Grill Style 16 in. x 8 in. Mill Aluminum Foundation VentThe GAF Master Flow LW1 grill style foundation vent allows air circulation to reduce moisture and helps prevent decay in your foundation with a net free vent area of 50 sq. in. The vent is installed by nailing to floor joists or use as a block replacement. The LW1 is die cast aluminum with screen and a damper. The damper adjusts manually. Die cast aluminum Can be used as block replacement 50 sq. in. net free vent area Damper adjusted manually Screen