[dlhowl]

I put in the large size, 10"W X 15"H opening. I mounted it closer to the floor than what the manufacturer recommended, but the top is still 17" off the floor. It's easier for the to step over, but also left clearance for height. They could have used a smaller one by manufacturer's recommendation.

 

[dlhowl]

Just thought about other critters. My sister has Pugs, she put in a small door for them. One day she came home to find her other dog in the back porch with the pugs. She thought the kids put him out there. She put him back out and a few minutes later he was in again, he used the dog door.
OH, did I mention he is a Sharpei-German Sheperd mix, and 90lbs!!!!

 

[dlhowl]

Here's how mine is set up. From the kitchen into their pen.
(Dozer likes to lay with his head outside.)