Fireplace Damper Problems

This is my conversation regarding a damper problem that one of our Ask the Chimney Sweep readers had.

Top Sealing Damper
Lock-Top II incorporates rain cap, bird-screen and spark arrester all-in-one. Plus it saves energy.

Question from Reader

But, how does this work when I’m in a condo and the top of the fireplace has a raised protective cover that covers 2 holes (one from my condo’s chimney and one from the condo above me)?

A.) I would want to discover why that damper is stuck. Is it because it is out of round, warped metal or just rusted closed?
Then I would be checking to see if there is a replacement damper blade available from the manufacturer. Most competent chimney sweep contractors can install this for you!

This is the Lock-Top II top-sealing damper in a closed position saving you lots of energy dollars.

To start your hunt, grab a flashlight and begin to look for a riveted, small metal tag to the fireplace metal framing. It is hiding there somewhere; this tag will provide you with the needed information of who the manufacturer is, the model number and serial number.

Then go online and start gathering your information.

While pour hunting for this damper replacement, look for that manufacturer’s UL  “glass-doors”, if they manufacture them.
My experience is that many prefab glass doors will work as well as a damper, in controlling air movement of the fireplace. May I caution you put just any set of doors on your fireplace, as many glass doors are not tested for your unit and may end up blocking air vent that is required to cool the fireplace off.
I caution you on installing any type of top sealing damper on your condo chimney top, as it most likely is not UL listed for your fireplace. Also, let’s not forget that you have that unique situation where I believe someone has installed “sides” on the top, not designed or provided by the manufacturer. In the past, I have dealt with draft and smoking problems with some aftermarket installs (shroud metal side covers) that were not designed and UL tested for that fireplace manufacturer.
These are my own insights.


Readers reply:

Your answer confusing me but I realize that maybe you are talking about a prefab fireplace. My condo building (over 30 years old) is brick, the fireplace both inside and outside is also brick and when I had someone clean it they said it was a masonry fireplace, So, does this change your answer?

(Clay’s reply to Reader) and more fireplace damper

Millions and millions of these types of throat dampers were installed in the 60s, 70s, and 80s.

I apologize and yes I’m jumping to conclusions thinking that you were referencing a prefabricated fireplace. Please allow me to re-edit my reply. Discover why that damper is sticking. Is it a warping metal blade or just rusting closed? Then I would be checking to see if there is a replacement damper blade available from the manufacturer.

To start your hunt, grab a camera, flashlight, and tape-measure, and get into the firebox (after it cools and the wood ashes dissipate, that is, assuming that is wood burning in hopes of discovering the manufacturer or your damper. Often the manufacturer’s name is on the damper frame (i.e. Vestal, Majestic or Donnelly).

It is my experience that, all of these manufacturers’ are very popular and are still available at your local brickyard. On a personal note I have purchased many dampers and just used the valve blade and handle and threw the frame away.

If this were mine have a top-sealing damper. If this was my property, using a *Lock-Top II damper.

Lock-Top II

I personally use this damper because it offers a rain cap, spark arrestor, animal screen and damper all in one. Another benefit of using a top-sealing damper as it actually has a payback (ROI), saving you energy dollars.

Installing a top sealing damper actually allows for the preheating of the entire chimney flue stem with warm house air, often making it much easier to start a (wood) burning fire, while at the same time sealing the cold air out, while your fireplace is not in use.

Remember, it also prevents hot air moving through the chimney during the summer–time AC usage.

Regarding your statement “the top of the fireplace has a raised protective cover that covers 2 holes (one from my condo’s chimney and one from the condo above me)?” I recommend speaking to your chimney contractor about that issue.

Burn safe and warm while saving some energy!


AsktheChimneySweep YouTube

For more information on top-sealing dampers, check our YouTube video from our Ask the Chimney Sweep channel!

Make sure that if you buy these dampers, you make sure it is the right size!

Clay Lamb
Latest posts by Clay Lamb (see all)

4 thoughts on “Fireplace Damper Problems

  1. I have a 4 floor apartment with fireplaces on all floors. Each fireplace has a separate chimney duct but all 4 run side by side and end together on the roof.. There is one large metal weather cover on top for all four fireplaces. Sometimes the smoke goes from one floor to another when only one fireplace is working. Since there all together at the top I was hoping that if I put a divider between each top opening to separate them up until the top of the hod cover it will prevent the downdraft from one to the other.

    Appreciate the help

  2. Greetings, Steve.

    We’re going to refer to this as thermosiphoning. This is where the air is moving up the chimney and due to other negative pressures in the building it is moving back the down the flues, (I will refer to this as chimney flues instead of ducts so we’re on the same page).

    Often these issues are due to air and balance issues and can be resolved by one of many ways; there is not the single answer! It could be raising flues to random heights by 6″ to 8″ inches and putting individual caps on or it could be doing what you suggested (which I think is a good idea) of putting dividers in there. This is where I would start.

    MOre info: Negative pressures in the house or air and balance could be caused by large catheral ceilings, very large stairwells, powerful fans in kitchens and baths, I have even seen it where the speed on the furnance blower is set high to move the heavier cold air and it definitely can affect the air movement within the house being pulled into the cold air returns. I hope this little brainstorming with you helps! Wish you the best in tackling this issue. Its often trial and error!

    Regards Clay

  3. Clay,
    I just happened onto your site as I was looking for some other content. Great site, and I’ll be hanging out here more as I have a cabin in the UP that I’ll be outfitting with a wood stove!

    My Dad has a similar thermosiphoning issue as Steve does… He has two fireplaces, one in the basement and one on the main floor directly above it. They share a common chimney chase (which is a “bump-out” to the house structure) with two flues side-by-side. They also terminate at the same elevation above the roof as was indicated above. I don’t know for certain, but suspect that the chase is a cold air chase (un-insulated). The downstairs appliance is a gas log unit, with a 24/7/365 pilot light and a damper which is restricted from closing fully to allow pilot combustion exhaust. The main floor fireplace is a “gas assisted” wood burning fireplace with glass doors. (The gas burner makes starting the wood easy, but is not typically used as a gas-only appliance). (House was built in the early-1990’s – near Madison, WI).

    When he uses the main floor fireplace (burning wood) he gets smoke in thru the basement damper. More-so in the last few years because they replaced the windows with better ones creating a tighter house. The only way he has been able to combat this at all is to run both units at the same time… but I don’t think it is 100% effective.

    He had a “fireplace guy” come out and look at it; and then install a baffle (piece of sheet steel) between the two flues… similar to what was mentioned in the issue and response above to Steve; but that didn’t help. I had doubted that it would since I guessed that there was enough draft to draw air around the baffle – especially with the basement flue “propped open” for the pilot light.

    He has had another guy come out and look at it (since he couldn’t get the first guy to come back after taking over $400 for his “fix”). They were looking into extending the main floor flue by 2-3 feet to gain separation; but this guy never followed-thru. Something about not being able to find compatible chimney pipe to do so. This “extension” is also something similar to your recommendation to Steve (6-8″ random flue heights).

    While I like this latter approach… from what I’ve read in my searches, it is against code to have any seams above the
    “chase”/flue support. How would you go about this while staying within code? The “chase” is vinyl-sided most of the way up, not brick faced.
    I’ve wondered if Dad would see improvements if he were able to convert the gas-log basement unit to a pilot-less ignition system (retrofit to the current unit) and remove the damper restrictor, thus allowing the damper to fully close. Or, just shutting off the pilot light in the basement and closing the damper fully. He doesn’t use the basement unit much; so he is really just wasting NG with the pilot light anyway, while also creating a vent path for the house when the main floor fireplace is drawing and needing make-up air. But, I’m afraid that the house might be tight enough now that this could still be a “lowest restriction pathway” for make-up air; not sure how to confirm that thought other than thru trial and error.

    Dad’s in his 80’s, so he questions the ROI (to him) on spending the money to replace either/both units with new high-efficiency units as the second guy had mentioned would be a certain fix…

    He’d like to use the main floor fireplace more often, but doesn’t want to open a window to do so, or start up the downstairs gas-log (as he is likely to forget to shut it off)… so, of late, he just hasn’t used the main floor fireplace at all.

    Any thoughts or suggestions for me to try?


  4. Thank you very much for the very detailed description. there are many variables in your situation. I’m going to cut to the chase real quick here, the golden words to me were Madison, wi. I’m going to have you call Hansen and Sons and call Bill Husel, educated engineer, knowledgable about in-field wood burning equipment. here’s the phone number: (608)466-4185 make sure you talk to Bill Husell, one of the most extremely knowledgeable chimney people I’ve ever met. Btw, of the best explanations I’ve ever seen.

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