Replaces old-style manual vents. Fits standard 8 in x 16 in vent openings. Automatically opens at 70 deg F 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 sq-in 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 in x 16 in.