How to Cap a Chimney

A chimney cap keeps rodents and birds from getting inside your chimney and wreaking havoc. A cap also keeps rain out of the chimney, which is important since moisture and water could compromise the inner workings and the structure of your chimney over time. There are two basic types of caps: those that go on top of the chimney and those that go on the inside. Capping a chimney is a fairly easy job and should take a half an hour at the most.

Things You'll Need

  • Chimney cap
  • Protective gloves
  • Tapcon masonry anchors
  • 3/16" masonry bit
  • 12 masonry screws, 1-1/2" or 1-3/4" long and 1/4” in diameter
  • Putty knife
  • Silicone sealer
  • Caulking gun

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Outside mount chimney cap

Place the cap over the crown of the chimney. The crown of the chimney is top portion of the structure that tops it off.

Cover the top of the flue with the chimney cap. The flue is the pipe that runs down into the chimney.

Use the fasteners or screws that came with the cap. Tightly screw in all of them.

Find Tapcon masonry anchors, a 3/16-inch masonry bit and about a dozen masonry screws that are 1-1/2 or 1-3/4 inches long and 1/4 of an inch in diameter.

Put the chimney cap on the chimney crown. Bend the flange onto the crown. Drill holes through the flange and into the crown. Put a screw in each hole after you drill it so the cap does not move. Tighten all of the screws when all of the holes are drilled and screws are in place.

Inside mount chimney cap

Place the cap inside the flue.

Push the cap down into the flue. It should be a snug fit, with the edges of the cap rubbing against the inside of the chimney.

Bend the edge, known as the flange, of the cap so it fits to the crown of the chimney. Draw a line around the perimeter of the flange.

Using a caulking gun and apply a 1/2-inch wavy line of silicone sealer inside the line. Press the flange down and remove the excess sealant with a putty knife.

Tips & Warnings

  • If your flue is metal, do not use sealer since it will not last with the heat from the chimney.


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