Another option for your windows would be to use a Jeld-Wen ‘Zap Pack’. This basically is a replacement sash kit that includes jamb liners and can be custom sized with either primed wood or aluminum clad exterior. As a Millwork trainer for the Big Orange Box, my students are always amazed at how fast and easy they go in and many of them have changed out the sash in their own homes after seeing the video.

You didn’t say IF you were doing new or replacing, but keep in mind a simulated divided light will be less efficient, but the worst would be a TRUE divided light with all its spacer bars.

Lastly, the U-value is the NFRC’s way of rating window efficiency. A lower U means better insulation. Think of it as 1/R, so a window with a U-value of .33 is the same as a wall with an R of 3. While the numbers may seem impressive to go from a U of .40 to a .33, you’ve really only gone from an R of 2.5 to 3.

For more info on Zap-Packs, see JELD-WEN.com