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In winter we shut the vents and turn off fan of crawl space so not heating more of the outdoors- insulating air/ground keeps us warm. Former owner said to open vents and run fan all summer, but it seems that blowing 90 degr air through crawl space when running AC to get to 80 degr right above crawl space is dumb- that cooling that air over and over again has to cost more than chillling it and leaving it chilled and stagnant. Unlike my attic fan, which is set to run at 70 degr and up and so runs almost 24/7 for a few months and cools house by dropping attic from 200 degr to 100 degr, I would like a negative setting for my crawl space fan to only turn on if the temp is BELOW 80 or maybe 75 (happens most nights for a few hours).

Any thoughts on the rationale for doing this or not, and is there a way to get it to turn on when it gets cold? BTW while I make DH shut garage (next to crawl space and also under house proper) in winter to save on heating costs don't yet agree that we have to shut garage in summer to save on cooling- would probably make garage unbearable to enter when necessary..

(BTW I DO turn on the crawl space fan when the house gets whiffs of chicken coop mildew- usually after heavy rains.)
 

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I keep our vents open and a fan running so that i won't have that musty smell. our furnace and ac seer is in our crawl space (6ft tall) so there is always a little moisture in our sump pump from the ac. we also use ours for storage so i want it as dry as possible.
 

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An unventilated crawl space will breed mold, and you don't want that. It won't just keep to your crawl space once it gets going.

Our fan is on a humidistat, so only blows when the humidity gets above whatever my dh sets it at. Seems to work fine.
 

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SO I should even run it in winter.....
 

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Id just leave the vents open and not run the fan as long as youre not having moisture problems. And your duct work should be insulated so there shouldnt be a lot ot heat exchange anyway
 

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Hi,
Here is a link you might find helpful:
http://www.advancedenergy.org/buildings/knowledge_library/crawl_spaces/

A lot of people are now going with a "conditioned" crawl space.
With this approach, you put poly with edges and seams sealed down on the dirt -- this eliminates the main source of crawl space moisture. Then you insulate the walls and rim joist. Then seal up the vents and keep them sealed all year.

I don't have any experience with this in humid climates, but some of the studies indicate that this approach does better both summer and winter, even in humid climates.

Gary
 

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Originally I had my crawl space vented. I didn't see the advantage of having hot humid air down there. I decided to treat it like a basement (there has always been a moisture barrier on the ground). I sealed up the vents and insulated the walls and rim joists.

It now stays about 66 degrees down there and the humidity runs about 50%, as opposed to 90 degrees and 85% humidity outside. The house is much easier to cool and has less humidity than before. No sign of any mold or mildew.

I did put an indoor/outdoor thermometer with humidity sensor (under $20) in the laundry room. I drilled a hole in the floor and put the remote sensor in the crawl space. This way I can monitor it with no effort!

Kathie
 

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It's important to the wood foundation structure of any home to avoid collecting moisture in the crawl space(raised foundation). This threat is doubled in the hot, humid Souith. I was shocked when I appraised a block & sill frame home that had been "improved" by bricking up to window level all around without vents. The yellow pine floor joists were coated with a pale powder and offered little resistance to inserting a knife blade. Was found to be beyond reasonable cost to repair and torn down. I would check with an expert about moisture barrier/insulation under the floor to reduce infiltration. Might be cheap for the money. Good luck to you..Glen
 
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