Return air duct size?

Old 12-20-03, 07:07 PM
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Join Date: Oct 2002
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Return air duct size?

I have a 2000 sq ft home with central air and heat, the units are located in the attic.

The return air duct is a drywall wall cavity from the slab to the attic, pretty standard.

When I bought the house, the return grill was about 18x18", so I installed a 20x24" grill.

The volume of air through this grill is so high that the suction bends and warps the filter eliment. I use paper type filters.

The real issue that bothers me is that as the filter loads up (slightly), there is a whistle in the duct as it pulls air from some crack, probably between the drywall and a stud.

My question is, how big is big enough when it comes to the size of the return air filter housing?

Maybe I should just forget the hi efficiency paper filters and go back to the cheap spun fiber type.

Old 12-21-03, 06:38 AM
Jay11J's Avatar
Join Date: Sep 2001
Location: Rochester, Minnesota
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I take it you are using the 3M's purple frame filter? I would just go down the next one, red frame filter.

I never like the cheap filterglass spun filters. they don't catch anything.. only 8% of the dust. so that means the blower, and coils will get dirty faster. and $$$ clean up.
Old 12-21-03, 08:25 AM
Ed Imeduc's Avatar
Join Date: Aug 2002
Location: Mountain Williams Missouri
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Exclamation Filters

You dont say What the btu is on the furnace are what the btu or tons of AC you have here are. lets take a stab at it. For 2000sq ft say you have a 3 ton AC the cold air duct back to the unit I like about 80" per ton so thats a duct with 240 sq " in it. That filter grill you put in is a 20"X24" so thats 480" and you lose about 15% for the metal in the grill so it should be ok. I have a 20X24 filter grill on my 3 ton AC here and it works fine. I use the pleated filters all the time. Dont use the cheap filters and they should be changed every 30 to 90 days . ED

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