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Old 05-21-2010, 08:22 PM   #1
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Cement crawl space ventilation


Hi -- new to the forum..

My 20'x30'x6' crawl space has cement floors, and stays very humid. Even with a large dehumidifier running the humidity is around 70%. The crawl area is where my furnace, hot water heater, and washer/dryer are located.

I ordered a 200 CFM powered crawl space vent which has a built-in thermostat and humidistat.. It will be installed on one side of the space and a standard non-powered vent on the other side.

My question for the forum is whether I should run a fan inside the crawl area to circulate the air, or just let the vent fan draw air from the standard vent?

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Old 05-21-2010, 09:48 PM   #2
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Cement crawl space ventilation


Depending where your located at. The power venting could make the crawlspace worse. Since it already has fresh air coming into it.

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Old 05-22-2010, 06:56 AM   #3
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Cement crawl space ventilation


sorry -- I'm in Georgia.

The humidistat will turn the fan & standard vents off if the humidity rises above a set level (like during a rain storm).

As of today there is no air coming into the crawlspace. No ventilation whatsoever.
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Old 05-22-2010, 07:02 AM   #4
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Cement crawl space ventilation


IS your water heater connected to a chimney? If it is, then air is being drawn into the crawl.

If it isn't, then the water heater is causing your humidity problem.
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Old 05-22-2010, 07:18 AM   #5
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Cement crawl space ventilation


It may be, but before the water heater was filled up & turned on I still measured 70% humidity. I'm currently at 70-75% with the water heater operational.
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Old 05-22-2010, 07:23 AM   #6
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Cement crawl space ventilation


A chimney drafts/draws air up through it, weather or not the water heater is filled or not, and weather the burner is on or not.
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Old 05-22-2010, 07:25 AM   #7
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Cement crawl space ventilation


I do not have a chimney -- there is a flue for the furnace, but that is closed off to crawlspace air as best I can tell.

I was planning to place the powered vent near the top of the wall, to pull the most humid air.
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Old 05-22-2010, 07:39 AM   #8
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Cement crawl space ventilation


Ok.

Where does the water heater vent to. Does it have a chimney. Or does it just vent into the crawlspace.

High humidity in a crawlspace, often comes from the crawlspace being vented.
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Old 05-22-2010, 07:48 AM   #9
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Cement crawl space ventilation


The house sat without power and water for several months. During this time, with no water in the heater (drained), and no ventilation, the humidity was around 80%. The previous owner had zero ventilation in this crawl space. I haven't added anything other than a dehumidifier (which feeds into a bucket I empty about once a day).
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Old 05-22-2010, 08:32 AM   #10
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Cement crawl space ventilation


Sorry.

Since you don't answer my questions.

I'll leave someone else help you. Good luck.

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