Pete,
Do you have cat doors in walls? Did you install them during the house construction or afterwards? Do you have any cat doors in exterior walls/doors? How well insulated are they? My general impression is that most of the pet doors are not insulated very well; you might as well just have an open hole in your wall.
Obed
We have them on both inside and outside walls. We framed then up so they could be attached just like it was a hole in a door. After drywall, we had to line the inside with nice wood, and then do trim to match the doors. All the door were in during construction and inspection. We consulted with the inspectors so they knew they were coming. The little cat doors cost as much to have trimmed out as the big people doors. Same details, just a change in the amount of material. Due to the small size, the scale the tolerances were a bit tighter than the people doors.
On door goes outside to an open deck, you can see both sides and the trim work before the door was added. We close that door at night: stick in a piece of white foam insulation (you can see it on top of the door in the picture) and put down the flap and lock it. The other door (shown just on the inside of the house) goes out to a screened in deck, it's open all the time. We put a different door here, it has a magnet in the bottom of it so the wind doesn't blow it open as easily.
The doors are not insulated, but they are less than a square foot of surface area. The leakage isn't an issue for us. It's far better than an open hole- if you hold it open you get a lot of breeze through it. The house has spray foam insulation so it's pretty tight. We did the door pressure test with the cat doors, no problems. Sometimes when it's cold the cats just site at the door. All the smells and none of the cold weather, cat paradise.
Finally, we have a catwalk around the main living room area. You can see where we put both an interior cat door from the 2nd floor into this cat walk (the shot with mini and me), and where we put some cat stairs in from the 1st floor to the catwalk (no door, you can see the 1st floor door at the bottom left). It's a fun architectural detail that also breaks up the high ceiling room a bit. The engineer in me likes the functionality of a catwalk in addition to the form of it all. There is also LED up-lighitng in the catwalk.
I also put in a cat-5 cable by the two outside cat doors. Someday I'll build a 180 KHz loop antennae for RF ID and combine that with a motion detector so we know which cats are inside or out. You can see the cover box on for this in the 1st picture (closeup of door from the inside). Fun project for another day...
Pete