How to Install a Premade Fireplace Box

Measure the inside of your fireplace and the inside of the chimney. Ensure that your premade firebox will fit into the fireplace with little adjustment. You should have enough room between the surrounding fireplace and the firebox that you can tighten the flue liner to the flue opening on your firebox.

Slide the premade firebox into the fireplace and push it back as far as it will go. The back of the firebox should touch the back of the fireplace's wall.

Climb up onto the roof and lower the flue liner down into the chimney until it reaches the top of the premade firebox. The flue liner size will be indicated by your firebox on the flue opening and in the firebox's manual. In some cases, the flue liner will come with the premade firebox.

Slip the flue collar over the top of the flue liner and the chimney. Tighten the flue collar into the sides of the chimney with screws using the screwdriver. If you don't have holes in your chimney for the screws, drill new holes using a drill bit one size smaller than the screws you are using.

Climb off your roof go inside of your home to your fireplace. Grab the flue liner you lowered down the chimney and fit it over the flue opening on your premade firebox.

Slip screws into the flue liner and flue opening and tighten them with the screwdriver. Apply fireplace caulk around the flue liner where it meets the flue opening in the firebox. Dab fireplace caulk into the screw holes as well.

Fit the firebox's side panels between the firebox and the chimney. Use the drill and screws to attach the panels to the side of the fireplace and the firebox. Place the top panel over the firebox and drill it to the top of the fireplace and the firebox.

Squeeze a thick line of caulk around every gap between the firebox and the fireplace or the firebox and the panels.