Crawl space air vents are used to prevent the buildup of moisture in the foundation and subfloor of a house. The air vent allows outside air to circulate underneath the house, which keeps the area dry and stops mold growth.
An unventilated crawl space accumulates enough moisture to cause wood rot, mildew and mold, which can lead to structural damage. Air conditioners and heaters located in the crawl space can circulate contaminants, creating mold problems and distributing pollutants to other areas of the house. A moisture-rich crawl space also attracts unwanted pests, such as insects and rats.
In warm and humid climates, air vents in traditionally constructed crawl spaces are not able to prevent moisture buildup, so conditioned crawl spaces are used. Conditioned crawl spaces are sealed, insulated and use a vapor-retardant on the floor to control ground moisture. In a sealed crawl space, surface condensation, which occurs when the warm outside air meets the cooler inside temperatures, can be prevented. These crawl spaces also use a conditioned air supply or have mechanical exhaust vents installed, as opposed to the passive vents. Sealed crawl spaces also provide energy saving benefits by stopping the conditioned air supply from escaping.
Passive air vents can reduce energy efficiency in a home during winter months, due to cold air drafts. The heat-loss can be minimized by insulating the subfloor or the crawl space itself.