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  1. #1
    Join Date
    Jan 2010
    Denver CO

    Return air sizing

    This may be impossible to answer without a visit but a general answer would be great.

    House: 2400 sq ft, two story with unfinished basement. First floor has 9ft ceilings and one vaulted ceiling going to the second floor. Furnace is in the basement. Rheem Critirion model RPGJ-12EARJR. Thermostat is Honywell CT3500/3595 (that's what the manual says).

    House has a total of 4 return air grills. All are 29" x 5" with return air going through the empty spaces between studs. 1 return is at floor level of main floor. 2nd is at ceiling level of 1st floor. 3rd is half way up the stairs. 4th is at ceiling level of 2nd floor in the hallway. This last return goes down the hallway wall then across the garage (unheated garage) ceiling and down the garage wall to the basement. I used this return to run internet to the second floor and found the return filled with insulation where it goes horizontal across the garage ceiling.

    There are no return air grills in any of the 4 bedrooms.

    Is that sufficient return air? I would have thought there would be returns in the bedrooms.

    While sitting here this morning I've noticed that the furnace cycles on for ~10 minutes then cycles off for ~1 minute then back on again (not sure if this has anything to do with return air).



  2. #2
    Join Date
    Sep 2005
    those returns are probably good for 225 to maybe 250 cfms each.

  3. #3
    Join Date
    Oct 2008
    You might want to think about add some kind of transfer grills in the bedrooms,without ugly vents above the doors, check the location of your thermostat, and adjust your heat anticipator for proper cycling.. Technically the better the air flow the more eff. the equipment will be with the exception of having the return right next to the supply..
    "Rock-n-Roll " Ain't noise pollution..

  4. #4
    Join Date
    Aug 2002
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Likely undersized returns,call around and ask "Can you test the static of my duct system,supply and return?.

    Keep dialing until you get a yes.

    You need a Pro.

    If you post pics of the indoor unit and connecting ducts,plus sizes of duct going to the returns,we may be able to tell you more.

    Transfer grilles ,as stated above may help,but likely need more then that.

  5. #5
    Join Date
    Jan 2010
    North Huntingdon,Pa
    leave bedroom doors open for 1

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