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Where to place returns?

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  • Where to place returns?

    My son's new house has upstairs heated and cooled by attic unit (gas hot air).
    All supply ducts run to ceiling registers; no returns in any room (6 if my memory is right).

    Only return is in the central hall 16" x 32" that is directly below unit in attic via duct board box. York unit has 75K btu input on it.

    He wants to install returns for each room because they get little heat in the room with door closed to the hall but we are confused about best way to arrange ducting for return:

    Return in ceiling about 10' away from supply registers. Concern: Does the air (especially in winter during heating) just exit the supply and run along the ceiling and exit via the return and not "mix" with rest of room's air?


    Cut a hole in both sides of wall communicates with the central hall and place a register on both sides to let room air be sucked by return in ceiling of central hall. Concern: Loss of privacy with anyone in hall hearing any sounds from bedroom?

    If you suggest ceiling as best way, how critical is sizing of the return duct (round)? If room supplied by say a 6" round, would a 6" round be best for return or does size have to up or down vs supply dimension?

    If wall, again, how large a hole/grill size to cut for?

    Any other suggestions/thoughts?

    Thanks in advance!

  • #2
    cut an 1" inche off the door bottom, 1 inch off would be 30 square inches, (on a 30 wide door), 6" round duct would be about 28 square inches,

    that way you would maintain the cross flow, from ceiling to floor,
    Push sticks/blocks Save Fingers
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    • #3
      Seems the wife has already down voted that concept.


      • #4
        BHD's suggestion is the best, and almost free/no cost. Be careful cutting the doors, use a good quality fine tooth blade and provide edge protection to prevent splintering and you should be in good shape.

        What is here objection to trimming the bottom of the door? It might not be necessary to cut a full inch off, maybe 3/4 or 1/2 would work. Start with the least cut and if you have to trim it some more.

        In fact, why not trim a half inch from one door only then compare the difference to the other rooms. I bet she would never notice a 1/2" if she didn't know you cut it.
        "It's a table saw, do you know where your fingers are?" Bob D. 2006



        • #5
          Unless you plan to design a zoned system, placing returns in the room means you will lose control of the room temperature. Since the air is being returned before being sampled by the thermostat, you will not be able to set the room temp.

          So unless you plan to upgrade the system to a zoned system I would suggest keeping the return in the hall.

          So the trick is to get airflow with the doors closed. I would not suggest undercutting the door - apart from the looks the opening will be way to restrictive to allow the correct airflow. Due to the narrow opening and the air being sucked in from different directions there will be turbulence and other effects which will impede airflow. Simply matching theoretical areas does not work. the amount of undercutting needed to get correct airflow will make it unacceptable.

          There are special grilles sold for returning air from rooms to the hallway called transfer grilles. They have the necessary design to ensure proper airflow and v-shaped louvers to help maintain privacy. They are typically installed at the boom of the door. However there will be some loss of privacy as far as noise propagation once they are installed.

          I would suggest either fitting appropriately sized transfer grilles or installed a zoned system with thermostats in each room.
          Last edited by blue_can; 03-14-2019, 02:21 PM.


          • #6
            Thank you Bluecan!


            • #7
              Why not cut 1 Inch of of the TOP of the Door ???
              I can build anything You want , if you draw a picture of it , on the back of a big enough check .


              • #8
                Yes, I agree to the comments above.