new windows -- how many layers of glass?

[kilgor25]

I'm replacing all of the original windows in a 30-year-old house. This winter's heating bills killed me. I've had three contractors give estimates. Two of them pushed the triple-pane windows, while the third said it wasn't worth it and offered double-pane.

I only found one other thread on this forum discussing the issue, and the triple-panes were dismissed as "a scam." However, both salesmen (I know, it's their job) showed me the "heat lamp" demonstration. The triple pane definitley kept the heat and cold from moving though compared to the double-pane. Of course, I don't know what, if anything, was special about the double-pane sample they showed.

Could this have been a rigged test? Do the double panes that are used nowadays offer as much protection as the triple, or is there really a value in spending the extra dough?

[grumpydasmurf]

Dual pane glass is typical. I've heard of triple pane and seen web sites with the information, however in the Chicago area I've never seen the triple pane glass. Did they show you the heat test witht he triple vs the double? If it was triple vs single ofcoarse it will make a big difference! I'm curious what triple vs double would be.

I would doubt the test is rigged. With argon insulated glass and Low-e, the tests are honest. However my thought is this: Is there really a difference between double vs triple?

Are your attic and walls insulated?

[Rich]

Double pane is more than adequate. Triple pane is a selling gimick. If you really look at the triple pane windows the 3rd pane doesn't even have a thermal barrier - it's removeable in most configurations. With double pane you can get all the coatings and gas filled to do just as well as a triple pane.

[kilgor25]

Yes, the heat test was double vs triple. I'm wondering if they choose the worst sample of double for the comparison. The heat was noticeable through both panes, but not through the triple.

[Rich]

Well I'm currently with contract with Pella for over $100k of windows and they've said that the triple pane is a gimick. That's all I'm basing my information off from. These will be placed in CO where cold/heat/wind are pretty big issues.
Probably a bigger factor than the triple vs double is correct installation - taping the edges, insulation, etc.

[linear]

So it's kinda like the razorblades, eh? :D

There ought to be an NFRC label that details the specs. That can at least help in quantifying the difference.

I found these sites kind of useful (thanks Uncle Sam):
http://www.efficientwindows.org/
http://windows.lbl.gov/pub/selectingwindows/window.pdf

Whether the cost of upgrading is worth it can differ by where you are building too. There's a nice gizmo to help you sort that out too:
http://www.efficientwindows.org/selection.cfm

FWIW, I used Hurd monument series with low-E glazing, the typical U-factor was 0.29 or so, which I believe places them on hte more efficient end of the spectrum. Upgrading my whole house to those from the double glazed, non-low-E cost 800 bucks. I could see the payoff being within reach for that upgrade, so I bit.

[Dano]

I would have the salesmen do a cost pay back period in relation to energy savings vs. additional cost. They should have all the ratings to compare against. Most likely in the 12-16 year range and not worth it.

[jjcold]

I'm inclined to think the triple pane windows are a gimmich. But I wonder, when the industry moved from single pane to double pane so many years ago, I'm sure there were a lot of people that figured double pane windows were a gimmick, too.

I would say, get an excellent quality double pane window and insulate very well.

[Oberon]

The original post here is quite old, but I am going to dig it up and make a couple comments if folks will bear with me.

First, triple pane is not a gimmick. Triple pane can be a good bit more efficient than dual pane provided a few criteria are met.

First, the really efficient parts of any window, dual or triple pane, are the spacer (the thing that holds the two or three pieces of glass apart), the application of a Low-E coating, and the inclusion of an inert gas between the lites.

The spacer may be made of several different materials, but the newer spacers available are all made to be called "warm-edge" in the industry. Warm edge includes TPS, SuperSpacer - which is primarily silicon, Swiggle - which is a foam product with a metallic core, Cardinal XL - which is a very thinwall stainless steel, and Intercept - which is also a stainless steel product with a foam coating.

So, all that means simply that a "warm-edge" spacer system makes for a warmer window.

Next, Low-E coatings. There are two types - hardcoat and softcoat.
Softcoat is better.
Hardcoat is basically a layer of tin oxide applied to the glass while it is still semi-molten in the float glass process.
Softcoat is applied in a vacuum chamber to "finished" glass in multiple layers of metals and metal oxides. One or two layers of silver is the secret behind softcoat Low-E.

A single layer of Low-E coating on the inside of an IGU (insulating glass unit) in a dual pane application makes the window MUCH more efficient than a triple pane with clear (no Low-E) glass. BUT, what if the Low-E coating is applied to two inside surfaces on a triple pane unit?
hmmmmmmm...actually works really well in that case.

Next, we have the "gas". Two primary gasses are used in IGU's, argon and krypton (okay, there are several variations, but this is already long enough!).
Argon is basically a byproduct and it is relatively inexpensive. Krypton is much more expensive, so for the most part, argon is used in dual pane applications. But, some companies offer krypton in triple pane applications and argon in dual...why?

Because of the nature of the two gasses, krypton is MUCH more efficient when used in a narrower space. Imagine a triple pane IG with two 1/4" airspaces between the lites. In fact, at that narrow width, argon isn't really that much better than air. BUT, krypton is actually at its peak efficency at that width.
Argon gets much better at wider spaces and at about 7/16" peaks in efficiency...which just happens to be a very common airspace width for dual pane IG's...go figure.
Krypton is still slightly better than argon at 7/16", but not enough to make using krypton worth the extra cost.

And I haven't even mentioned Xenon!

[mjpliv]

It should be mentioned that Low-E coatings are not an insulator. They do reduce one form of heat loss. The molecules of metal comprising the Low-E coating allow short wave radiant energy, like that generated by the sun, to pass through the glass (or about 90-95% of it anyway). This heat energy warms up the carpet, the couch, the walls and what ever it finds inside that will absord radient heat. As these objects release that heat it is in long wave radiant form. When this heat energy reaches the Low-E coating it is reflected back into the house. Your heating system generates heat in a long wave energy form (unless you are heating the house with heat lamps pointed at the winds) so the majority of that radiant heat is reflected back into the room.

Insulators such as Argon and Krypyon help slow conductive heat loss due to their inert properties as well as slowing the convection cycle between the lites to keep the inside glass surface as warm as possible.

[grumpydasmurf]

Ok after some research...

I dont see a cost benefit to go from double pane to triple pane. Are the triple pane better? Tests prove they are, but not by much... and you have to pay a lot more for them too.