Foundation Vents allow air to enter and exit the crawlspace. This airflow helps to remove heat and moisture. Fully closes at approximately 40, opens at 70. The crossflow of air helps protect against foundation problems. Heavy-duty construction, Premium bi-metal coil, Honeycomb grill, 16 in. x 8 in. rough opening, 50 sq. in. of net free area airflow each, Opens and closes automatically, Provides a functional way to vent the crawl space of the house. Easy to install, Fights damp rot, mold and mildew, Fights insect and pest infiltration.