Crawl Space Vent Fan

**Matt Fellman** · 08-06-2009, 07:44 PM

I seem to remember that these circulating fans for crawl spaces have to be rated for continuous use and bathroom 'fart' fans don't work..... Here's one from today's inspection. Any comments?

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**Bob R** · 08-12-2009, 08:54 PM

I have seen 4" pancake fans used to ventilate damp crawls. Makes you wonder what these people use for brain.

Ron Bibler · 08-12-2009, 11:40 PM

I put this together sometime back. It ends up in 90% of my reports.

If anyone want a copy in msword you can send me an email.

ronofexcellence@earthlink.net

Best

Ron

A.D. Miller · 08-13-2009, 07:11 AM

Originally Posted by Ron Bibler

I put this together sometime back. It ends up in 90% of my reports.

If anyone want a copy in msword you can send me an email.

ronofexcellence@earthlink.net

Best

Ron

RB: Not bad for a biker . . .

**Brandon Whitmore** · 08-13-2009, 09:29 PM

Weird,

I posted on this yesterday, but it disappeared. I wouldn't doubt if that's someones idea of a complete vent system for a crawlspace. Matt, were there other vents installed?

Unless that thing is listed for continuous use, and for that purpose, I'd write it up. Did you document the model number by chance? It should have been on the fan somewhere.

**Matt Fellman** · 08-13-2009, 10:00 PM

Originally Posted by Brandon Whitmore

Weird,

I posted on this yesterday, but it disappeared. I wouldn't doubt if that's someones idea of a complete vent system for a crawlspace. Matt, were there other vents installed?

Unless that thing is listed for continuous use, and for that purpose, I'd write it up. Did you document the model number by chance? It should have been on the fan somewhere.

The strange thing was there was a vent opening between the front door and the garage and several across the back (townhouse) so had it not been there I wouldn't have made an issue of it. I usually only see these when there are only vents on one side.

I asked my contact at the county and he said the same thing - that there should be a rating on the fan somewhere (I didn't check - it didn't really sink in until I was out of the ridiculously small crawl space). He did say, though, that since it's on a humidistat that he'd let it slide since it wouldn't necissarily be running constantly. Not sure I agree with it but I pretty much left it alone. I talked to the buyer about it and showed him where it was and how to make sure it was still working.

**Bob R** · 08-16-2009, 05:04 AM

Ron
Thats a good diagram, too bad more builders haven't seen it.
I generally avoid giving repair advise as an Inspector. I feel some liability may come back to you if the recommendation you provide is followed, but just misses the mark (for what ever reason)to correct an issue. I feel it is better to let what ever person that is going to perform the repair do it in what ever manor they feel is correct, then, ALL responsibility for that repair is on them.

**Matthew Klein** · 08-16-2009, 06:44 AM

I would be hesitant to carte blanche recommend a ventilation fan for a crawlspace. The problem is that you could actually worsen the moisture in the crawlspace problem. For example, if the fan is pulling chilled air into the space, say at night, and then the day becomes warm and humid. You can create a situation where water literally literally rains from condensation surfaces. I have found this condition even in crawlspaces that weren't mechanically ventilated. I could not imagine what the situation would be like with outside air being pulled into one under those conditions. A control system, similar to (but not exactly the same as) an enthalpy economizer system should be installed to reduce condensation problems. Whether or not, if at all, to ventilate crawlspaces has been a debated issue for years. Some researchers advocate making the space as moisture and air tight as possible and extending the heating and cooling into the space, just as some advocate the same for attic spaces. From a biocontaminant standpoint, I am not so sure the crawlspace should be included in the home's environment that way. Who knows what is in the soil under a home.

**Ken Lyons** · 08-17-2009, 08:33 AM

Down in FL we have two ways of dealing with it. Either plenty of holes under the crawlspace so wind can easily pass through or seal it up tight and pressurize it from an AC duct. --No exhaust, no return.. just a supply to push clean (dry) air out. There is a bit of prep which includes plastic ground cloth and sealing the entire area.