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Small Cabin Forum / Cabin Construction / Window unit didn’t work as well as I’d hoped
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mattd
Member
# Posted: 9 Jul 2018 21:46 - Edited by: mattd
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Got my cabin wired to run off gen. It’s 300sg ft and I was running a 6000btu window unit.....from 1993.

It was a very mild day, low to mid 80s, but my cabin bakes in the sun for a few hours. Also it’s a gambrel roof, and is essentially 2 open stories. Walls are insulated, ceiling is not.

Started the ac when outside temp was 76. It blows cold air. After a few hours outside was 80 inside was 78. Which I would say is typical without the ac...it warms slower then outside.

I turned on the ceiling fan to see if that would help. It didn’t, just brought the hot air down, so stopped it after awhile.

During this time the ac was blowing cold, but not as cold as earlier. Later in the evening, when temp was much lower, it was blowing really cold air. All this time though it never dripped any water out of the back.

All in all it seems like the inside air followed a typical path through the day, with the ac making very little if any diff. So, is 6000btu (rated at 250sgft) just too small to do anything w 300sgft? Is it too old and not functioning at full capacity? Or will an uninsulated ceiling defeat any ac unit?

Hesitant to replace w larger cause I know this size runs off my Inventor gen. Although it’s so old a new, larger one would proly be more efficient.

ICC
Member
# Posted: 9 Jul 2018 23:50
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Quoting: mattd
Walls are insulated, ceiling is not


That is a big part of the problem.

DaveBell
Member
# Posted: 10 Jul 2018 00:49
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Quoting: mattd
Or will an uninsulated ceiling defeat any ac unit?

You have a battle between the attic oven and the A/C unit. Insulate the ceiling and make sure that oven above your head has passive ventilation.

https://www.energystar.gov/index.cfm?c=home_sealing.hm_improvement_insulation_table

Nate R
Member
# Posted: 10 Jul 2018 08:00
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Uninsulated, open like that, yeah, 6K BTU isn't going to do it. And even still, hard to say if that 1993 is putting out full BTUs. A more modern 6K BTU unit will likely be more efficient. Is there a wattage published on your unit?

Either go bigger or insulate the ceiling, I think.

sparky30_06
Member
# Posted: 10 Jul 2018 08:41
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I have a 14,000 BTU portable in my 200 sq ft cabin in south Texas. My roof is only 2x6 with insulation but the floor is insulated and it can't keep up in the heat of the day. I have a feeling that the ratings on window and portable units are not as advertised.

ICC
Member
# Posted: 10 Jul 2018 09:06
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Re, portable A/C units. Many of them have a handicap, only an exhaust hose; no inlet hose. The best ones have two hoses. With a single hose, hot outside air has to leak into the cabin to replace the air that is exhausted. So those don't work as well as the btu rating might suggest.

ICC
Member
# Posted: 10 Jul 2018 09:43
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https://learn.compactappliance.com/dual-hose-vs-single-hose/

Eddy G
Member
# Posted: 10 Jul 2018 09:48
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Personally, I think unless you insulate the cabin you'd be better off with an exhaust fan. It would pull some fresh air through the cabin. Air flow will bring some comfort.
Trying to run a/c in an insulated hot box is like trying to cool the outside...doubtful the compressor is ever going to stop running and run itself in to the ground...

Borrego
Member
# Posted: 10 Jul 2018 10:18
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Quoting: mattd
Is it too old and not functioning at full capacity? Or will an uninsulated ceiling defeat any ac unit?


Yes
Yes

Cowracer
Member
# Posted: 10 Jul 2018 12:24
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My cabin is 576 sq feet on two distinct floors 256 on the bottom floor (16x16) and 320 on top floor (16x20). I have 2 11k btu window units, one on each floor, and my cabin is well insulated. I can keep in any temp I want, on any day.

There is NO WAY a 6k unit is gonna do anything for a 300SqFt un-insulated space. Sorry, you are gaining more heat in the sun than you can pump out with the A/C. Actually, even well and fully insulated, you are on the low side of capacity for that space. TWO 6k's would keep up, but not even then unless you insulate.

Tim

Cowracer
Member
# Posted: 10 Jul 2018 12:32
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Funny story on a related subject...

Have a good friend that built a 3 car garage. He was going to host a "garage warming" party in it. He get a HUGE 240volt window unit for the garage. This monster was probably 25 or 30K btu. The garage is insulated and shaded. I told him it ought to make it 'reasonably' cool. He gets it all set up the day before and he calls me that he has run it all day and it'd just as hot inside the garage as outside. I'm like is it blowing cold and he says yeah, but it's not 'cooling' of the garage.

I agree to head over and take a look at it, and when I walked in, I saw the monster window unit, sitting on a 55 gallon barrel in the middle of the garage, merrily chugging away on full blast.

"Dave... Ya gotta point the ass end out the window"

"huh?"

"Dave, can't you feel all the heat coming off the back end of this thing? that needs to go outside."

"Oh hell, No one told me that!"



Tim

ICC
Member
# Posted: 10 Jul 2018 16:50
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He was heating the garage. Amazing what some people do.

DaveBell
Member
# Posted: 11 Jul 2018 14:10
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Quoting: Cowracer
Funny story on a related subject...


From the Department of Redneck Engineering:

Redneck Heatpump..

In the summer, Elmer mounts his AC window unit cool side in to cool his cabin and then in the fall, Elmer mounts the AC window unit cool side out to heat his cabin.


creeky
Member
# Posted: 12 Jul 2018 16:35
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I put a sunsail up overtop of my studio. ITs insulated but that attic still heats up pretty good. the sunsail makes a lot of difference. a small 5k btu a/c unit works fine.

sparky30_06
Member
# Posted: 13 Jul 2018 10:02
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Quoting: creeky
I put a sunsail up overtop of my studio. ITs insulated but that attic still heats up pretty good. the sunsail makes a lot of difference. a small 5k btu a/c unit works fine.


That gives me an idea. Little bit of sun shade fabric from a greenhouse, attached to a frame work over the roof. Wonder how much thermal gain i could get rid of

Eddy G
Member
# Posted: 13 Jul 2018 11:19
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A lot of one we don't get at our cabin is Sun. We are heavily shaded. Good for summer but not so much in the winter. Snow tends to build up and melt off a lot slower..

Eddy G
Member
# Posted: 13 Jul 2018 11:25
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Quoting: Cowracer
Cowracer
Member # Posted: 10 Jul 2018 12:32
Reply Quote

Funny story on a related subject...

Have a good friend that built a 3 car garage. He was going to host a "garage warming" party in it. He get a HUGE 240volt window unit for the garage. This monster was probably 25 or 30K btu. The garage is insulated and shaded. I told him it ought to make it 'reasonably' cool. He gets it all set up the day before and he calls me that he has run it all day and it'd just as hot inside the garage as outside. I'm like is it blowing cold and he says yeah, but it's not 'cooling' of the garage.

I agree to head over and take a look at it, and when I walked in, I saw the monster window unit, sitting on a 55 gallon barrel in the middle of the garage, merrily chugging away on full blast.

"Dave... Ya gotta point the ass end out the window"

"huh?"

"Dave, can't you feel all the heat coming off the back end of this thing? that needs to go outside."

"Oh hell, No one told me that!"



Tim



I've been in the HVAC climate control biz 40 yrs and just about nothing surprises me any more...I can't count how many times I've seen or heard things like that....lol

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