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Old 07-11-14, 01:57 PM   #1
gasstingy
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Default 12v DC Foundation Vent Fans

Has anyone made a 12v solar power ventilation system for the crawl space under their house? I’ve looked through quite a few pages of projects here going back several years and came up blank. Regardless, solar powered crawl space ventilation seems like a marriage made in heaven, so to speak.

Here’s the idea. I’d buy 8 12v computer style fans, wire them up with an inline blade style fuse going to each fan. Total up the power required to run them (12V * 0.60A) = 7.2w, 7.2w * 8 = 57.6W for the eight fans. Then I’d buy a solar panel that is rated about 80W. This way the fans would run wide open in bright sunlight and the power would fall off in lower light, and then not operate at all at night. If a humidistat could somehow be inserted into this plan, I’d love to put one in with a couple sensors to increase my odds of dehumidifying the crawl space as much as possible. I’d need your help with the humidistat setup. The power figures for the fans came straight off the back of the fans we buy/use to cool our LED price signs. I can get them at out cost of ~ $16.50 / each. They are rated at 120 cfm, so 8 should work out to 960 cfm once in a while.

I’d like to know about it if anyone has done anything like this, whether it worked well or not. I have a full vapor barrier under the house and it helps some. But, I still need to make it less humid. This was the idea that popped into mind.

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Old 07-12-14, 09:28 AM   #2
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You could have a car battery on the panel and put the fans on a timer.
I say timer so you can control the vent times to turn on after the dewy mornings and end shortly after dusk, to vent the warm day air that contains the higher moisture, once it cools.

I found from my last houses garage that the sunlight warmed the garage till the night air would cool and condense moisture in the warm garages air, leading to mildew/mold.
I put a vent in so it naturally convected and that solved the heat build up with moist air issue, perhaps you could make a side vent chimney to encourage ventilation.

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Old 07-12-14, 05:07 PM   #3
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The two questions you need to ask are what is the coldest surface temperatures in the crawlspace and what is the dew point of the air?

These are important questions because most of the time adding ventilation to a crawlspace is actually adding moisture rather than removing it from the space. I thought Alabama was one of the hot moist states, if that's true, this is a bad idea.
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Old 07-14-14, 01:00 PM   #4
gasstingy
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Thank you both for your responses. I only use the internet at work during my break times, thus the delay responding.

ecomodded: You are closely describing the setup I used to have under the house. I had a very low amp draw squirrel cage fan plugged into a lamp timer and ducted it to the outside. It was set to run about 4 hours a day, midday. Of course, the downside was it was rain or shine. Still, it was slightly less humid under the house with that. I looked for a humidistat at Lowes this weekend and came up empty handed. With a humidistat, it might work a bit more effectively.

MN Renovation: You are absolutely correct with Alabama being one of the hot moist states. I suspect the coldest part of the crawl space would be the plastic ground cover. It is what is covered in condensation and worrying me. Any suggestions on a better plan? I am trying to remain open minded as I am quite aware that I am far from knowing everything. I am really trying hard not to go to the expense of sealing the space up and running a dehumidifier under there. If I read about dehumidifiers correctly, they are something of an energy hog.

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