Everything You Need to Know About a Fireplace Damper

What Is a Fireplace Damper?

A fireplace damper is a small door inside a fireplace, usually near the base of the chimney. Typically made from cast iron or other heat-resistant metal (sometimes ceramic), the damper essentially opens and closes the chimney. When someone refers to “opening the flue” of the fireplace, what they really mean is opening the damper.

When a fire is lit, an open damper lets the smoke, soot and gases escape out the chimney. When the damper is closed, it prevents cold air from entering through the chimney.

Because a properly functioning open chimney has an updraft — the negative pressure that pulls smoke up and out — it can also pull out heated and air-conditioned air unless you have a damper. But remember that a closed damper and a lit fire is a recipe for disaster, as smoke and toxic fumes will quickly billow out the front of the fireplace to dirty and stink up the house.

Does My Chimney Have a Fireplace Damper?

Your fireplace probably has a damper. Because of their importance for safety reasons, most local building codes require one. If you’ve purchased an older home or a home where the owner built a DIY fireplace without building permits or inspections, then it’s possible you don’t have a damper.

Whether your fireplace is gas or wood-burning, if it was built with a pre-fabricated insert, then it almost certainly has a damper. And while older wood-burning fireplaces can function safely without a damper (gas fireplaces cannot), a chimney without a damper is just a gaping hole in the roof of your house. It’s a gateway for frigid air to enter and for heated air to escape in the winter.

In the summer, the updraft can rob air-conditioned air from your home, or a low-pressure system can push hot air in. And if there’s no screen or other protection at the top of your chimney, it’s also a chute for insects, birds and rodents to enter your house.

Types of Fireplace Dampers

Traditional wood or gas fireplaces have one of two types of dampers.

• Throat dampers are installed at the base of the chimney, over the firebox — the main chamber where the fire burns. They’re usually opened by a handle, a crank or a chain located inside the fireplace.
• Chimney cap or top-sealing dampers are installed at the top of the chimney. They are opened with a chain located inside the fireplace.

How to Be Sure the Fireplace Damper is Open

Always confirm the damper is open before lighting a fire. If you’re not sure which is the open or closed position on your damper hardware, try one or more of the following steps:

• Look inside the chimney with a flashlight. If you have a throat damper, you’ll see it in the open position.
• Check for a draft. Place your hand in the (unlit) firebox. If you feel air moving, the damper is open.
• Test with fire. Light a piece of paper on fire and hold it under the chimney. If the flame and smoke are drawn upwards towards the chimney, the damper is open.
• Look outside. If you have a chimney cap damper and you’re still not sure it’s open, go outside and check. Bring binoculars if necessary.

Installing or Replacing a Fireplace Damper

Over time, a damper can warp or crack due to intense heat, and it will need to be replaced.

A throat damper is a simple mechanism that is most often held in place by a metal rod that’s attached to the chimney with four nuts. Loosen these — they may be rusty — and wiggle the old damper off the rod and out of the chimney. Take the old damper to your local home improvement or fireplace supply store and buy one the same size. It should attach to the existing rod, which you can retighten with the same nuts.

Unless you are comfortable climbing up on your roof with a safety harness, installation or replacement of a chimney cap damper is best left to professionals.

A properly installed damper should provide decades of worry-free use, especially if you have a screened chimney cap to keep water, debris and animals from entering your chimney.

Fireplace Damper Cost and Installation

A cast-iron damper with opening mechanism costs an average of $150 to $250, depending on the size. If you only need to replace the damper plate, these cost around $50. A chimney cap damper costs around $200 to $300, not including the screened chimney cap, which runs between $90 and $120. Professional installation of a new damper will likely run around $200 to $400 for labor, in addition to the cost of the new damper itself.