It is a good idea to have your chimney professionally inspected before installing a chimney cap.

Chimney caps protect the chimney and flue from water and ice damage, enhance air flow and reduce the chances of unwanted animals and insects nesting within the chimney walls. A cap with a tight mesh spark arrestor can also reduce the risk of a roof fire.

Step 1: Measure your chimney. Outside mount caps are the easiest to install but require a minimum of 1 inch of flue protruding above the chimney crown. Cover all possibilities by measuring the outside and inside edges of the flue as well as the outside edges of the chimney crown. Also measure the height of the flue from the base of the chimney crown.

Step 2: Choose the chimney cap that best suits your needs. Once mounted, the top of the chimney cap should be at least 5 inches above the top of the flue. If the outside edges of the flue are rough, odd shaped or do not protrude more than 1 inch from the chimney top, you can purchase legs for the cap. The legs attach to the inside edge of the chimney cap and create tension to hold the cap in place.

Step 3: Once you have the correct chimney cap, read the manufacturer’s instructions before proceeding. Some caps come with an adhesive caulk. Use the caulk on the outside of the chimney only. The inside of the chimney will get too hot and cause the caulk to melt.

Step 4: Wear leather gloves to protect your hands from the sharp metal edges of the chimney cap. Set the cap in place and press it down, preferably 2 inches to 3 inches into or over the chimney flue.

Step 5: For outside-mount caps, tighten the mounting screws a little at a time to keep the cap squarely on the flue. If the cap does not have mounting screws, use a 3/16-inch Tapcon masonry drill bit to drill through the cap edge and into the brick. Hand tighten 1 1/2-inch to 1 3/4-inch long 1/4-inch Tapcon screws through the cap edge and into the brick. Mount the screws every 12 inches along the edge.

Once the cap is securely in place, you can rest better knowing that the bats and the wasps will need to find another place to call home.