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Newbie: Need Advice on Durable/Wet/Dry Fan for under house....$900 estimate?

Newbie: Need Advice on Durable/Wet/Dry Fan for under house....$900 estimate?


Old 01-07-05, 07:00 AM
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Newbie: Need Advice on Durable/Wet/Dry Fan for under house....$900 estimate?

I have a 1939 home in Tampa, FL did an addition 5 years ago. My house went from 1300 S.F. to 2300 S.F. The home is on approx 1-2 piers and is a wood frame house. In the addition, I placed hardwood floors and there is insulation underneath the floors.

Recently, I had an engineer over at the house who took a look underneath and said that the area under the addition has no circulation.

He estimated that we need an electrical company to run electricity under the house that is completely insulated and install some fan that can handle getting wet which alone costs $400-$500.

So, the total with his labor, electrician, etc... = $900.

He said that not anybody can do this job because it is a liablility to run the electrical under a house next to insulation and risk water exposure.

So, unless it is done properly, it is a fire hazard/risk.

So, anybody have some advice, suggestions?

$900 seems very very high.


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Old 01-07-05, 07:37 AM
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How high is the crawl space? How wet does it actually get in there? Did you consider just adding vents on the walls? That's usually enough. Running the electricity is not a problem, if they consider that bad how about running wire underground? That defintely gets wet.
Old 01-07-05, 08:08 AM
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This isn't really electrical advise, and I have no specific knowledge of Florida conditions, but I think the first priority is to make sure that all the dirt in the crawl space is covered with plastic sheeting.

I hope the hardwood installers put a vapor barrier under the hardwood (usually roofing felt, but maybe something different in Florida).
Old 01-07-05, 08:40 AM
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Here's the best solution to your problem (with a little background). Been there. Done that.
Built home with 4' crawlspace, insulated floor, normal venting, standard switched lights circuit, and a regular 3-prong power outlet receptacle under there (20 amp breaker, 12/2-with-ground wire). I do all of my own electrical and plumbing so I just light the whole crawlspace up with the flip of a switch at the crawlspace door, and the outlet is under there for my yard water well pump, power equipment, etc.
I live on Albemarle Sound in coastal NC, which I'm sure has comparable humidity (very high air and ground moisture). I had a contractor that I trust look at a similar wet crawlspace problem (dripping pipes, ductwork, insulation, etc.) years ago. I was going to pay him to install a ground vapor barrier.
He advised me that because the air humidity is so high here that it really wouldn't solve the problem (no vapor barrier, no charge).
He just advised me to increase the air circulation under there. Determine your cubic footage of crawlspace (length X width X height from ground to bottom of subfloor).
I contacted W.W. Grainger (1-888-361-8649, 7a-7p, M-F. CT) and spoke with Tech Support there. www.wwgrainger.com They advised that I install a louvered (aka shuttered) dairy barn exhaust fan with a certain CFM capacity. I went up to the next size that more than doubled their recommended CFM.
It is a louvered 10" fan (1/30 hp motor) with circular guard behind it and louvers in front (outside).
I custom-built a pressure-treated wood crawlspace door for the fan. To allow rooms for the louvers, I mounted it on the inside of the door with two layers of p-t 2X4s and one layer of 2X4s (14" square).
For an electrical outlet to plug the fan into, you may be able to run off of an existing outlet circuit junction box under there.
My crawspace exhaust fan runs 24/7 during all but freezing weather (with the vents wide open). Been bone dry under there ever since.
Good luck!

Last edited by Mike Swearingen; 01-07-05 at 08:54 AM.
Old 01-08-05, 01:10 PM
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Well, I'm definitely out of my field here, but if the humidity is high because of the humidity naturally in the air, and not moisture coming from the ground, then what good does it do to blow in air that's as humid as the air you're blowing out. Mike's experience with the circulation drying it out seems to indicate that the moisture is indeed coming from the ground.

I still have to think that a ground vapor barrier will help a lot in slowing down the rate of moisture rising from the soil. In fact, there is a trend these days to "diapering" the crawl space by extending the ground vapor barrier all the way up to the rim joist.
Old 01-08-05, 04:08 PM
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Mike or anybody else,

Do you have any idea why a fan would cost approx $400?

Is this estimate of the "cost" a ripoff or truly what it costs
for an "all weather - waterproof" fan?

Just curious.

I will call the company you suggested when I get back in town
next week.

In the meantime, I was interested if any fan could actually cost
that much.

Thanks again for a great board (which means great posters)

Old 01-10-05, 10:55 AM
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Like John, this is not my field either. However, an experience I had in Poquoson, (SE) Virginia, near the Chesapeake Bay, would indicate that forcing air through the crawl space may or may not be the answer. It apparently does depend on the source of the moisture.

Long story short...my VA Tech extension agent, my termite/moisture control company, and a local contractor attempting to drum up business door-to-door said I had a moisture problem under my house. The contractor and the moisture control people wanted to install automatic vents and put sand under the house. The extension agent (making a profit was not his motive) said to install forced ventilation.

I followed the advice of the extension agent and installed a fan. Well, what had been a very damp crawl space became a lake. When I thought about it for a bit, I concluded that if I pull warm, moist air into my cool crawl space, I would probably be making the underside of my house into a giant dehumidifier. I took the fan out after trying it off and on for entire warm season. The experiment was repeatable.

Again, I am no expert, but I don't think the fan was the solution in my case.

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