(Amazon.com product link shortened)12231365&sr=8-3&keywords=aprilaire+filter+413+replacement
16" x 25" x 3 1/2"
It does a decent job but in this ancient house with two cats I'd like to go all the way to a HEPA filter.
I have not been able to find a HEPA replacement so unless anyone has a suggestion , looks like I will have to replace the entire enclosure.
Since I'm not a sheet metal expert, will have to contract this out.