I recently bought a new home. When going to change the furnace filter, I couldn't get the original furnace filter out of the slot at the last part of the filter (where the cardboard border is). Since it was a cheap used filter, I wasn't too worried about destroying it, so I just kept yanking while holding the air duct in place, and eventually ripped it out. After removing the old filter, I noticed that the top lip of the furnace filter slot, going into the air duct, was bent downward a little bit. It's not bent a lot, but enough that the cardboard will get caught while removing the filter. It is a major pain.
I tried getting a hammer in the tight (1") opening, but I couldn't seem to do anything with a hammer. I tried bending the metal metal with my hands, but the metal would just go right back to where it was originally. I want to get a nice permanent electrostatic furnace filter, but I am scared that I will put it in there and never be able to get it out to clean it. Cardboard will rip and break, metal will be a little harder to destroy to get it out of the air duct. Does anyone have an idea on how to fix this problem? I really don't want to have someone come out and replace the air duct just for one small bent piece of metal. Below is a picture of the setup.