More on Crawlspace Ventilation....
I'm in IL and it gets quite humid here during the spring and summer. I'm new to the crawlspace ownership and last summer was my first with a crawlspace. I had the vents open all spring/summer and found that I had beads of water clinging to and dripping from all of the ventilation in my crawlspace. Naturally, this concerned me so I talked to a local heating/cooling expert who told me to keep the vents closed all year round and that the a/c would keep the crawlspace dry and keep the humidity out (as long as the vents were plugged up and closed). Is there any truth to this, or is he full of it? I need to know soon as we're approaching that time of year again and I want to keep my house in good shape. Thanks much! The last thing that you should do is close your crawlspace vents during humid seasons. The reason that they are there is to allow air to move ground and air humidity to prevent excessive moisture buildup under your house. This can cause wet insulation, rotted wood, dripping AC ducts and pipes, mold and mildew, etc. If what your heating/AC man said is true, why do they require cspace vents at all? And why would your ducts be leaking AC under your house, if they're properly installed and insulated? If your humidity there is causing your ducts/pipes to drip, then you should open all of your vents, and install an exhaust fan in your crawlspace door. I live in coastal NC where there is very high ground and air humidity. My ducts/pipes dripped for years, until I installed a 10 louvered exhaust fan with 580 cubic-feet-per-minute capacity. The cubic footage of my crawlspace (length X width X heighth)called for 250 cfm, according to W.W. Grainger technician that I consulted. Went with the next size up (580), and it keeps it dry as a bone under my house. It runs 24/7 on a little 1/30th hp motor (uses zilch power). My heating/AC people that installed my new system when I remodeled in '98 suggested getting an exhaust fan. I built a pressure-treated 1/2 plywood door, sandwiched 3 layers of p-t 2X4s (one out/2 inside) around the fan opening to hold it stable and give room for the louvers, and put an outside layer of screen and hardware cloth to keep out unwanted guests. The H/AC people have passed this design along to a lot of their other customers with the same problem, and it works like a charm. Good Luck! Edit: You can hook the fan up to a thermostat or humidistat, if you like, but I only turn mine off (unplug it) in the winter when I close up all vents to prevent water pipes from freezing. The fan housing louvers close off the fan opening automatically, of course, when the fan isn't running. Works for me. [This message has been edited by OldGuy (edited May 16, 2000).] The Old Guy said it all. Yes, you need a crawlspace exhaust fan. but, you need one big enough to cover your whole crawl space. Good Luck ------------------ Jack the Contractor Better listen to Jack and The Old Guy -- we just finished a $9500 repair job on an 8 year old house where the owner closed off his crawlspace ventilation for 2 winters in an effort to reduce his energy bills. Insulating the floor would have been a whole lot less expensive!! TommyBoy, another suggestion would be to install a Humidex, manufactured by Air Tech Equipment Ltd. of Shediac, New Brunswick, Canada (Toll Free 800-416-9111). It is really just a glorified circulation fan but very easily installed. I live right on the ocean in Nova SCotia and it has solved my wet crawl space problem. Of course, as everyone has recommended, we did have to maintain good ventilation during use. Good luck. Marilyn quote:Originally posted by TommyBoy: I'm in IL and it gets quite humid here during the spring and summer. I'm new to the crawlspace ownership and last summer was my first with a crawlspace. I had the vents open all spring/summer and found that I had beads of water clinging to and dripping from all of the ventilation in my crawlspace. Naturally, this concerned me so I talked to a local heating/cooling expert who told me to keep the vents closed all year round and that the a/c would keep the crawlspace dry and keep the humidity out (as long as the vents were plugged up and closed). Is there any truth to this, or is he full of it? I need to know soon as we're approaching that time of year again and I want to keep my house in good shape. Thanks much! The contractor put plastic down in our craw space. I was tolded to take the plastic up by one person and to leave it by another. I have just install a fan in the craw space, when I found damness and green moss on the ground under the plastic. The fan is doing good, but SHOULD IN REMOVE THE PLASTIC? John I stand by my first recommendation. Good Luck! Hey OLDGUY, JOHN HERE! DO I TAKE UP THE PLASTIC THAT IS ON THE GROUND UNDER THE HOUSE? I HAVE BEEN TOLD YES AND NO. Leave the plastic down. It's keeping any ground moisture from coming up into the crawl space. More than a Carpenter http://www.carpenter.cjb.net I've been doing research but I want to make sure I'm on the right track. I'm trying to close a house and the crawl space is an issue. This is what the seller originally wrote: Contractor inspected crawlspace. While there was no standing water in the crawl space, the area did seem damp due to a lack of air flow. Contractor recommended installing a fan to increase the ventilation. Seller will install a fan in the crawlspace. No additional repair required. When I did the walk-through, a box fan had been placed on the ground and plugged into an outlet on the light socket. I was expecting something like the crawl space ventilation fan. I let go of some more fixes relating to the crawl space b/c she said that she would install a fan and so we are now holding up the closing until this has been addressed (either fixing it or lowering the price of the house so I can fix it). Am I right in thinking that an unsupported box fan is not an acceptable fix? Welcome to the forums! There are two schools of thought on this, and you will get both sides, so the choice will still be yours. Not sure where you live, so some information may change once you fill out your profile and let us know. Here in the South, we are required to install crawlspace vents opposing each other on all sides. This creates a cross ventilation of the space and keeps moisture to a minimum, since fresh air flow evacuates the moisture that has gathered there. The other side of the argument wants you to seal up the space, insulate it, run air conditioned air down there, and other things, but I'll let them post their advice separately. Really depends if your in a tri-level or not. If the crawlspace is open to teh rest of the basement, then yes close off the vents. Leaving them open is like leaving a window open with the a/c on. If your crawl space is closed off from the rest of the conditioned house, then yes leave them open in the summer and close them off in teh winter. Crawl space in green grass areas should not be vented. With vents open you let in the humid air. exhaust fans and the humidex that was talked about will not help they will pull more RH in. VB needs to stay on the ground with seams sealed and up the walls to ground level.
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