Inadequate filter area?


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.
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On 7/17/2010 7:05 PM, snipped-for-privacy@gmail.com wrote:

Try a high quality pleated air filter, that type has more surface area. I like 2" thick filters myself and will always install a 2" filter grill or housing on any new job, especially commercial buildings. Ask your contractor if you can get set up for 2" thick filters, it's a lot less expensive and simpler than those newfangled super duper air cleaners with a cartridge the size of a Buick.
TDD
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Sure you can! You what they say? "MONEY TALKS AND SHIT WALKS"
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