Measure the outer width and length of the chimney, using a measuring tape. If the brick chimney is fitted with a tile flue pipe, measure the outside of the flue pipe. You'll need these measurements when selecting the chimney cap.
Set the chimney cap in position over the brick chimney or flue pipe. If the clamping bolts on each side of the cap interfere, turn them counterclockwise by hand until the cap can slide in place.
Tighten the four clamping bolts by hand to hold the cap in position. Check the cap's orientation with a torpedo level. Make any necessary changes to ensure that the cap is set correctly.
Tighten each of the clamping bolts to the brick, using an adjustable wrench. When securing the bolts to a tile flue pipe, be sure not to over-tighten the bolts. Tile is brittle and is susceptible to cracking under excessive pressure.