How to Install a Chimney Cowl

a chimney on a rooftop
  • 2-3 hours
  • Intermediate
  • 100-600
What You'll Need
Chimney cowl
Mounting brackets or leg kit
Drill and masonry bits
Ladder and extension cord
Safety glasses
Tape measure
Spirit level

Once you know how to install a chimney cowl, you can prevent leaks and control drafts in your fireplace. Chimney cowls have metal covers and screens that serve as spark arresters and keep birds, rain, snow, and plant debris out of your flue. They may also have ventilators or dampers to modify the airflow in your fireplace.

Step 1 - Select Chimney Cowl

There are different types of chimney cowls suited to different types of chimneys. Stainless steel is the recommended material for resistance to corrosion from rain and creosote. If you are only going to cap a single flue, select a cowl that slides on. This type may at most require you to tighten some bolts to secure it. If you have a round tile or steel flue, select an inside mount cowl with brackets you will push down into the flue.

If you have multiple flues, you may need a cowl that connects to the outside of the chimney. Measure the outside perimeter of all the flues and the height of the tallest. The chimney cap’s screen must be placed at least 5 inches above the tallest flue opening. These types are fastened with an adhesive or masonry bits.

Step 2 - Access Roof

If you can reach the chimney from the rooftop, installing the cap should be fairly easy. If not, attempt to reach the chimney using a ladder from ground level. If the roof is sharply sloped or the chimney is very high, consider hiring a professional. Never set up a ladder with its feet at different heights. Have an assistant hold the ladder while you climb it.

Step 3 - Install Chimney Cowl

If you are using an inside mount cowl on a tile flue, caulk it into place with silicone sealant. If you are using an inside mount cowl on a metal flue, do not use the sealant. Metal chimney flues get too hot and can damage the sealant. For a cowl that attaches to the chimney, plan the spacing of the masonry anchors before attaching the cap.

Use at least one anchor on each side of the chimney. Keep the anchors at least one foot apart. Slide the chimney cowl flange onto the crown of the chimney and straighten it using the level. The manufacturer may have provided adhesive to hold the cowl on at this point.

Follow all provided directions for application. If the cowl must be screwed on, hold the cowl flange tight against the masonry and drill through both at once. Sink the masonry anchor, then insert the first screw into the bracket and tighten it into place. Drill the next hole on the same side as the first. Use the level and work around the perimeter of the chimney, tightening consecutive screws as you proceed.