• In this video, This Old House plumbing and heating contractor Richard Trethewey explains how to retrofit central air conditioning.


    1 Air is drawn in through a single return duct.
    2 The air is then pulled into the air handler mounted in the attic where it’s cooled.
    3 A main supply trunk of larger ducts connects to the air handler.
    4 Cooled air passes from the supply trunk to small-diameter ducts throughout the attic.
    5 Each small duct is attached to a round outlet that’s cut into the ceiling of each room.
    6 The outlets are placed in the corner of the ceiling to avoid blowing cool air directly onto people in the room.
    See products and services from this episode.
    • 2 to 4 days, depending on size of house and number of rooms
    • Difficulty: Hard
      System must be installed by a licensed heating and cooling professional

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      1. Mini-duct air conditioning system