This article is from the rec.pets.dogs: Assorted Topics, posted to rec.pets.dogs newsgroup. Maintained by Cindy Tittle Moore with numerous contributions by others.
Some points:
* Get one that at least has magnetic strips to hold the door shut. In colder climates, you might want to consider a "double door", i.e, the outer door must close before the inner one opens. This would cut down on the drafts.
* Size is deceptive. Dogs don't really need as much space as you might think to get in and out.
* Installation is usually very easy. Some models fit into patio doors and are removable. Make sure the one you get is lockable or blockable. If the door is hollow-core, it is trickier, because then you have to insert a frame in the door for the pet door to attach to.
* The wall between your garage and house is considered a 'fire wall' and you're not supposed to cut any holes in it. In particular, it could make fire insurance claims tricky. And if you sell the house, you will have to fix the hole first.
* Install the door in such a place as to make it impossible for someone to push something through it to open a door or window, even if they can't crawl through themselves. Ideally, you should have some way of locking or disabling the door for times when you are gone, say on vacation.
Johnson pet doors are frequently recommended. RC Steele stocks them. Another source is America's Pet Door Store (1-800-826-2871).
There exist electronic pet doors that are activated by a special collar. Most of these are for cats, but there are models for dogs up to 110lbs. These help keep unwanted animals from entering your house. These are, of course, somewhat expensive.
Some dogs need coaxing to use the door. Prop the door open and offer a treat from the other side. Don't try and push your dog through.
 
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