I recently lost my water heater door while driving down the freeway. I then discovered that there are many different doors depending on the manufacturer and model of your water heater. In addition, there is an old style door that does not match the water heater manufacturer identified doors. Below is a very blown up photo of this style door as it looks on the clipper. The door measures 12" x 12" and 1/2" thick. It opens from the bottom.
After much research, I have located the replacement for this door: http://www.appliancezone.com/ShowProduct.aspx?ID=87186