There are many things to consider when explaining how to install a pet door. If I addressed this question like a window installer that was asked to frame a window into a wall I would need to know how the outside wall of your home was constructed, ie location and supporting wall stud configuration, the outside (vinyl siding, brick veneer)and inside (dry wall, lap plaster) building materials attached to the inside and outside of that wall.
Is the location clear of utilities (electric, plumbing, cable etc.). The size of the window or in this case pet door to be installed. Lets not forget the elevation difference between the inside floor and the outside ground level the pet would traverse or the depth of the wall and tools necessary to safely finish this project with.
Our medium wall mount can be framed into walls like a vinyl replacement window or exterior door with out having to add a header. Our large wall mount pet door with a outside frame width of 16 inches wide can be attached directly to the outside side of 16 inch on center standard wall studs, This would give a recessed look with the exterior (siding etc.).
If the wall studs are wider than 16 inch on center then once again our pet door can be framed in between the studs and trimmed off in the same fashion your existing windows and doors have been trimmed on both the interior and exterior sides of your wall.
We don’t offer an aluminum wall tunnel kit because they are energy inefficient and still need to be framed in. We do offer a versatile energy efficient Pet door product at a price when compared to other wall mount products gives you a monetary difference that can be applied to the cost of installation, leaving you with a custom built draft free pet door application.
If the first two paragraphs seem a bit overwhelming, to summarize your question it may be better to ask who should install rather than how to install a freedom pet pass wall mount pet door. The answer to the second question “what is the difference in the two doors available”, one wall mount is 1 inch thick and houses both our flap system and security door. The other wall mount is a 1/2 inch thick and houses only the draft free, wind resistant flap system.