In the summer, you close the vents to keep the warm moist air outside and away from the much cooler, drier air in the crawl space. However, if you have a water line near one of the crawl-pace vents, that vent should be permanently sealed and insulated to prevent freeze damage to the water line.How do you seal a crawl space?
If your crawl space is vented, you must close the vents when sealing from the outside. Cut a piece of the rigid foam insulation to fit the inside of the vent. Push it in place, then seal around the edges with expandable spray foam to create a tight seal.Does your crawl space need vents?
If, however, you cover the bare ground in your crawl space with an approved vapor barrier material, you only need 1 square foot of vent for every 1,500 square feet of space. The code also requires that there be one ventilated opening near each corner of the building. This is necessary to ensure a good cross-flow of air.