While it is true that argon and krypton are heavier than air, the reason for replacing air with argon or krypton in an IG window is because the thermal conductivity of those two inert gases is significantly lower than that of air. The panes of glass are spaced close enough together that convective looping within the trapped gas is nearly eliminated.

I have been unable to find any standards for the quantity or duration of argon and krypton in windows.  Since the gases are inert, I agree they offer more insulation to a window that contains them but how much should be placed in a window and how long will it stay in the window.  From talking to many window manufacturers over the years, none seem to know the answers to these two questions.

I have used argon filled windows but I suspect that some of the argon has escaped through the seal over a long period of time thus reducing the effectiveness.  I am now considering using triple glass instead of argon.  Which will give the best results in 5, 10, 15, 20 years?

This seemsb to be a function of sealant.  When they first started using argon in IG units, the effective lifespan was only about 10 years.  Sealants have improved so that argon remains effective (there are still long term loses) for 20 years or more.  From memory, about 70% at the 20 year mark for a normal IG unit. 

Structurally glazed units need silicon glazing for their strength and silicon is not as good at holding argon.  A silicon glazed units loses their effectiveness after 10 years or so.

The above information is from Glaverbel (Europe).  There are a couple of contributors here that seem to be in the industry.  I would like to hear their views on this subject.

Bruce

Of course the very best thing to put between the glass is nothing at all - Vacuum-Insulated Windows
(http://homerenovationtrends.wordpress.com/2008/08/08/vacuum-insulated-windows/)

I thought this was a ways out, but it seems that the technology for vacuum glazing may be close than we thing.  There's talk of an double pane window here with about an R-13 glass (not the whole window) being available possibly this year - Super-Insulating Vacuum Glass (http://greenbuildingelements.com/2008/03/17/super-insulating-vacuum-glass/)

I haven't seen any recent updates about those vacuum insulated windows. Seems pretty promising but wonder how affordable they really can get? If I had a better mouse trap I wouldn't give away the store ;)

I wouldn't want to be the first person to buy them either. There are sure to be some initial problems. Technology also improves and decreases in price. That said, if you look at the window advances even in the last 10 years or so, I think it's reasonable to expect similar in the next 10.

Really, argon and crypton very heavy gases, than air. Their heat conductivity considerably below air.

Yes.

Usually about a 20% increase in efficiency as compared to without argon/krypton.

So, here is my experience with argon or krypton gas. I think that it leaks out a lot faster that you think or the manufacturers want you to think. Yes they have made advances in sealants but can they really assure you that the gas will not leak out. They only way I know is by using an IR camera and rechecking them under same conditions on an annual basis. Here is an IR picture of a window that lost it's seal and the argon leaked out. The two windows were installed at the same time and were less than one year old, which on do you think leaked? Without the IR the only other way of telling the seal is broken is when the window clouds up between the panes. It the leak is small enough to leak but not allow circulation you might never know. I still spec this in my windows, but I cannot honestly tell a customer that it will still be there in 10 years, experience has taught me different. http://picasaweb.google.com/TomPittsley/IRPicturesShowTheTrueStory#

Tom Pittsley
[email protected]
www.eebt.org

They don't know what there windows or the gas within (or lack of gas) is going to do in 20 years. Triple pane windows were popular in the late 70's early 80's but they developed lots of seal leakage problems and condensation. I would think a vacuum in-between the panes would really be prone to leaking because the windows would try to suck air. And how do they keep the panes from bowing in from atmospheric pressure?

To answer my own question "low thermal-conductivity spacers are placed in the space between the two panes" to keep them from touching each other in the vacuum panes.

Super Peak Performance Glass

Super Peak Performance™ glass is a triple-pane glass system constructed of two glass lites of high performance LoE2 Glass and one lite of clear glass.

The two air spaces between the panes of glass contain Krypton gas. Krypton Gas increases the insulating value of the glass unit as well as providing insulation from outside noise. Super Spacer® Warm-Edge Technology seals the glass unit.

Super Peak Performance™ LoE2 Glass Performance Values*
R-Value	9
U-Factor	.11
Solar Heat Gain Coefficient (SHGC)	.37
Ultraviolet Light Transmission (UV)	4% (96% blockage)
Visible Light Transmission	55%

Also you could see the thermal picture beeing taken from a triple pane eco window that we use. Itis important how to place the window´s