Following these 3 tips for installing a round chimney cap will help you prevent water damage to your building’s masonry and flue liner. The type of chimney cap required depends on the construction and arrangement of your chimney exhausts. Determine your needs and get measurements before selecting a cap. Plan your work down to the placement of the screws and make sure you have all the necessary materials.
1 - Select an Appropriate Cap
There are many different kinds of chimney caps. They can be made from copper, stainless steel, steel or aluminum, but stainless steel is the most durable material. The cap you install should include a spark arrestor or screen. This keeps animals, debris and rain out of the chimney while preventing sparks from reaching the roofing material. The standard mesh diameter is 3/4 inch, but the building codes in regions prone to wildfires often mandate a narrower diameter of 1/2 inch. Depending on the level of airflow in your chimney, you may select a draft-increasing vacuum cap or a cap with an integral damper. Be aware that designs with a turbine may get gummed up later by creosote deposits, while designs with a cross-sectional vent are not recommended for open flames.
2 - Select the Installation Method
The cap installation method depends on the type of chimney. Metal chimneys can be double-walled or triple-walled. An air-insulated metal chimney has a layer of air between the walls while a solid-pack chimney does not. If you are buying a round cap to fit one of these types, measure the inner diameter of the flue for the proper fit and measure the outer diameter of the chimney to size the secondary cap. This style of cap will often simply slide on or have to be tightened with pressure screws. If your chimney has multiple flues, measure the outside parameters. The chimney cap must be at least 5 inches above the tallest flue. With round clay tile flues, you can install some caps by just pushing them down into the flue and caulking the joint with a 3/8 inch bead of silicon sealant. If the flue ends below the crown of the masonry chimney, you may need a top-mounted cap with a leg kit or bracket.
3 - Plan and Install
Check the manufacturer’s specifications to see if the mounting bracket is applied with adhesives or screwed into the chimney with mortar anchors. If you screw the cap in, use 1/4 inch diameter screws that are 1 1/2 inches to 1 3/4 inches long. Place the cap flange on the crown to determine the height of the guide holes. Space the screws out at least 12 inches apart with at least one on each side of the crown. Drill with a 3/16 inch masonry bit. Tighten screws into the guide holes to support the chimney cap as you work around the perimeter.