This adjustable width hood will work on openings from 28"w up to 48"w. The hood is required on most fireplaces with combustible mantels, and or trim work. Additionally, they serve to help the heat roll deeper into the airspace in your home. The ELH1 is designed to be mounted onto the lintel bar, or mortar joints with anchors and the provided clips. Each vent free product has it's own requirements set by the manufacturer regarding clearance to combustibles. Please follow those recommendations to avoid any unsafe conditions. **HOODS ARE TYPICALLY REQUIRED ON VENT FREE INSTALLATIONS INTO ANY KIND OF BOX THAT DOESN'T ALREADY HAVE AN INTEGRATED HOOD.**