energy efficient home improvement credit

[sndy2521]

Do energy efficient products like windows count if their are a part of an addition to your existing main home or is it only applicable when you are replacing an existing window/door/insulation etc.

[Opus 17]

You can include them if they are part of a new addition.

You generally can't include efficient improvements that are installed in a new house you are buying, because the builder is entitled to those credits (and they are different).  But it's fine to claim items installed in a new addition.