what is the filter size for a tempstar model fsm2x3000a air handler

My new Goodman GMVC91155DX Furnace is about to be installed. I need to know what size filter to by. Spec sheet says it takes a 486.. I have never seen filter sized like this? Can anyone help me covert the size to something I can buy?

I just moved into a house and it has 2 electric heat pumps and 2 air movers - I guess that's what they are. I assumed they were backup furnaces, but I don't really understand after looking at the manual http://www.tappan.net/Literature/514b.pdf This is my first time having heat pumps in a house....

I have a intertherm furnace model#mmha-056aahr-05,I got the same size filters to replace the old,but man they are tight,they seem to be to large.The old are bent and sqished.the size I have are 15x20x1.Can anyone help with the proper size.Do they make a 14x19x3/4.. Thanks:confused:

What is the recommended size of filter system is needed for a 24' round above ground pool?