I was trying to hang a shelf on the wall in my living room and was drilling holes to plug fishers in it. Accidentally I found myself drilling into part of the flue of the fireplace (people living in the apartment below me have one). The hole dapth is less than one inch and I immediatly changed the position of the shelf.

The drill didn't actually pierce all the way through the flue wall as I can clearly see the bottom of it.

Is this condition dangerous? Should I warn the people living below me? I want to fill that hole, what material should I use? I don't think I actually went all through the flue fall, but would this cause the part around the hole to overheat?

Thanks for the help.

  • 1
    I am guessing you have a brick fireplace. it should be at least 2" thick and then a fire brick liner of 1-2" many of the of the flues I have worked on have been thicker than this by 2x on single story and 4X on multiple story.
    – Ed Beal
    Jun 14, 2016 at 13:01
  • @EdBeal yes it's a cancrete fireplace (or bircks) I couldn't actually pierce it all the way inside, I just started drilling and then, noticing the drill didn't go much deep in the wall I stopped and noticed the darker color of the wall behind the paint. So I looked on the roof and noticed the chimney for the fireplace. (no other apartment in the store has a fireplace and the chimney is very small and hidden by trees). Jun 14, 2016 at 13:20
  • 1
    Only going an inch is no big deal ! The hole can be filled with fire clay or mortar. No steel is needed and steel would cause more problems than fire clay or mortar (They use mortar to build the flue, and fire brick and fire clay to make the burn box area). I used to clean chimney's and have done some repairs (Clean sweep Chimney service in Sonoma county Ca. My dad owned that and several other bushiness before passing).
    – Ed Beal
    Jun 14, 2016 at 14:23

1 Answer 1


First of all, yes the condition is dangerous. You have compromised the integrity of a part designed to protect you from smoke and toxic gasses that are released by combustion. Released into a relatively confined spaces these bad gasses can accumulate and pose health hazards. Carbon dioxide and carbon monoxide are your primary concerns here.

But you haven't put the people below you in any danger. You've put yourself in danger. The gasses will be releasing into your unit, not theirs.

Since this is an apartment you should first notify your landlord of the issue. You will be responsible for the repairs, so you can offer to fix it yourself, but your landlord has the right to know of the damage and risk and you have a legal and ethical obligation to inform him.

For repairs, you'll need to open up the wall to get access to the flue. Then you can patch the small hole with metal (MUST BE METAL) tape - this is available at most box stores and is specifically designed for sealing metal ductwork.

  • thanks a lot for the reply! I think the flue is made in concrete as it's very hard. Also the hole didn't actually pierce through the flue wall as I can clearly see the bottom of the hole I drilled so I guess (hope) no gas would come out form there. I'm concerned about the heat compromising the integrity of the flue in therms of overheating or possible cracking. Jun 14, 2016 at 13:22
  • 2
    If the flue is concrete (entirely possible) and you are certain you didn't puncture it, then you have little to worry about. The stone / concrete used is not going to expand / contract enough because of the heat to be a danger. Jun 14, 2016 at 13:39

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