Good golly Miss Molly, I did not say that rest of the unit is immaterial. I only stated that the OA glass unit, and the the Low-e selected is a very big component of the overall effectivness of the the unit. Millworkman, you are absolutely right about the aspect of a poorly constructed window. As regards to adequate weatherstrip, I've got my opinions on that one too. Most window companies that manufacture easy-tilt windows use "finseal" weatherstripping. This is a "woolpile" with a thin film of plastic designed into the pile to stop air infiltration. Most window companies have two rows of the "woolpile" designed into the systems. Premium window companies have three rows of this weatherstripping. A lot of other systems rely on a jambliner with a foam backing to "press" the jambliner against the sashes. This system makes the window easier to install because the window can be slightly "out of square" and still perform adequately. The problem, for a consumer standpoint of these systems, is that the sashes are more difficult to tilt-in. The "Achilles heal" that many companies have is the sill tower. Many companies do not have "finseal" designed into the sill tower, which can cause massive air leakage. As far as whether or not 0.29 is a good U-value: hey, shop and compare. I'll say this, I've seen a lot of numbers out there and there is a lot of distortion out there. Numbers can be manipulated by the size of the unit tested. I've seen it, I've personally been to the testing labs and I know what some people are doing. A lot of the purchase decision is going to made by the reputation of the manuacturer as well as the reputation of the distributor. OK, now about materials: *Is wood a good insulator: yes. *Is vinyl a good insulator: yes. *Is fiberglass a good insulator: yes. *Is non-thermally broken windows good insulators: NO. *Is thermally broken aluminum windows good insulators: Somewhat Regarding the differences between the energy efficiency of wood vs vinyl, the differences are marginal. To millworkmans point, the quality of the manufacturing plays a big role into the overall efficency of any window.

The Infinity is a better product as it stands right now. It is my understanding that the Milgard is due for a re-design but I will withhold judgment until I see that window.

You may be 100% correct, lzerac. I have not sold Eagle products in a few years and they very well may have improved the quality but I just do not feel Andersen products are a top of the line product, either performance or durability wise. The 400 and Tilt Wash Double Hungs which make up the bulk of their sales are a vinyl wrapped frame which is not very think nor attractive from my perspective. The sash are not architecturally correct in that the sash are essentially the same top and bottom and do not give you the aesthetics that a wood window should have. The exterior of the sash are still a painted product and the glass is only 5/8" of an inch thick where as most companies have gotten better performance values from thicker glass. This is just for starters I do not sell wood windows currently and need to think back to some of the other reasons I am not a fan. I used to sell a hell of a lot of Andersen Windows but then I started selling Marvin and Kolbe and just found the workmanship and the quality if the products to be of a higher quality. I personally feel that when Andersen started making custom products and purchasing other companies that this was the downfall of them as they started trying to be everything to everybody instead of being themselves. Just my feelings and opinion forr what that is worth.

A new construction window does not always mean more glass. It depends on window type and size and manufacturer. When we replaced our old leaky Aluminum windows with AL clad, wood interior windows (Marvin Ultimate), we ended up losing about 6+ inches of glass. The old aluminum had skinny sash while the new ones have large wood pieces inside. The large wood pieces did not affect the views as we feared but they certainly did not yield more glass. There are several reasons to stay with replacement even when changing siding and trim. We lived through this in our previous house. When trim around the windows is expensive to replace and already matches the house trim. WHen original frame is sound and we are not changing window size. When replacement window is sufficiently better than old window. When project cost of new construction is way higher than replacement windows. WE ended up using replacement windows for our previous home. For our current house, the trim was bad and needed replacement anyway, the framing surrounding the windows had visible water damage and there is no replacement for those poor quality Aluminum windows. The end result was new construction windows.