snowlover,

It really depends a lot on your requirements.

First, a dual pane window with a LowE2 coating and argon gas will outperform energy considerations  a triple pane window made with clear glass.

As a generalization, triple panes can come in two varieties  one version has a relatively narrow space between the lites  kind of like taking a dual pane and dropping another lite between the first two and the second version has a wider spacing between the lites - kind of like taking two dual panes and removing a lite from one and slapping the remaining parts together.

Both work, but there are some differences worth considering.

For energy performance, the narrow airspace version works best when two surfaces are LowE2 coated and krypton gas is used between the lites. Krypton gas performs at its energy-saving best in a narrow space of about 1/4" or so...which happens to be the typical space between the lites in a narrow triple pane. This configuration is very energy efficient and works really well...but the downside is that this version can be expensive.

The wider triple pane version would generally have an airspace of about 7/16" between each lite plus or minus a little and again the advantage is in the LowE2 coating on two separate lites within the unit. In this case, argon gas would be the most cost effective fill  rather than krypton  because argon is cheap and plentiful and at the 7/16" spacing is almost as good as krypton in performance numbers  not quite as good  but the slight insulating advantage of krypton in this configuration doesn't offset the additional cost of krypton.

The biggest disadvantage of the wider triple pane is the physical size of the IGU Â or more precisely the width of the glass package.

While manufacturers who use this version build their sash to accommodate the IGU width, not all companies can or will do so, so not all companies offer a triple pane package.

In general, the wider version triple pane may have slightly better energy numbers than the narrower version if both use argon or even air infill between the lites.

Again, in general, a triple pane will outperform a dual pane in energy considerations assuming that both units have pretty much the same bells and whistles.

One interesting potential downside to the increased energy efficiency of the triple pane is the likelihood of increased EXTERIOR window condensation on cool mornings.

Often, people who replace energy deficient single pane (or even clear glass dual pane) windows with more efficient LowE coated windows become concerned that their windows are having problems with exterior condensation  usually on cool mornings.

This is actually quite normal and indicates that the windows are performing exactly as they are supposed to do - by increasing the energy-blocking performance of the window it is quite possible to increase the likelihood of exterior condensation. Not a problem  in the sense of a window flaw  but some people do find it objectionable.

To me, this wouldnÂt be a reason to reject increased energy efficiency, but window manufacturers do receive complaints  some rather vehement  about this exact issue.

Either way, a little sun-heat fixes that problem pretty quickly. Although in certain areas of the country it is actually possible to have frost or ice formation on the exterior of super-efficient windows in the winter time  which beats having it on the interior of the window I would suggest.

But you were also asking about a triple pane windows increased ability to block sound over dual pane...and while some folks will suggest triple pane glass for its sound deadening ability, overall there is no difference in STC rating between triple and double pane provided that the overall airspace between the panes is constant between the two constructions.

In other words, a triple pane with two 1/4" airspaces and a dual pane with a single 1/2" airspace...both using 1/8" glass...will have identical STC numbers as long as the IGU's are the same dimensions (and the other components are of equal quality).

Earlier I mentioned that triple panes can come with a wider airspace or a narrower airspace. This isn't exclusive of course, but it works as a general guideline for illustration.

As said if the total width of the airspace is the same between a dual pane and a triple pane then the basic sound blocking ability will be comparable.

But, what happens if the dual pane has an airspace width of 7/16" (for example) and the triple pane has the wider spacing combination of two separate airspaces and BOTH are 7/16"?

Well, now we are dealing with a different set of assumptions and in that scenario the triple pane will significantly outperform the dual pane because of the overall width of the airspace.

The width of the airspace can be a huge determining factor in sound performance - potentially much more of a factor than an additional lite of glass. So the argument of triple versus dual relates more to the space between the glass and not the number of lites...getting more complicated, isnÂt it?

Ultimately, buying a good quality unit and making sure that it is installed correctly is going to go a long way in improving both energy and sound considerations.

If you would like, we can get much more in depth about this stuff...

Really appreciate all your time and information.