return dict size

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  #1  
Old 03-26-05, 02:36 PM
josubway
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return dict size

Last year I bought a resale home in nyc with 1600 square feet which has a 3 ton ac unit with the air handler in attic. The unit works find but we had it checked and the ac contractor who checked it said that we have a 18 inch radius return and that we should have a 22 inch radius return for a 3 ton unit. He stated that it won't cost much to do and and the unit will run better.
Is this right the unit calls for a 22 inch radius return.
 

Last edited by josubway; 03-26-05 at 03:28 PM.
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Old 03-29-05, 05:43 AM
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I would go no less than a 20" round on a 3 ton. 22" would be great. An 18" is more suited for a 2.5 ton unit.
 
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Old 03-29-05, 07:42 AM
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Sorry for the duplicate post.........
 

Last edited by TigerDunes; 03-29-05 at 07:48 AM. Reason: duplicate
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Old 03-29-05, 07:45 AM
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This is interesting question/thread. First of all, what is cost to increase size of the return? How old is existing AC system? When your HVAC dealer says a larger return will work better, what exactly does better mean? Quieter, cleaner air and filtration? Improved operating efficiency? Longer life to system? Do you notice any particular problems with your existing return? How many CFMs do you have in supply and how many do you have in return(I assume this is a central return?)? I think I would want to know a little bit more information especially since you said system was working fine.
 
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Old 03-29-05, 09:33 AM
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Has it been working ok for you? if so Id let it alone. A good job on AC is 60" to 80 " per ton. So a good job at 80sq" per ton for 3 ton is 240sq". Dont have the duct book here. So if my math is right that 18" pipe has 254sq " in it and should handle the 1200 CFM for 3 ton ok.

ED
 
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Old 03-30-05, 06:46 PM
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Radius?

Is this duct actually round (18" Diameter?) or is it 18x8 or 18x10 rectangular? If it is round & 18" diameter, it should be AMPLE for 3 tons. Of what material is the duct made? Even if it were flex it should be fine, presuming round duct.
 
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Old 04-01-05, 06:54 AM
Thomas W.
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return duct

It neve rhurts to increase within limits, I would not increase that return aI would add a small plenum( duct box) behind if horizontal or next to if vertical and add a new return to a roon you have that may be a littl eto warm in the summer. They can runh a 10" with a 12"X12" return air grill.

This will help with your overall air circulation throughout the house also.
 
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Old 04-02-05, 05:38 AM
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Help me out here please.

When you size a duct system do you size on a friction method or a pressure method.

In Man. D the system that is explained the most is a friction method.

Using that method there are too many variables that a duct system can have to say that a 18" 20" 22" return is approiate.

How long is the return What kind of fittings are in that run.
What size is the supply duct, Fittings and all.
What size is the blower and what amount of air will it blow under certain conditions.

With all that said I could not tell someone that there return is too big or too small.
Get a second opinion from another contractor.
 
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