We live in the desert where it's quite hot. We have a 2 story with central a/c with seperate units for bottom and top floors. While the a/c was off i noticed what felt like hot air from the second floor a/c intake. I went into the attic where i could look down between the walls and saw that the intake, which I suppose is supposed to fit up agains the wall, has about a 5" gap around it that exposes it to air in the attic, which is quite hot.

You can see in the pictures the gap between the intake and the wall. One picture is taken from the attic looking down on the intake from the wall where you can see the gap. The other is

This doens't seem right to me, as my assumption is that the intake is pulling in hot air from the attic which is making it difficult to cool the recirculated air. I was thinking of purchasing large chunks of foam insulation to fill the gap between the wall and the intake. I figured I should get advise before I do this though, because a lot of a/c issues aren't always intuitive to me. So, is there any reason that this gap is supposed to be there? Would it probably we helpful if filled in the gap?

I also noticed that for this same unit there's an intake in the unfinished garage, but with no output vent into the garage. You can see that in the bottom picture. The previous owner of the house covered it with a piece of cardboard as you can see from the picture. Is there a reason the origional a/c installer would put an intake into a hot garage, especially considering there is no a/c vent into the same garage?

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    Not fully sure I follow both intakes but they could have been intentional, make up air vents in some cases depend on the sealing and conditions, I have helped in desert but not been the design person. Normally I believe the make up air vents are smaller but that depends on the size of the system and if more fan time at night time is used to cool the structure , Hope this helps as I have limited experience but I do know night verse day makeup vents make a difference.
    – Ed Beal
    Aug 17, 2020 at 0:25
  • I just spent some time looking up "make up air". It looks like that's to balnce pressure for other house exhaust systems. In this case it's air routed directly into that A/C intake, which doen't seem it would make sense.
    – Frank
    Aug 17, 2020 at 14:30
  • The air going into the intake conditions the air and provides the home with a slight positive pressure, pushing out bathroom and kitchen vents Along with any areas that are not sealed by adding fresh air this helps to maintain a healthy air mix getting rid of excess Co2.
    – Ed Beal
    Aug 17, 2020 at 16:50
  • I should have mention that you also need fresh air because TV Jesé are open air combustion normally one close to the ceiling and one close to the floor if I remember correctly this helps to mix the air so there could be 2 reasons.
    – Ed Beal
    Aug 17, 2020 at 17:41


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