I'm remodeling and placing a new HVAC unit in the attic. The dining room is central on the house, adjoined by the living room, kitchen, service bathroom, and (directly or via a hall) all three bedrooms.

The unit is 3 ton, and the house is 1200 square feet.

Also, the dining room will have a tray ceiling notched up 12". The tray will be about 11' by 11', and the dining room 14' x 14'. The intake will be in the upper section, so 9' above the dining room floor.

I want to stop "backwash" of air directly from the outlet vents (esp. in the dining room and kitchen) to the intake. So far I'm intending to keep them as far apart as possible, and also point the vanes slightly away from the intake, but are there any other good options available?

Also, I'm mainly concerned about efficient AC more than heat. This is central Texas.

  • Three tons (36 kBTU/h) in central Texas should be more than enough to cool 1200 sq ft in a compact layout with return ducts in central Texas I am assuming you have good insulation in the attic. Our 2000 sq ft tract house in a compact layout in north central Texas has no return ducts and is barely cooled by a 42 kBTU/h a/c condensing unit. Nov 23, 2018 at 20:45
  • I am actually more interested in knowing what minimum spaces are/should be between outlet and inlet, etc.. Nov 23, 2018 at 22:05
  • re separation: none is suffici9ent more is better
    – Jasen
    Nov 23, 2018 at 22:56

1 Answer 1


Here is a piece of the puzzle you may not have considered. In air conditioning mode: The cooled air being expelled from the supply registers is far heavier than the room air being drawn into the return air. As air is cooled be the A/C unit it condenses dramatically. This cooler, heavier air will drop right to the floor and push the warmer room air up and into the return. The warmer lighter air will gravitate to the highest point in the room. You have little or no concern of the conditioned air being drawn directly back into the return air. Good Luck.

  • I actually had thought of this, but also wanted to get feedback from others (like this also). Of course the converse with heating has challenges; if I could swing it I would attempt to bifurcate the intake and have an alternate route near the floor for heating. Thoughts on that? Nov 26, 2018 at 13:27
  • My contention has always been that we should heat from below, (warm air rises) and cool from above (cooler air falls). In the higher end homes we see this strategy employed more. Many folks don'
    – Paul Logan
    Nov 27, 2018 at 5:04

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