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Old 12-25-2010, 11:54 PM   #1
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conditioned crawlspace fan


I have an approx 1800sqft crawlspace that is 18" in height. Next week, I am planning to put a thick vapor barrier on the crawlspace floor and close of all the vents to try to seal off the crawlspace from outside as far as possible.

I am also installing a fan (110 CFM Nutone ultra quiet bathroom fan) on the subfloor to push conditioned air from the living area into the crawlspace (see attached image for location of the fan and the direction in which conditioned air will be pushed into the crawl space. There are enough gaps and small openings in the subfloor so the air from crawlspace will have a return path back to the living area.

What I wondering is:
1) whether, a single fan is sufficient or if I should be installing more fans? (see attached image for location of fan and the direction in which the fan will push conditioned air into the crawlspace)
2) How many hours per day should I be running this fan or should it be running 24x7 ?
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Old 12-26-2010, 01:53 AM   #2
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conditioned crawlspace fan


I'd be worried about condensation forming in the very tight crawl.
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Old 12-26-2010, 04:43 AM   #3
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conditioned crawlspace fan


You should use a supply and return from your furnace to do this. You won't get the full coverage you need the way you are doing it.
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Old 12-26-2010, 10:19 PM   #4
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conditioned crawlspace fan


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Originally Posted by beenthere View Post
You should use a supply and return from your furnace to do this. You won't get the full coverage you need the way you are doing it.
I thought about this a bit. All the ductwork is in the attic, I don't have any duct work in crawlspace. But even if I open a duct into the crawlspace, I won't get full coverage just like the fan. For full coverage (either with the fan or with the furnace) I would need to lay ducts through the length and breadth of the crawlspace? Also, the furnace operates only during the winter, so the crawlspace will remain unconditioned during the rest of the year. I can run the crawlspace fan anytime of the year independent of the furnace.

Last edited by albertpinto; 12-26-2010 at 10:24 PM.
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Old 12-27-2010, 04:46 AM   #5
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conditioned crawlspace fan


Installing a supply at one corner. And a return at an opposite corner. Will get you a full mix in the crawlspace.

In the summer. A few minutes(10 to 14) of blower operation every hour will keep the crawl dry. And bring some of the cooler crawl air into the whole house.

100 CFM of air flowing through the crawl to and from the furnace for 10 minutes. Will exchange 40% of the crawlspaces air.
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