Does my crawl space need venting
Best practice varies with the climate.


If you open up venting between the basement and the dirt crawl, cover the dirt crawl with a moisture barrier.
Consider instead sealing the crawl entrance from the finished basement air, and opening a vent to the outdoors.
In SOME areas you may be allowed to put a fan to the outdoors. Mechanically controlled by humidity, it would offer the best of both cold and warm weather performance.


For research on this topic see, 

Moisture Solution Becomes Efficiency Bonanza in Southeastern United States, PDF by Bruce Davis and Cyrus Dastur, AdvancedEnergy.org -Crawl Spaces