If your crawlspace is unvented then it is being treated like an indoor space and may be adding too much moisture to your basement. This inexpensive device will tell you how much humidity it's causing. If the humidity is consistently high (over 40%) consider improving the moisture barrier and ventilation: see other posts with "crawlspace" tag. Of course it will also tell you if there is risk of frozen pipes also!
Click on image for link.
