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Repairing Your Damper or Cracked Flue

Please don’t yell at us, we know a flue is not a damper.

The terms, however, have grown to be interchangeable over the years, and we don’t want someone to miss out on good information just because they searched while using the wrong term.

To be clear, a flue is defined as any smooth walled channel that draws smoke or fumes out of a building. A damper is a device that opens up or closes off a flue.

People speak of “closing or opening the flue” and rarely speak of the device, the damper, that they use to achieve the feat.

Over many centuries of this, the two terms became one and the same to the general public.


Call it what you will, a damper is a piece of steel that seals off the flue through mechanical motion. They are used to control a fire’s intensity through manipulating the amount of airflow through the flue.


Fire Control

Damper function is rather simple. A metal plate covers the entry from the fire box to the flue. Manipulating the position of the plate controls how much, if any, air moves up into the flue.

Less airflow equals less oxygen and so a less intense fire. Increase the airflow and, you guessed it, flame intensity goes up as well. Cutting off all airflow will not, however, kill the fire.

The fire will run so long as there is enough oxygen in your home to keep it fed though, with the damper closed, the smoke has nowhere to go but into your home. Consequently, a closed damper is not a problem that goes unnoticed for long.

Home Protection

When your fireplace is not in use, closing the damper keeps air from flowing through the chimney. This prevents hot humid air coming in during the summer and cold air from blowing in during the depths of winter. Your damper also keeps debris out and small creatures from using your chimney as a doorway into your home.

Types of Failures

Some failures are easy to spot, some less so. There are certain things you will need to watch for both when you are using your fireplace and when it is idle.

Damper Not Opening

You want to keep a close eye on the flow of the smoke from your fire. Smoke should never flow into your room regardless of the fire’s size. Either you have forgotten to open the damper, or the mechanism is worn or popped free.

Damper Won’t Move

If you try to open or close the damper and it simply won’t pivot/swing/turn then either the damper mechanism is frozen or the damper itself is stuck in place.

Damper is Closed but Airflow Remains

Dampers can crack or simply get worn down by the ravages of time. Cracks and eaten away edges will allow air to continue to flow up the flue.

Rescuing the Old Damper

The mechanisms used to move dampers through their positions are designed with a large amount of tolerance. They can often be rescued with a thorough cleaning or replacement of a single element that you can fabricate on your own.

The damper plate, however, if cracked or worn, should be replaced rather than repaired. The metal fatigue, already evident in the damage you see, almost guarantees that repairs will fail or that more will soon be needed.

Repairing Your Damper

Repairing your damper is a straightforward process that can be a bit messy. You will need to access your firebox, so it is best to thoroughly clean out your fireplace. Lay out a tarp to keep the soot from traveling into your home.

Prepare the Space

Pull your door or screening and remove any grates to make accessing your damper a more comfortable experience. Scrub the area to make it a cleaner experience and prevent the possibility of losing a piece in all the soot.

Once you have the space down to the firebricks and a good tarp in place you can get to work. Well, more work.

Damper Types (throat)

Dampers come in three basic types of dampers used in masonry fireplaces as defined by their opening mechanism

  • Poker – banana shaped curve with teeth that catch on a bracket to position the damper via manipulation with a poker.
  • Rotary – has a knob accessible from outside the fireplace that is turned to adjust the damper
  • Double Pivot – uses two pivoting arms to lock the damper into position

Neither style is necessarily better than the other though the rotary’s access away from the flames is a nice touch.


You will note that it is very difficult to find information on throat mounted damper replacement. The industry has moved away from replacing throat dampers when they fail and moved to top mounted cap style dampers, which we will cover further down.

The best item we found to help those of us who prefer to stick to the original materials is this little guide from Vestal. It offers a good view of how throat dampers work and how they should come apart.

While each type is somewhat different the main points are the same. You must first disconnect the raising mechanism from the damper plate and holding bracket. Sometimes that means the removal of screws on others it is just cotter pins holding things together.

For the rotary style don’t forget the key/knob shaft coming through the wall.

Your damper plate will either rest its far edge in slots or rotate around a bar. Take the necessary actions to remove your plate once the raising mechanism is out of the way. Measure your plate and see if you can find a match or take it with you to a metalworker and have a replacement fabricated.

While you wait on your new damper, clean the throat opening and smoke shelf then take a look to make sure there are no other problems you should handle while you have access.

Once you have your new plate in hand and new (or newly cleaned) raising mechanisms prepared, put it all back in place in the reverse order from when they were removed.

Not This Time

This is where we would usually discuss how much it would cost to have a service come in and do the project for you. Well, the chances of finding a service willing to save your throat damper are slim at best so we have no pricing information to offer.

Modular fireboxes have taken over the fireplace industry and they come with their own dampers. Masonry dampers are a dying art and Vestal may be the only manufacturer left that supplies mechanism parts and damper plates.

New Industry Standards

The new standard is to simply remove the throat damper plate and mechanism and leave it out. They then go up top and install a top damper.

These dampers sit on top of your flue as it exits your chimney. A chain is dropped down and run through a bracket you install on the opposite wall from your dominant hand. This is for ease of use. Pull the chain taught and your damper is closed. Let it raise up and your damper is opened.

The only issues we have with these dampers is that you have to decide how much airflow you want before you strike the fire and the potential for freezing up between uses in the winter.

There is no adjusting airflow after the fire is going as the damper handle is deep inside the fire box. This video will give you a good idea of how this option works.


None of the manufacturers of chimney top dampers recommends DIY installation. The dangers of being on your roof are a constant, as we all know.

Professionals are able to mitigate the danger by using safety harnesses, lifts and other specialized equipment to protect them from falls.

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