Dear James: During winter, I feel a breeze coming down the fireplace chimney even with the hearth damper closed. Also, I think raccoons and bats get down in there. Will installing a chimney-top damper help? -- Karl T.
Dear Karl: A fireplace certainly is a pleasant and attractive feature for a home, but it allows many unwanted "things" to enter your home down through the chimney. Cold air and a occasional bat are not uncommon. Raccoons are generally too large to enter your home, but they can drop fleas which end up in the carpeting near the fireplace.
Most fireplaces have a damper in the throat of the chimney just above the firebox. This is designed to keep pests and air leakage out of your home when a fire is not burning and the damper is closed. If installed properly, it can be quite effective when new.
The problem is after it gets old, it no longer seal well. This can be caused by creosote or other deposits where the damper seats in its frame. Also, when one is very old, it can rust through leaving gaps large enough for a bat to squeeze through or fleas to drop through.
It is possible to replace a chimney throat damper, but installing a flue-top damper makes more sense and is a relatively easy do-it-yourself project. A good quality flue-top damper costs between $150 and $300 depending upon the size of the flue opening at the top of the chimney.
There are two basic damper designs. One is a pop-up design and the other is a hinged design. When they are closed, they seal well and definitely keep any animals from entering the chimney. If you have many snowy days, the pop-up style may be better because when it opens, it will not allow snow to slide into the chimney top as may happen with the hinged design.
Both designs include a stainless steel cable, which runs down the chimney into the firebox. This cable is used to open and close the damper. The cable should last many years and can easily be replaced when it wears out. Stainless steel cable is available at hardware stores or boating supply outlets. If the cable breaks, the damper automatically moves to the open position.
Damper kits come with a metal frame which is mounted over the top of the chimney flue. They are spring-loaded, so they open when your release the tension on the stainless steel cable. The pop-up design has diagonal springs which keep it level as it opens.
Most of the flue-top damper manufacturers recommend just gluing the metal damper frame to the top of the flue with high-temperature silicone sealant. This should be adequate to hold it in place, but if you prefer to screw it to the flue with brackets, use stainless steel brackets and screws.
When working with flue tile, keep in mind it is very brittle. Use a tiny masonry drill to make a pilot hole for the bracket screws. Follow this with a 1/4-inch drill bit to finish the holes. Don't over-tighten the screws holding the brackets to the flue.
Apply ample silicone sealant and press the damper frame down into the sealant eliminating all voids. Attach the damper housing to the brackets to secure the damper assembly in place.
Send your questions to Here's How, 6906 Royalgreen Dr., Cincinnati, OH 45244 or visit www.dulley.com.