance. Conversely, a triple with two narrow airspaces may not be as good at blocking sound as a dual even when the two lites in the dual pane are the same thickness.

    However when the two lites of an IG unit are the same thickness they each allow sound waves at the resonant frequency of the glass sheet to pass with little propagation loss. This is known as coincidence dip. unequal thickness lites improves sound blocking performance because the different glass thicknesses resonate at different frequencies and attenuate the wavelength that passes easily through the other lite - nice and neat - as long as they don't come in a narrow (less than 7/16") airspace for best performance.

    4. Have you discussed altitude? How high up are you and will the IG units contain argon or will they have capillary tubes?

    5. What LoE coatings are being suggested? For west facing windows for rooms that overheat because of high solar gain, you need something to block that excess heat gain, but the potential downside is that the glass may need to be darker. If you are olay with that then ask Anlin about their LoE-452 option.

    1. dsummers | | #3

      Thank you for the reply. I'm at 5400ft altitude. Some manufacturers will deliver Argon filled windows here (without vents), but others do not. Anlin and Pella both can deliver windows without capillary tubes according to my contractor.

      As for coatings, the Anlin windows were quoted with SunMatrix both with and without "Quadratherm" which is the 4th surface coating. I think that the SunMatrix is the same as Cardinal 452 since it is advertised as a 4 layer coating.

      The Pella 250's are with the Pella "Advanced Low-E" which is (I think) Cardinal 270.

      My existing windows are Milgard triple pane with the Cardinal 270 coating and we are very happy with them in terms of SHCG and VLT. They are the thin IGU triple pane (same thickness as double pane), so the U factor is only a slight improvement over double pane.

      Going with the Pella gives us identical SHCG and VLT numbers as our existing windows (since it is the same coating), but a better U factor because the Pella has bigger air gaps between the panes. Unfortunately Milgard closed their Denver plant and we can't get Argon filled windows delivered here any more.

      The Anlin's with the SunMatrix and Quadratherm (4th surface) have a slightly better U than my existing triple pane windows (but slightly worse than the Pella) , similar VLT, and lower SHGC.

      I'm sure that I would be happy with either choice. I feel like the Pella's are the closer equivalent to the windows that we are replacing.

      We like our current windows with a VLT around 0.4. I find that it takes the harshness out of the afternoon sunlight. Otherwise we just close the drapes which have a VLT of zero. :) That will be even more important since all of the shade trees in my neighborhood burned in the December fire. We will not have any shade to the west for the next 10 years while the trees regrow.

      I think that your reply, and Bill's below has convinced me that either window will work for me.


  2. Expert Member
    BILL WICHERS | | #2

    A true triple pane window will be more comfortable than a double pane with a 4th surface coating like Cardinal's i89. To really get the full benefit of a triple pane window though, you really need a full-thicknes 1-3/8" thick IGU. IF you go with one of the 7/8" triple pane IGUs, you won't get the same performance as a full-width IGU. You can go with Krypton fill to partially make up the difference, but it's expensive. I personally would try to go with a full-width triple pane IGU, but not all manufacturers offer that as an option.

    i89 is not likely to fail on you. Exposed glass coatings aren't a new thing, and the manufacturers know how to make them durable. The only issue is with scratching from abrasive materials, but that can damage the glass of the pane too so it's not just an issue with the coating.

    If the "sound package" with different thickness lites includes one that is LAMINATED glass, it will win against a triple pane IGU that has three identical thickness lites. Different glass thicknesses helps to damp resonanances so there are no "magic" sound frequencies that can get through the IGU at resonant points. Laminated glass has a sheet of plastic bonded between two pieces of glass, so it damps vibrations much better than solid glass (you can easily hear the difference by knocking on the glass). A typical car windshield is made of laminated glass. Triple pane windows by themselves, with no other design changes made for sound attenuation, are only a little better at reducing sound compared to a normal triple pane window.


    1. dsummers | | #4

      Thanks again Bill.

      the sound package is just different thickness glass. Not sure if they offer a laminated option, but I'll ask.

      Pell advertises their triple pane as a 1" IGU. My old windows are Milgard Tuscany triple panes where the IGU is the same thickness as a double pane (5/8 maybe?) and the U factor benefits are marginal. I seem to remember at the time that there was a 15% price premium for triple pane to get a 10% better U factor.

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