I suggest take a look at the ProVia Endure high grade vinyl window.
Triple pane is what I sell now and has very low U-factor and air infiltration.
I love their low profile slim casement window, just ... read more
Abe nailed the answer for you.
If the windows are due for replacement, look for a window with offset glazing or an option of laminated glass inside the standard set of windows.
Dedicated STC windows w ... read more