window or through-the wall air-conditioner?

You can see through the window?

I feel a through wall unit gives these benefits: A better, more solid fit; no loss of day light; better control of day light with shades.

Through wall units are available and should be available for as long as window units. They are more available in some areas than others.

Tom Baker

"John M. comcast.net>" Also, if I had to replace it down the road, would it difficult to find a

Technology is on your side. Newer units are usually smaller than older units of the same capacity. Chances are, you may have to put in a filler. Ed

"John M. comcast.net>" The contractor who's converting my 24 x 40 attic to office space suggested

Also consider a ductless system, most are near silent in operation since the compressor is outdoors and only require a 2 1/2" hole to the outside for refrigerant piping and condensate line. The lower end thru the wall (hotel style units) can be the source of much more noise than the higher end units. Which ever you choose go for a quality unit that will have a lower db output. Also if you have a need for heating you'll need a heat model or electric heat strips.