Replaces old-style manual vents. Fits standard 8" x 16" vent openings. Automatically opens at 70 degrees Fahrenheit and closes at 40 (approximately). The key mechanism, bi-metal coil, fully enclosed in protective cover. Stainless steel compression spring with 1 adjustable screw for easy installation. 65 square inch net free area. High-density thermo-plastic construction. Stainless steel and corrosion resistant metal parts. Heavy-duty aluminum mesh screen, front and back. No electrical hook-up required. 8" x 16".