This friend contemplated the one dog door I have, that came with the house, in back, which is about Cocker spaniel size. He made a comment that it would have to be seriously enlarged to accommodate an Irish Wolfhound.
I told him that my regular doors ARE dog doors.
Our smarty-pants Wolfhounds know how to turn doorknobs with their mouths to open a door. Besides, Harry demonstrates how a regular sized-door pretty much serves as a Wolfhound door:
Come on in ... especially if you have a treat!