Size of return

Discussion in 'Quotes and Proposals' started by woodbutcher, Oct 16, 2011.

  1. woodbutcher

    woodbutcher Member

    Since I built this house 16 years ago, the geothermal unit has operated inside a closet that allows return air through two louvered grilles that are 10" X 30". The opening in the cabinet that allows airflow over the evaporator coils is 30" X 28". It seems to me that I need one more 10" X 30" opening to feed the proper airflow. The two existing openings are at floor level. Would it be a bad idea to open one on the wall at ceiling level?
    Butch
     
  2. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    Figure a requirement of 6 sq"/1000 btu. So, a 3.5 ton needs about 250 sq".The louvres must be deducted from the free air space so if one had 2 30X10 registers that had a little over 40% free air space it would accomodate 3.5 tons.It is more likely you have something in the neighbor hood of 50 or 60% free air space so you could support a 4 ton or better.
     
  3. woodbutcher

    woodbutcher Member

    Thanks, Joe. That is just the info I need.
    Butch
     
  4. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    A note of caution - I measured a louvered door do an air handler closet awhile back that on the face of it, looked fine, but upon measuring, I learned that the slots were only 1/8" wide per inch of slat...in other words, a free area of just 12.5%.

    There are louvers...and then there are louvers...
     
  5. woodbutcher

    woodbutcher Member

    Thanks, Curt. I measured the louvers. They are 1/2" by 4.5". I estimate 513 sq. in. total.
    Butch
     
  6. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    Sounds good.

    Another quick check is how emphatically the closet door is pulled shut while unit is operating, With proper free area it should merely drift shut. I realize that is not a quantitative test, but it is quick and easy.
     
  7. woodbutcher

    woodbutcher Member

    Yes, the last dealer who came to make an estimate mentioned that the door shuts with more force than it should. I'm looking forward to getting his estimate to see what he recommends to correct that.
    Butch
     

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