I have a 5 ton air handler that uses a 20"x20" filter that is built-in
at the end of the handler. From what I can tell that is woefully
inadequate filter area for the size of the unit.
Typically I believe there should be nominally ~200 sq-inches per ton
or per 400 cfm. The setting on the handler is for 2000 cfm so I should
be using at least a 30"x30" filter or two smaller filters side by
side. The question is can I have a larger filter box installed between
the return plenum and air handler? I don't ever recall seeing a setup
where the filter is larger than the width x height of air handler (air
handler in horizontal position) .
Thanks for any input. I am going to have a contractor do some
retrofitting on the ducting due to poor performance and wonder if I
should add on a larger filter capability.