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Chimney Damper: Everything You Need to Know

May 24th, 2024 | 4 min. read

By Louis Greubel

A Draft King Universal Chimney Cap with a chimney damper installed on a mock masonry flue against a white background.

A chimney cap is essential to any masonry flue. It keeps the rain and snow out, it helps to prevent certain downdrafts, and it keeps wildlife like raccoons or birds from making a home in your chimney. If you have a chimney on your home, that chimney should definitely have a cap on it.

As great as they are, though, chimney caps can only do so much to offer protection. For the cap to allow a good draft, the mesh needs to be relatively wide. Even the smallest mesh possible on a chimney cap will still let in stink bugs, cicadas, bees, wasps, hornets, and more insects.

Also, there’s the matter of temperature. When it gets cold out, a wide-open flue will allow frigid air to get in. That alone can lower the temperature in your home by several degrees.

For those looking for the maximum possible protection on their chimney, adding a chimney damper is the best thing to do.

But what is a chimney damper, anyway? How do they work? What sizes do they come in, and how do you go about installing one?

In this guide, we’re going to dive into those questions and plenty more. By the time you’re finished here, you’ll know everything you need to know about chimney dampers. And, most importantly, you’ll know whether or not you should add one to your masonry flue.

What is a Chimney Damper?

A chimney damper with its steel cable and ball chain lying on a black carpet shot from the top-down.

A chimney damper consists of a spring-loaded metal plate attached to an anchor system. The metal plate is attached to a long, spring-loaded stainless steel cable. That cable runs the length of your flue, terminating in your firebox.

A GIF of a Draft King chimney damper closing over a fiberglass gasket and flue tile.

To close the damper, all you have to do is pull on the handle at the end of the stainless steel cable. The damper comes with a bracket that anchors into the masonry in your firebox. After closing the damper, just slide the handle into a slot in that bracket. This will keep the damper closed.

A chimney damper firebox bracket and ball chain handle lying on the surface of a wooden table.

Chimney Damper Safety Tip

Be sure that you never leave the damper closed when burning wood in your wood burning appliance. If the damper is closed, smoke, carbon monoxide, and other combustion byproducts will have no way to escape your flue. Instead, they’ll end up rolling back into your home.

To seal bugs, wildlife, and insects out of your chimney, you should keep the damper closed when your heating appliance is not in use. But always double-check that the damper is open before starting a fire in your firebox.

Chimney Damper Sizes

A thirteen-inch by twenty-inch and a thirteen-inch by thirteen-inch Draft King damper kit thumbnail against a white background.

At HY-C, we manufacture chimney dampers in two different sizes under our Draft King brand name. They’re designed to be used in conjunction with our universal chimney caps, which themselves are designed to work on just about any chimney flue size you’re likely to come across.

We make a damper for square flues and a damper for rectangular flues. Each damper shape is designed to fit a range of flue tile sizes:

  • The Draft King square damper fits flues between 8” x 8” and 13” x 13”
  • The Draft King rectangular damper fits flues between 8” x 15” and 13” x 20”

As long as your flue tile falls somewhere in this size range, our Draft King dampers will work for you. These sizes encompass approximately 90% of chimney flues around. Be sure to measure your flue before making a purchase, though, to ensure a Draft King damper will fit your flue.

How to Install a Chimney Damper

A Draft King chimney cap with a chimney damper installed on it. The cap is without its hood.

After you’ve found the correctly sized damper for your flue, the next thing to do is install it. For those who aren’t as DIY-inclined, a chimney sweep or professional roofer can do the job for you.

But, if you’re interested in installing your damper on your own, we’ll detail the process below. We’ll also provide more in-depth instructions with images in PDF form. Just click the button below to access them.

Chimney Damper Installation Instructions

Tools Needed

  1. An adjustable wrench
  2. Diagonal cable cutting pliers
  3. Industrial scissors
  4. Standard caulking gun
  5. An electric drill
  6. A ½” masonry drill bit

Chimney Damper Installation

Note: these instructions assume you’re using a Draft King Universal Chimney Cap and Damper Kit.

To begin, let’s take an inventory of the pieces provided:

  1. Spring-loaded damper plate and anchor system with steel cable attached
  2. Ball-chain handle
  3. Fiberglass flue gasket
  4. Firebox bracket
  5. Masonry screws (2)
  6. Chimney cap cage with crossbar
  7. Chimney cap hood
  8. Wing nuts (2)

Start by centering the cage of the chimney cap on your flue tile. Place the fiberglass gasket inside the cage along the top of the flue tile. Once the gasket is lined up properly, trim it down to the correct size.

Now, take off the cage and the gasket. With your caulking gun, lay a heavy bead of silicone on the top of the flue. Set the cap cage on top, and lay another bead of silicone around the cage (where the flue and the cage meet).

A close-up of the gasket of a Draft King chimney damper installed with silicone beading over the cage of a Draft King Universal Chimney Cap.

Press the gasket onto the silicone to ensure it sticks to the cage and the flue. The gasket will create a seal for the damper when it’s in use.

Finally, thread the 32’ stainless steel cable attached to the damper through the center hole of the crossbar, allowing the cable to slide down your chimney flue. Set the damper assembly over the two studs of the chimney cap cage, place the chimney cap lid over the same two studs, and attach everything together with the two wing nuts provided. The completed cap installation should look like this:

A Draft King Universal Chimney Cap with a chimney damper installed on it. The damper is in the open position.

Now, head down to your firebox and locate the other end of the stainless steel cable. Using your ½” masonry bit and two masonry screws, install your firebox bracket about two feet above the floor of your firebox. Drill the bracket in place with the screws, and tighten them with your wrench.

Next, thread the ball-chain handle through the keyhole slot in the firebox bracket. Let it hang. Locate the 32’ steel cable and slide it through the lock on the ball-chain handle, making a double loop.

A chimney damper steel cable attached to the damper's ball chain handle which itself is attached to the firebox bracket, all lying on a wooden table.

If the steel cable is too long, disconnect it, trim it a bit, and attach it again. Repeat this process until the steel damper cable and ball chain work correctly in conjunction with the firebox bracket to allow the damper to open and close properly.

At this point, the damper installation is complete! When you want to close the damper, just pull the ball chain handle down and allow it to lock into place on the firebox bracket to keep the damper shut.

Should You Get a Chimney Damper?

And there you have it: a crash course on chimney dampers. We covered what they are, how they work, what sizes they come in, and even how to install them.

The question is, though, should you install one on your chimney?

Dampers certainly have their benefits. They seal out even small insects and keep the cold out of your home during the winter months.

To decide whether or not one fits for you, though, the first thing you should do is measure your chimney flue. If a damper wouldn’t fit, obviously it wouldn’t be worth your time.

If your flue is the right size, the next thing to consider is installation. If you feel like you’re handy enough for a DIY install, give it a go. If you don’t trust your skills, though, you’ll have to pay a professional to install your damper, so keep that time and cost in mind.

For additional hearth accessories and add-ons, check out Liberty Foundry Co. From smoke guards and firebacks to fireplace grates and stove boards, you’ll find plenty of cost-effective solutions to help you enhance your hearth.

Louis Greubel

Louis earned a bachelor's degree in English with a focus in rhetoric and composition from St. Louis University in 2017. He has worked in marketing as a content writer for over 5 years. Currently, he oversees the HY-C Learning Center, helping HY-C subject matter experts to share their decades of home solution products experience with homeowners and sales partners across the country.