Is your existing door a solid wood door? What kind of wood? Can it be restored?

Unless the exisiting door is rotten or there's something terribly wrong with it, or it was a cheesy replacement for the original door, I think I'd try to preserve it. Old solid doors were typically made from very heavy, thick, sturdy lumber. They're almost always to be preferred over the flimsy mass produced doors sold nowadays in the local big box home centers.

I agree 100% with jamesk. If it's the sealing that you are looking to improve, there are various weather sealing products that are very efficient.

I wouldn't use the small fiberglass door because I think it's going to look odd with 5" of fill on either side.

What is wrong with the existing door?
Most of the heat loss from doors and windows is from infiltration. Even an insulated door or window has a pretty bad R value. This is sort of hidden by using U values.
The conversion is rather simple. R = 1/U.

Resource Conservation Technology, Baltimore, MD has a large assortment of weatherstripping details that are not to difficult to install (and some are very easy).

Thanks for the responce. The only thing wrong is it is old. The door is painted in several layers, and has planes of elongated glass, which is not very appleaing. Also the storm door (42 inches) is on its last leg. The door is not really that thick. My wife likes the look of a textured fiberglass door. What would be the dollar factor to get this door refinshed by a pro? Also any ideas on going with steel door @ 42" or a prehung fiberglass@ 36 " THANKS!!!!

What's the door height........Most wide doors I see are also grande in height also........

We had a solid oak door, which had deep gouges and paint stuck in the gouges, refinished/stained for $325. It looks wonderful now. We're in the Chicago area.

I also have a 42 inch door -- metal -- and to replace it with another is exhorbitant. But it must be 42 inches, bec. of hugh sofas.
Is there a way to dress it up -- drill a window, add wood -- so it looks like a log cabin door should?
Thank you.
JJ

I just dropped off a 36" old wood half-lite door at the refinishers yesterday. They estimated 3 weeks and $175-$200 and that includes filling a lot of old screw holes and patchwork.

Any chance you could post a picture of your door as it's installed now? That might help.

Sandy