You want the lowest U factor that your budget will allow. Triple pane with krypton will provide that, although argon is much more affordable and will provide the best bang for the buck. Low-e is a given unless your building is designed for a high solar gain window (even then there are some very high solar gain coatings available), but you do want to try and keep the shgc up within reason while getting the u factor down. In general, I prefer to look at the ratings rather than get hung up on the details of the types of coatings used etc, as the ratings tell you how the unit will actually perform.

This post was edited by HomeSealed_WI on Tue, Jan 21, 14 at 14:22

+1

Chicago weather is nothing to shake a stick at.

Highly efficient glass and, just as important, in a supremely air tight door and system.

I live in Chicago, and posted a question about LoE coatings when I was replacing some windows. The windows have a SE exposure. I think Skydawggy's advice of "IMO 366 glass should only be used in a cooling dominated climate such as Texas, Florida etc." was the most key in my decision. But you can read the various opinions on my thread which I'll link, and decide for yourself based on your situation. I opted for LoE 272, and am happy with my choice.

Here is a link that might be useful: Thread about LoE 272 vs. LoE 366

This post was edited by Mrs_Nyefnyef on Sun, Jan 26, 14 at 11:31

Higher SHGC on the South facing windows, higher efficiency (triple pane) recommended on all other elevations.