Dog and cat doors that allow your pet to freely come and go are a great convenience to the pet owner. You can even install these pet access doors as a patio door insert so that you don't have to cut holes into walls. Although the pet door itself can last many decades, you will often need to replace the flap. Constant use and exposure to the sun and cold can damage and crack the flaps. There are replacement flaps available for many pet doors, and making the switch is simple to do.
Determine the brand of your cat or dog door. Somewhere on the pet patio door insert is the brand name; it may be on the door or the flap itself.
Measure the inside width and height of the pet door opening. This is the size of pet door that you need to replace.
Find a source for your replacement flap, and buy the flap. Your local pet store may carry replacement flaps or may be able to place a special order. You can also find most cat or dog door replacement flaps at online pet retailers.
Remove the old flap by detaching it from the hooks. Each brand may have a slightly different installation method; however, most flaps attach to the inside of the top of the pet door, which you can pull off easily.
Attach the new pet flap. To attach, line up the holes at the top of the pet door flap to the hooks on the inside of the top of the door.