How to Open Your Chimney Damper and How to Tell if it’s Open or Closed

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How to tell if fireplace flue is open or closed
top mount chimney damper controls diagram

A chimney damper prevents conditioned (warmed or cooled) house air from escaping through the flue when you’re not using the fireplace. You need to open the damper when you start a fire to allow for proper airflow and let the smoke out.

A closed damper can restrict airflow and become a safety issue since smoke would fill your house. Here’s how to tell if the damper is open or closed.

What Type of Damper Do You Have?

There are two main types of chimney dampers. Start by identifying what kind of damper is in your chimney if you’re wondering if it’s open or closed.

Throat Damper

chimney throat damper

Throat dampers are a common option because they’re convenient.  A throat damper closes the base of your chimney and insulates your home from cold air.  It’s easy to check if a throat damper is open or closed since it’s built into the fireplace and can be seen at the top of the firebox.

The throat, or upper portion, of the firebrick that lines the back of your fireplace should have a slight angle to guide smoke up and out while reducing cold air intake, and may slant towards the throat damper. This damper, located at the top of the firebox, swings down to seal the throat shut when you don’t use the fireplace.  Most dampers are constructed of cast iron or steel and will be black or rust-colored.

You can reach inside of the fireplace opening and behind the lintel to touch the damper. You should be able to open and close it with a knob  (this is usually located on the front face of the fireplace) or rod (located in the fireplace, above the firebox).

Top-Mount Damper
top mount chimney damper

A top-mount damper seals the chimney cap. This, in turn, insulates the entire chimney flue. The advantage of a top-mount damper over its throat-mounted cousin is that it prevents animals and debris from falling into the flue.

There is a spring that keeps the top-mount damper open, and the controlling cable or handle is usually attached to the fireplace wall. The open position is the default, and you will have to pull on a chain or cable and work against the spring to close the damper.

How to Know if the Damper is Open

How to tell if the damper is open or closed depends on the type of damper you have. Your house will quickly fill with smoke if you start a fire with a closed damper. You should get into the habit of checking whether the damper is open or not before starting a fire for safety reasons.

Here are different methods you can use to determine if the damper is open or closed.

Feel for a Draft

An open damper will let air circulate freely in the chimney flue. You should be able to feel cold air by moving your hand or face into the fireplace.

Note: This is not a foolproof method if you have a top-mount damper. Cold air stored in the chimney flue can give you the impression that the damper is open.

Visually Check

A visual check is one of the surest ways of checking whether the damper is open or not. Simply stick your head in the fireplace and look up.

If you have a throat damper, the closed damper immediately above your head will block your vision. You should be able to reach up and touch the closed damper.

If you have a top-mount damper, check for daylight at the top of the flue. If you can’t see daylight at the top, the damper is closed.

Check the Controls

The current position of the controls (cable, rod, handle, etc) can help you determine if the damper is open or closed as long as you’re familiar with the chimney and its controls. If you find yourself in an unfamiliar house, it’s best to perform a visual check after looking at the control position.

Do Not Start a Fire in the Fireplace if You Are Not Sure the Damper is Open

Some sources suggest you can check whether your damper is open or closed by simply starting a fire in your fireplace.  Starting a fire with a closed damper is extremely dangerous and should never be used as a testing method.

Having smoke fill your house is more than an unpleasant experience. You risk damage to the interior of your home, your belongings, and, most importantly, your health when a closed damper causes smoke to become trapped in the house.

If you ever start a fire without being sure that the damper is in the open position, keep an eye on the flames and smoke and open the damper as soon as you notice that airflow isn’t sufficient.

A closed throat damper will cause smoke to fill your house immediately when you start a fire. If you have a chimney with a closed top-mount damper It might take a few minutes for smoke to start filling the house, but you will eventually notice that there isn’t enough airflow.

How to Check the Controls and Open a Damper

It’s always a good idea to check the controls before starting a fire since a partially open damper wouldn’t allow for proper airflow even though you can feel a draft.

Different Types of Controls

Throat dampers typically have a rod that you push or lift to adjust the position of the damper (circled below):

chimney throat damper controls

Some chimneys have a knob that rotates a rod to adjust the damper.  These knobs are generally found on the exterior of the fireplace, usually centered above the fireplace opening, but sometimes off to the side.

Top-mount dampers use a spring-loaded design. They remain open until you pull a chain or handle, usually  mounted on the side of the firebox, to close them and secure the mechanism to keep the damper closed:

Chimney Fluefireplace flue open or closed

If the chain or handle isn’t firmly secured in the bracket, the damper is open.

How to Open a Damper

If you have a throat damper with a rod control inside the fireplace, check to see if you can push or lift the rod further.  A knob control on the fireplace exterior can be trickier since you might not know in which direction to turn it.

There is a simple solution:  Rotate it all the way in one direction and stick your head in the fireplace to check the damper position. It’s an easy way of figuring out which direction closes and opens the damper if the knob has no index markings.

If you have a top-mount damper, pull down on the chain to see if you can close the damper. The damper will immediately spring back up if you don’t secure the chain. This is also a good exercise to do before starting a fire to ensure that the top-mount damper is open all the way.

Telling whether a damper is open or closed will be easier as you become familiar with your chimney. You should be able to tell right away if there isn’t enough airflow once you get used to the chimney and what a draft coming from the flue usually feels like. Don’t forget to close the damper to preserve your home’s conditioned (heated or cooled) air when you’re not using the fireplace.

Questions About Your Chimney? Ask a Sweep

If you’re concerned that your chimney damper may not be working correctly or that any other part of your chimney is functioning improperly, the certified chimney sweeps and technicians at Priddy Chimney Solutions are ready to help.

Wonder if your chimney is in good shape? Contact us today to have one of our skilled chimney sweeps evaluate your chimney and fireplace.

How can we help?

Our team is available to answer any of your chimney, fireplace, or masonry-related questions.

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