HEARTLAND 21000 Energy Saving Dryer Vent Closure EASY-TO-INSTALL  Dryer vent closure with hassle-free installation. VENTILATION  Lets warm air escape when open. KEEPS COLD OUT  Prevents cold air from entering when closed and saves energy. NO PESTS  Prevents insects and pests from entering through dryer vent. VERTICAL INSTALLATION- Vent must be installed vertically and sliding may need to cut for proper installation.