Cooling attic with window a/c in wall vs window

Discussion in 'Do It Yourself' started by bigslick7878, Oct 11, 2014.

  1. Ok so I am forced to grow in attic, and while I need to keep a/c running I cant do it as weather gets colder. I mean it is 60 outside and I have 2 a/c running doesnt look quite right.
    Attic has walls blocking off two crawl spaces on sides, with pretty big pockets (about 500 cubic ft) on either side. (See diagram)

    Could I take the window units out of the window, and install them in so front side is on grow room side wall, while back of the a/c filters to the crawl space behind?

    Only thing I am worried about would be heat building up on back side, but don't they get that hot in middle of summer when it is 100 and back of a/c is hanging out window?

    I will have 2 6 inch fams pulling heat out if the compartments thru the soffit, so does anyone see why this wouldn't work?

    Just can't have these things in my windows anymore, and don't see point of spending big mobey on portable system if I have prefectly fine window ones I can stick inside.

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  2. image.jpg image.jpg This might help. I use an inline duct fan to draw the heat out.
  3. Excellent. Thanks. What is that a sheet metal box you built on the back?

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  4. Ok so I just got a lesson on just how much heat comes out the back of a 15,000 BTU window unit. It is a MASSIVE amount. More than I could have ever imagined. I cut a hole in my flower room wall, had it venting into the attic crawl space (which really isn't that small, prob 500 cubic ft) and everything was fine for about an hour. After the heat built up, compressor was obviously heating up and being overworked and 20 amp breaker kept blowing.

    Tried numerous quick fixes trying to draw the hot air away from back of unit, but nothing could keep it going for more than 2 hrs. I woke up the next day to 107 in the room!

    So I built a box and exhaust system for back. Had an extra 250cfm 6in fan laying around, used that and return box and this is what I came up with. I plan on venting it through the floor and into a drop ceiling space directly below attic. Of course there is a stud right where I am trying to vent in crawl space, so I have to work on that later to get it all hooked up.

    I was stunned when I crawled behind there when it was running and felt that heat holy sheet it was crazy!! But then it made sense why fuse kept blowing. I hope the 6 inch is enough, if not I can just switch it with a higher power fan and/or add another exhaust to back side of box.

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  5. Just a heads up, the heat coming out of the AC will be warm moist air. Will fog everything right up and potentially create mold if vented inside the space.

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  6. Venting it through the floor into drop ceiling, and into lower floor room below when it gets colder.(which will be soon)

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  7. Well I am at a loss. Keep blowing a 20 amp fuse, even with the exhaust hooked up and blowing through the floor into room below. I mean piping hot air is coming out of that thing when the compressor is running.

    Had it on 75 economy mode, lasted an hour.

    Bumped it up to 80, econ mode low fan speed lasted 2 hours. Tried pushing it (lol) to 77, went out within half hour. Have it back at 80 and just praying it stays on, I have been trying to get this right for a damn week now.

    I just don't get it. The box on the back is about 1.5 cubic ft, and I have a 250cfm fan pulling the air out so how the hell is it overheating?? The a/c only pulls 12 amps, I have it on the power saver setting, 77, AND low fan speed and it blows the fing breaker.

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  8. #8 Halo-noob, Oct 23, 2014
    Last edited by a moderator: Oct 23, 2014
    Venting two 5kw Ac is a big task. The condenser on those probably runs a 10-12" fan. Just a note,running the fan slower also runs the condenser fan slower. Window style AC units are already and running at the MAXIMUM on a hot day. Any restrictions at all on the condenser will kill it. You will need lots more airflow.

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    Edit. 10kw of heat will heat a whole 3-4 bed house on a cold night.
  9. I think I might have found the issue, I got in back and checked if any heat was building up back there and saw the tape on the bottom had come loose and warm air was spilling out into the area again. So I got some thick aluminum tape and sealed it up good, no leaks now.

    I have read that whatever size the exhaust fan is inside the unit is what size the one on the box should be. I cant see inside, but looked at a tiny 6000BTU unit I have and it looks like that is running a 6 inch. Obviously the 15k BTU is gonna be running a larger one.

    I ran it all last night set to 78 now with no issues after I fixed the leaks. I am going to keep dropping it by a degree every night and see how far I can push it with current set up/ weather outside. (Lows around 50 at night, highs of about 65 during day)

    Good chance I will have to add another fan though when it gets warm in spring again. Weather should be in my favor moving forward over next 4-5 months or so.

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  10. Also that much heat will make you roof glow under FLIR

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  11. LOL I feel like such a dumbass. Blew again last night, was pissed off until I was the surge protector tripping..not the fusebox! Direct line to the outlet now, running at 75 on high issues.

    Unreal. I kept wondering why I never saw the fuse actually tripped on the box, and that is why. You know how sometimes it can trip but wont flip over so you can't tell? I thought that was happening. Wrong.

    I can sleep now.

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