Hey folks I got a question for you: if we have let's say a 5 ton air handler, with rule of thumb requirement for return air filter area of 200sq in/ton, give or take, why manufacturers make a spot for a 22x22x1 filter in the air handler/ furnace? It is so undersized, especially if people use pleated filters. And no notes in installation manuals about increasing filter area/proper calculations. I work for a big company, they have couple of dozens stores and every single 4 or 5 ton system either has filter in the AH or has just single 20x20x1 filter rack. Filters get plugged real fast, and then of course "No AC" call.
Also if anybody knows good online store to get all duct parts(take-offs, ceiling grills and especially ceiling return boxes - I can't find them!!!) i'd really appreciate info. If links are not permitted, please send me a PM.