The UnderAire Series crawl space ventilators from this company circulate fresh outdoor air underneath homes and porches. According to the company, excessive humidity levels in crawl spaces is the leading cause of premature rotting of support columns, joists, floors and beam supports. Humidity can promote fungus growth, increase termite activity and cause plumbing failures due to rust and corrosion. All models of the ventilation fans include a factory-installed and pre-wired thermostat. Deluxe models include a de-humidistat.

Tjernlund Products Inc., 1601 Ninth St., White Bear Lake, MN 55110; (800) 255-4208; fax (651) 426-9547;