How many kinds of air filters?

I have to admit that my fiance does way more around the house than I do, but of course, I do lots of housework and laundry and cleaning! But my fiance Jon does all of the home improvements and all of the repairs around here, and for instance, Last weekend air conditioner stopped working for some reason! There was just warm air coming out of all the air vents and the house just wasn’t cooling down, and we had the air conditioner turned all the way down on the temperature control, but nothing was changing, and so Jon went down to the oil furnace room in the basement to see if he could figure out what the issue was with the a/c… I heard him messing around with the central air conditioner in the basement, but there still wasn’t any cool air coming out.

  • Jon called up the stairs to get me to come down from the living room.

I went downstairs to the oil furnace room and Jon was holding up a gross looking air filter. It was black with dust and dirt and it looked like it was completely jammed up. Jon said that it was no wonder that there was no cooling going on with our a/c. He wanted to work on cleaning out and blowing all the dust and dirt out of the a/c system and so he wanted me to go to the hardware store to pick up a new air filter for the cooling system. I left to go to the store, but when I got to the heating and air conditioner area, I saw that there were dozens of filters that would fit our a/c. I had no idea which air filter to get.

 

How many kinds of air filters?