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Author Topic: Roof vents open or closed with AC to cool unit?  (Read 3715 times)

repcool

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Roof vents open or closed with AC to cool unit?
« on: June 25, 2010, 09:05:57 PM »
My wife and I are in an argument.  Is it more efficient to keep a 5er cooled by AC with the roof vents open or closed?  My theory is that the hotter air will always go up and can leave via the vents.....she ain't buying it.  Any thoughts?

Simon
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SargeW

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Re: Roof vents open or closed with AC to cool unit?
« Reply #1 on: June 25, 2010, 09:24:20 PM »
For my 2 cents you are both right.  I usually open the vents for the first few minutes to vent the heat, then close them up to keep in the cool. I would also recommend covering the vent in really hot weather if the sun is shining on the vent with a vent cushion or something similar. There isn't too much of an R factor in that 1/8 inch plastic dome to keep out radiant heat.

Sarge
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demingrick

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Re: Roof vents open or closed with AC to cool unit?
« Reply #2 on: June 25, 2010, 09:24:41 PM »
Hot air does rise, but hot air will also come in through a open vent. I leave mine closed when the A/C is on.
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Re: Roof vents open or closed with AC to cool unit?
« Reply #3 on: June 26, 2010, 07:09:51 AM »
There may be some advantage to opening vents and even windows when it is initially very hot inside, but once the temperature comes down a bit, everything should be closed up.  More heat comes in than goes out. Those vents are a major source of heat gain (and loss on cold days), even when closed. Get those 14x14 insulating pillows to stick in there for those very hot days and cold nights - it helps a lot.
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ttyR2

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Re: Roof vents open or closed with AC to cool unit?
« Reply #4 on: June 26, 2010, 01:54:34 PM »
Any breeze can also force hot and cold air in and out of vents. Technically in absolutely calm weather, heat should only rise up out of the vents, but it doesn't take much of a breeze to blow hot air back in.
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carson

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Re: Roof vents open or closed with AC to cool unit?
« Reply #5 on: June 26, 2010, 02:11:20 PM »
Good grief, but technically correct. When the wind blows, close the vent; if not....


carson Fl 96.6 and no wind.


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tvman44

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Re: Roof vents open or closed with AC to cool unit?
« Reply #6 on: June 26, 2010, 02:34:47 PM »
I leave mine open all the time, winter and summer.

ArdraF

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Re: Roof vents open or closed with AC to cool unit?
« Reply #7 on: June 26, 2010, 08:51:52 PM »
Quote
I leave mine open all the time, winter and summer.

Why?  What do you gain?  I should think you use a lot more heating and cooling than those of us who leave our vents closed.  Or, do you not use A/C?

By the way, we open one and use the fan when we turn on the propane range or oven - primarily to get out fumes.

ArdraF
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silveradomike

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Re: Roof vents open or closed with AC to cool unit?
« Reply #8 on: June 28, 2010, 01:12:36 PM »
Do you also leave your widows open when you use your TV air?
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repcool

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Re: Roof vents open or closed with AC to cool unit?
« Reply #9 on: June 28, 2010, 08:41:10 PM »
Some good debate here....I went ahead and ordered some insulation pads for the vents.  Thanks!
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DesertDew

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Re: Roof vents open or closed with AC to cool unit?
« Reply #10 on: June 28, 2010, 10:26:55 PM »
Living in the very hot desert of the southwest, closing up everything once a place begins to cool down is standard.  Somewhat like a car a/c when the car is 160 degrees inside...when the car interior is very hot, initially it helps to have a window open (since the outside air is a bit cooler) allowing the hottest air to escape, then close the windows as the cool air cools down the interior to a temp cooler than the outside air.  If there's any breeze at all with a rv vent open, my experience has been that it will overcome the power of hot air rising out the vent and allow hot air in. 

Sarguy

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Re: Roof vents open or closed with AC to cool unit?
« Reply #11 on: June 29, 2010, 01:31:42 PM »
I know you should always vent when running heat (carbonmonoxide?).  I take it there is no problem totally closing up with the A/C running? How far away should the portable generator be from the RV on a windless day? I hope I didn't go too far off subject, these posts just raised more questions for me.
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carson

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Re: Roof vents open or closed with AC to cool unit?
« Reply #12 on: June 29, 2010, 01:37:29 PM »
  When running the A/C on a normal motor home, there will be no air "sucked" into the RV. It always recycles internal air. The only exception is when you run the engine/dash A/C in the vent position.

Carson
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Bob Buchanan

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Re: Roof vents open or closed with AC to cool unit?
« Reply #13 on: June 29, 2010, 06:23:21 PM »
Some good debate here....I went ahead and ordered some insulation pads for the vents.  Thanks!

Air is sucked into an air conditioner, cooled, and then forced back out. If a vent is open, it sucks that air in as well -- so if you leave the vents open, you are now cooling the world . . .  8)

This is not really debatable, IMHO . . .

Yes, seal every possible vent, crack, hole, or wherever else outside air might be sucked in. For everyone you miss, the efficiency of your AC will be decreased.
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