Bolt the two steel hinges to the edges of the rectangular steel frame using two of the 4-inch steel bolts and the adjustable ratchet. Attach the hinges in the middle of the long edges of the steel frame.
Attach the rectangular steel plate to the hinges using two of the 4-inch steel bolts and the adjustable ratchet.
Use the electric drill to bore two holes in the sides of the chimney approximately 2 feet above the fireplace. Also bore two holes into each of the long edges of the steel frame directly below the hinges.
Attach the rectangular steel frame to the inside of the chimney by inserting the two 8-inch concrete screws through the bored holes in the edges of the steel frame and into the bored holes in the chimney.
Seal the rectangular steel frame in place by coating the edges of the frame with rubber cement.
Bolt each piece of the steel-linked chain to either edge of the rectangular steel plate. Pull each chain down to make sure the rectangular steel plate opens and closes properly.