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Texas Crawl Space vents open or closed in the summer?

Posted on 7/26/25 at 1:21 pm
Posted by STLhog
Dallas, TX
Member since Jan 2015
18758 posts
Posted on 7/26/25 at 1:21 pm
What do you guys say? Hearing and reading different things on the internets.
Posted by GoAwayImBaitn
On an island in the marsh
Member since Jul 2018
2807 posts
Posted on 7/26/25 at 1:49 pm to
Science tells me cool ground with warm air trapped above it makes for an air mass where the moisture will condense out of the air. I'd leave them open if you are in a humid region so that the potential "damp" air isn't trapped under house and it can vent out.
Posted by Hobie101
Member since May 2012
863 posts
Posted on 7/26/25 at 2:06 pm to
I need to vent my crawl space in summer to keep ductwork from sweating.

If your crawl space is conditioned (or cold because ac is escaping into crawlspace) and dry, I would leave shut.
Posted by prestigeworldwide
Member since May 2018
390 posts
Posted on 7/26/25 at 2:23 pm to
Following as we have the same issue here in Nashville. First home with a crawl space.

A/C company is coming out Tuesday to air balance the system because most of the rooms are 3.5 degrees hotter than by the thermostat.

The crawl space seems cooler than the house so I'll be putting a thermometer out there to check. Late afternoon the system can't keep up in the house and it jumps up 3 degrees and doesn't cool off until after we go to sleep.

I don't GAF about cooling the exterior/crawl space if it means my house gets hot. I just don't want to cause more issues if I have them close all the vents in the crawl space and then get mold or other issues.

I know the builder is going to piss on my leg and tell me it's raining but I'd to get information from an unbiased source

4 neighbors who used the same builder are all having the same issue. They gave us one unit for a 2 story house. No thermostat upstairs. Sorry for the rant but we're all curious as well.
Posted by Jmcc64
alabama
Member since Apr 2021
1702 posts
Posted on 7/26/25 at 5:00 pm to
get rid of them and ventilate crawlspace with conditioned air. 1 cfm for every 50 sq. ft.
why would you want hot humid air under your house condensing on every cool surface?
Posted by STLhog
Dallas, TX
Member since Jan 2015
18758 posts
Posted on 7/26/25 at 5:15 pm to
Does leaving them open not allow warm, humid outside air inside the crawl space to increase that condensation?

Pier and beam is such a nightmare in Dallas.
Posted by HBomb
Dallas
Member since May 2012
270 posts
Posted on 7/26/25 at 5:26 pm to
I’ve always left mine open in Dallas. Only time I ever close is if there is a winter storm
Posted by calcotron
Member since Nov 2007
10020 posts
Posted on 7/26/25 at 8:01 pm to
I leave the fan that blows air OUT of my crawl space on 24/7/365. It is encapsulated, albeit not that well. Ranges from 15 feet high in the back to 3 feet in the front. No moisture issues in 8 years.
Posted by Spankum
Miss-sippi
Member since Jan 2007
60167 posts
Posted on 7/27/25 at 10:30 am to
quote:

15 feet high in the back


Man, that is a hell of a crawl space!
Posted by Turnblad85
Member since Sep 2022
4168 posts
Posted on 7/27/25 at 11:38 am to
quote:

Pier and beam is such a nightmare in Dallas.




its a problem all over the south and getting to be more of a problem with increasing dewpoints.

Encapsulating is the best way to deal with it but not always an option given the terrain.

Sans encapsulation you want a good vapor barrier on the ground and plenty of airflow to carry the moisture that escapes the imperfect vapor barrier to be carried outside.

Dewpoints this wet summer have frequently been in the mid-70's. The coldest place in a home is the floor. When people keep their thermostats at 70*, the subfloor is near that temp--already about to start condensing water on the exterior side . Add in that under the house there is a lot of water-laden dirt/soil/ground, and the dewpoint under there can easily be 80* with a mediocre vapor barrier. Much higher with just bare ground.


OP, Vents [OPEN] CLOSED

Unfortunately if you bare ground and not even a vapor barrier, the little stupid 8x12" vents don't move enough airflow to help much.



Posted by calcotron
Member since Nov 2007
10020 posts
Posted on 7/27/25 at 12:08 pm to
quote:


Man, that is a hell of a crawl space


The people who built this house were morons, we should have a basement but now it would cost way too much for what we would get out of it. And it just has a stupid hatch to enter. I'll probably put in real double doors soon so we can actually store things under there.
Posted by Zappas Stache
Utility Muffin Research Kitchen
Member since Apr 2009
42200 posts
Posted on 7/27/25 at 1:16 pm to
quote:

Pier and beam is such a nightmare in Dallas.


I love my pier & beam and have been under there plenty of times running new electrical circuits, replacing old galvanized pipe, etc and never seen condensation. I've probably been under 10 or so pier & beams in Dallas helping friends with various things and never seen condensation. Keep them vented and your fine. Close up the vents and you're asking for trouble.
Posted by Turnblad85
Member since Sep 2022
4168 posts
Posted on 7/27/25 at 9:17 pm to
quote:

love my pier & beam and have been under there plenty of times running new electrical circuits, replacing old galvanized pipe, etc



crawlspaces are a godsend for reno work.

quote:

never seen condensation.


You'll pretty much never "see" it in water form as it gets absorbed into the wood as soon as the conditions are met. You will see it in the form of mildew or even failing or buckling plywood. The musty mildew air usually makes its way into the home and affects indoor air quality.
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