And finally, affix your chimney cap to the chimney.
Some brands of top-mount chimney caps have sides that join with a
simple hinge-and pin, others have sides that assemble with an easy, tool-free locking system, and still other join with nuts and bolts.
Along the bottom of each of the four chimney cap sides are the flanges that actually attach to the top crown of your chimney.
You can use either adhesive or Tapcon screws (masonry anchors) and bits to attach the flanges to the chimney. Some chimney cap manufacturers provide you with
either the adhesive or the Tapcons when you buy your chimney cap. Or you can purchase them separately here.
To use the adhesive to install a top mount chimney cap, place the chimney cap where you
want it to be on your chimney crown (the concrete area surrounding the flue or flues) and bend the flange around the bottom of the chimney cap so that it conforms to the chimney crown.
Draw a line around the perimeter of the flange. Now, use your caulking gun to lay a 3/8 inch thick
bead of just inside the line. Leave 1/4 inch gaps in the adhesive bead at each corner of the
chimney cap. Move the caulking gun from side to side as you draw it along making a wavy line
about an inch wide from edge to edge, not a tight zig-zag. Press the flange of the chimney cap down into the bead of adhesive.
If you wish, you can use a putty knife to smooth the adhesive that oozes through the holes in the flange, but this is not necessary
To install a top mount chimney cap with Tapcon masonry anchors, you will need to buy a 3/16" masonry bit and enough
Tapcon screws to mount your chimney cap if the manufacturer has
not provided them with your chimney cap. Choose screws that are ¼"diameter and 1 ½" or 1 ¾" long. You will need enough screws to place one every running foot
around your chimney cap, but at least one on each side. For example, if your chimney cap is 17 by 24 inches, use one screw in the middle of each 17 inch side, a
screw at each end of each 24 inch side, and one in the middle of each 24 inch side.
To install, position the chimney cap where you want it to be on the chimney crown and conform
the flange to the chimney crown. Holding the chimney cap firmly in place, drill through the
predrilled holes in the flanges and into the chimney crown with the 3/16" masonry bit. As you drill
each hole, partially tighten a screw in it to hold the chimney cap in position. Then, finish tightening all the screws.
Some top mount chimney caps can be assembled with their flanges
facing inside of the screen box. If you have selected this mounting technique, simply remove the lid to screw in the Tapcons and then replace it.
If you don't yet have your chimney cap, take the FireplaceMall Chimney Cap EASY
MEASURE Guide up on the roof with you to help you correctly measure your flues and chimney for the type of chimney cap you need.
you
want it to be on your chimney crown (the concrete area surrounding the flue or flues) and bend the flange around the bottom of the chimney cap so that it conforms to the chimney crown. 
to mount your chimney cap if the manufacturer has
not provided them with your chimney cap. Choose screws that are ¼"diameter and 1 ½" or 1 ¾" long. You will need enough screws to place one every running foot
around your chimney cap, but at least one on each side. For example, if your chimney cap is 17 by 24 inches, use one screw in the middle of each 17 inch side, a
screw at each end of each 24 inch side, and one in the middle of each 24 inch side. 
