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Community and Q&A

Options for removing an unused chimney?

michaelbluejay | Posted in Green Building Techniques on

I know it’s best to remove our unused chimney because
(a) We lose conditioned air.
(b) Vent fans cause backdrafts.
(c) It’s a huge thermal bridge.

I think my options are:

(1) Remove the exposed portion above the roof, cap/seal it, install new roofing at the hole.  Most effective but most expensive.

(2) Simply cap the top of the flue.  Easy and cheap, and stops air, but still have the thermal bridge.

(3) Install a “vented cap”.  The website of Black Goose, a chimney contractor in VA, says that unused chimneys should be “capped” but still vented:

“Though capping your chimney will block some of the drafts, it won’t stop all of them. That’s why it’s important to vent your capped chimney.  One way to do this is to install a chimney cap with a built-in vent. These caps allow air to flow freely while keeping out animals and moisture.”

This makes no sense to me.

After capping the chimney, I’m thinking of building out the fireplace into a small cabinet/closet.

Thoughts on all this?

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  1. Expert Member
    Michael Maines | | #1

    #3 is interesting; I can see that if there are small holes in the chimney, the stack effect will result in air leaks. I have done both #1 and #2 for myself and clients, and recommend #2 when possible. Even better, take it all the way to the basement and get "free" space.

  2. paulmagnuscalabro | | #2

    I would second Michael here; I am halfway through removing the now-unused chimney at my house, and the extra 2' x 2' on two floors + partial basement is going to be well worth it. On the upper level I'll patch in the floor, and on the main level I'll be installing storage cabinets.

    For what it's worth, I took the chimney below the roofline and then hired a roofer to patch the hole. It made me die a little inside to hire out such a small job, but I was glad to have it done in a couple hours and to not be going up and down a 12:12 metal roof. I'm using a Makita demolition hammer to bust things apart, then carrying out the bricks in buckets. Messy but not too much work.

    1. Expert Member
      DCcontrarian | | #3

      "Messy but not too much work."

      That is exactly my experience. I've taken down a fair number of chimneys and never had one that resisted coming apart. Usually all it takes is a tap with a hammer to loosen a brick. Often a bigger problem is keeping the whole thing from toppling over once you start.

      Resist the temptation to toss the bricks to the ground, that's dangerous and makes a mess of the yard that's hard to clean up. For the section above the roof, I like to drop the bricks down the chimney so I can deal with them when I get off the roof. Once through the roof, all the work is either standing on the ground or at worse a stepladder, I prefer to take the bricks out and carry them out of the house in buckets. Because the inside of a chimney is going to be covered in soot, and the old mortar will be basically sand, this is the messy part. I spring for a big box of contractor bags, line a 5-gallon bucket with the bag, fill it with bricks and then tie off the bag.

      Best is if you have two people, a "clean" person and a "dirty" person. Dirty person takes the bricks and loads them into buckets and ties off the bags, clean person carries them through the house and out to the dumpster.

      I would take it down to at least the building envelope, which is the floor of the attic if you have a vented attic. Most of the time if it's worth doing it's worth taking down to the basement and reclaiming the interior space.

    2. Expert Member
      DCcontrarian | | #4

      "For what it's worth, I took the chimney below the roofline and then hired a roofer to patch the hole. It made me die a little inside to hire out such a small job."

      I've paid roofers to take the chimney down below the roof, and was shocked at how little they charged to do that -- a few hundred dollars -- as part of another job. Probably less than it would have cost me to get rid of the bricks. They take tons of debris to the landfill every day and know how to handle it efficiently.

      1. DennisWood | | #7

        "For what it's worth, I took the chimney below the roofline and then hired a roofer to patch the hole. It made me die a little inside to hire out such a small job."

        I did exactly that, except the roofers also took the chimney down. They took it down about 8' to the attic floor, and patched the roof. The sprayfoam "flash and fill" we did in the attic after sealed the chimney "stub" at the attic floor so the three stories of unused brick chimney is now completely within the house envelope.

        I found an air chisel (although intensely loud) will pop a brick in about .5 seconds. Chimney that has been protected inside the home (where mortar is out of the elements) will be more difficult to remove.

  3. quietone | | #5

    Yep, agreed with the other commenters here. Chimneys come down easily. Take it all the way down to the basement floor. On retrofit projects I've then used the reclaimed space to run the interior ducts for an HRV/ERV from the basement mechanical room to the attic for ceiling supply and returns.

  4. michaelbluejay | | #6

    Thank you all for the replies. The main reason I wanted to remove the chimney was that it wasn't functional (always released lots of smoke into the house when we used it, even with an open damper and a window cracked), so it seemed pointless.

    However, I just ran across a product called a "fireplace insert". It's kind of like a wood-burning stove that you insert into your fireplace, with its own special duct that runs up the chimney. The advantages vs. a regular fireplace are:

    (1) It's got a heat exchanger that sucks in room air and blows hot air back out.

    (2) House doesn't get smoky. The air that goes through the heat exchanger isn't exposed to the wood-burning part.

    (3) Minimizes the amount of make-up air lost up the flue.

    If we lose power during a winter storm, this seems ideal for making sure we don't freeze. Just need a battery-powered backup to run the blower fan in the insert.

    1. Expert Member
      DCcontrarian | | #8

      That still doesn't solve the problem of the building science disaster that a masonry chimney is. You still have a big unsealed and uninsulated hole in the middle of your house.

      I'd be thinking about taking the existing chimney down to the attic floor, the going through the building envelope with a modern chimney.

      1. michaelbluejay | | #9

        You don't think it can be adequately air-sealed?

        Yeah, it's a thermal bridge, but so are windows, and I have some of those, too.

        I'd like to keep it as a backup source of heat in case we have another Snowmageddon like we did a few years ago, where much of the city was without power for days. Battery backup for a single mini-split for 2 days' of kWh is very pricey, and I'd rather not burn fossil fuels in a generator (plus the pro installation of a transfer switch would cost). Fireplace insert will also cost, but it seems like the easiest solution for emergency heat.

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