If you check around the perimeter of floor above your crawlspace, you might be very very surprised to discover how much cold air is escaping through to your living space. This is especially common for those who have replaced carpeting, or gone from carpet to a hardwood or tile floor. To help reduce drafts, you can seal the molding running along the bottom of your walls with a silicone/latex caulk. This should reduce the air gaps leading from the crawlspace to the living space directly above. The actual crawlspace door is another big culprit for allowing cold drafts into the above living space. Many experts recommend insulating the door with a foam insulation board and then running weatherstripping around the perimeter of the opening to get a tight seal once the door is in place. If you have a hole drilled in the door to allow for its easy removal, try using a cabinet handle instead. You can then block off the old hole using the foam board mentioned above.
So the short answer to the question, should I block off my crawlspace vents during the winter, is no, if you want to be on the safe side. But using one or more of the above mentioned options will help reduce the amount of cold air introduced into your living space, thus improving both personal comfort level and energy efficiency substantially!
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