return vents

buggghead

im fixing a bad return install. unit is a 3 ton goodman hp package unit. it had one return that was undersized. i ran returns in everyroom. floor return grills running through floor jouses (paned). to duct that leads back to unit (straight). i have 6x12's in every bedroom (4 total) then a 6x24 in livingroom (double paned). do you think i need more vents than this. or th even use a larger regester

buggghead

forgot to state my supply duct is supplying to the house 1350 cfms of air.

HVACDave

So, you will end up with 3 sq. ft. of return grate area with a 3 ton system. Rule of thumb is 400 cfm/ton AC so you will have approx. 1200 cfm going through 3 sq. ft. which makes a face velocity of approx. 400 feet per minute (fpm) without accounting for grille construction which will further reduce your open area. Standard recommended face velocity for return grilles is 400 fpm max. so you may want to increase grille size a bit to be below that.

Just saw your second post, you will need to add one more return, or make them bigger to stay at less than 400 fpm with 1350 cfm.

REP

The sizes you have chosen kinda surprises me.If you have 16" on center stud spacing ,then 14x6 and 30x6 are made to take advantage of the availiable spacing.Its very hard to have too much return so why not use the larger grilles?

alecmcmahon

check out this link, I found it helpful when doing my system.

http://www.google.com/url?sa=t&rct=j...x2-lISZXDgXEQQ

beenthere

Did you actually measure that amount of air, or are you guessing that amount base off of something.

If you have a VS blower, and have the blower jump set for 1320 CFM, you probably still aren't getting that much air.

Your 6X24 should be atleast a 12X24.