Before uncapping a chimney, consider whether the cap slides inside or over the flue, and what type of fastening system is used to secure the flue. Caps that slide over the chimney and flue are most likely held into place with threaded fasteners, while caps that slide into the flue are typically secured with a caulk adhesive. Some types of chimney caps include slip-in, clamp-on and bolt-on, and all are constructed of either copper or aluminium materials.
Set up a sturdy ladder or scaffolding, depending on the height of the chimney; in some cases, the top of the chimney may be accessible from the top of the roof. Inspect the chimney cap to see if it is threaded on to the flue with fasteners, or if it is seated inside the flue and held into place with an adhesive or caulk seal.
Cut the caulk seal from the cap's lower base, where it meets the flue, using a sharp utility knife. Pull the caulk off by hand or use a sharp-edged scraper or chisel to remove any material that you can't easily remove.
Loosen any bolt fasteners that are located along the outer base of the cap using adjustable pliers or an open-end wrench. Remove masonry screws that may be present on some type of flue caps using a screw gun with either a Phillips- or hex-head bit.
Place your hands under the edge of the chimney cap and push up to dislodge it. Repeat the process on the other side, if necessary. Grasp the top of the cap once it is loose and pull it off of the chimney flue.
Slip a large slotted screwdriver between the cap and the flue if it doesn't come dislodged when it is pushed or pulled on. Pry the cap away from the flue using a slotted screwdriver. Push up on the cap again by hand until it dislodges from the chimney flue.
Wear medium to heavy duty work gloves when removing chimney caps, which may feature sharp edges. Use fall protection, such as a lanyard and harness, when working on a roof to prevent bodily injury.