Although air needs to circulate year-round through the attic, your home will likely be more comfortable if you cover the foundation vents in the winter. They have to be open in the summer, but to protect against the accumulation of moisture that may seriously damage your base.
In some parts of the nation, summer is the driest part of the year, and moisture abatement doesn’t become a prime issue prior to the winter rains begin. Homes in those parts of the nation benefit from open foundations at the summer since circulating air through the crawl space keeps them cooler. A draft at the crawl space also disappears moisture that may be left over in the wet season. That moisture may do more damage in the heat of summer than it may in the winter months.
Maintaining the base vents open during the summer is a no-brainer if you reside in a climate with warm, humid days and frequent summer storms. The vents provide crucial air flow that may not just prevent rot but also discourage termites and other pests. Humid air under the house threatens the base, and it may seep through the subfloor and tighten your hardwood flooring, even if the floor is protected by a moisture barrier.