I live in Tigard, Oregon. Should I close off the crawl vents for the winter? I have for many years and feel it helps keep the floor warmer but now I have heard that it is better to keep them open to get rid of the moisture. I have black plastic laid over the dirt and have a sump pump that keeps the water from building up under the house.
KEEP THOSE VENTS OPEN!!!
Had your written from Minnesota, my answer might be a little different, but for folks who live west of the Cascades in places like Tigard or Seattle (wet but not too cold), the best advice is to keep as much air circulating through the crawl space all year round.
In Seattle we had a very cold snap (12F) a few years ago, and at that time I suggest