Exterior chase rebuild for wood stove

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jesse72

New Member
Jul 17, 2023
28
Sparks, NV
I am nearly finished with a long project in which I removed an old FMI 42GC zero clearance fireplace and built a shallow alcove for the installation of my Hearthstone Mansfield 8012. I will put a link to that at the bottom.

My chase is 26' tall on the outside of the house, with about 17' of flue. I removed the old double wall air gap flue that was for the FMI because it was not rated for a wood stove. I replaced this with Class A DuraTech insulated double wall 6" pipe using their ceiling support box to transition from black pipe to class A.

The pictures will tell the story but it was not an easy project to say the least!

1. I removed the siding from the back of the chase for access to the flue. In was lucky to borrow 20' of scaffolding from a family member!

2. The second story was insulated with the pink fiberglass you can see, that is a bathroom with a tiled shower on the other side of the insulation.
- I used 5/8" type x sheet rock to protect the insulation even though it was farther than the 2" clearance that class A pipe requires.

3. I used rock wool insulation to insulate the entire chase, including the top of the fireplace "ceiling". Since I had the siding off I used thick metal wire stapled to the studs to hold the insulation on until I could vapor wrap and side it again.

4. I built a fire stop at the 8' mark with double 5/8" type x sheet rock and made my own metal transition piece to ensure a 2" clearance from the drywall.

5. I was unsure if I should ventilate the chase with some side vents and decided against it, I didn't want to let the cold air into the chase. Otherwise why insulate it.
** if that is something I should have done, let me know!!

6. My brother in law is bending a new chase cap for me out or stainless steel so I am waiting on that still.


Let me know what I did wrong lol!

The first pictures are of the chase and flue when the old fireplace was still installed.

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I'm in the midst of a similar project, but ironically I tore out my stove to replace with a ZC. Here's a link to my thread:


Did you fire caulk at the 'ceiling' penetration? It looks like there is still a small air gap around the pipe in your picture. I haven't seen where it is recommended or not recommended to caulk this penetration, but I planned on caulking these areas on my project to completely seal off between interior/exterior.
 
I'm in the midst of a similar project, but ironically I tore out my stove to replace with a ZC. Here's a link to my thread:


Did you fire caulk at the 'ceiling' penetration? It looks like there is still a small air gap around the pipe in your picture. I haven't seen where it is recommended or not recommended to caulk this penetration, but I planned on caulking these areas on my project to completely seal off between interior/exterior.

Thanks for asking, and your project looks great! The ZC you are installing looks nice, I bet that will heat nicely.

I did not add fire caulking, I believe you are referencing my fire stop that is about 8' above the alcove ceiling. (see photo below)

I basically made a rough metal pass through because I did not want to wait for one to ship from DuraTech. I think there is about a 1/4' gap maybe and didn't feel the need to seal it completely.

I almost wanted to leave a 1-2" gap actually, so that that area of the chase could vent into the area above it and then through the chase cap venting. As to not trap hot air in that section. But I ended up not doing that after all, but am slightly concerned about that area not venting at all

Hope that answered your question!

IMG_8404.jpeg
 
I was able to finish the project by adding a custom made 16ga stainless steel chase cap that my brother in law made for me at his fab shop. It is probably over kill but I am ok with that!

I made it about 1/2" wider and longer than the chase in order to allow the chase to vent as per DuraTech's manual saws and I also added spacers under it to raise it about 1/4' off the chase top.

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I'm in the midst of a similar project, but ironically I tore out my stove to replace with a ZC. Here's a link to my thread:


Did you fire caulk at the 'ceiling' penetration? It looks like there is still a small air gap around the pipe in your picture. I haven't seen where it is recommended or not recommended to caulk this penetration, but I planned on caulking these areas on my project to completely seal off between interior/exterior.
Typically, the firestop sleeve is about 1/4" larger than the OD of the chimney pipe. That ends up leaving a 1/8" gap which could be caulked with good silicone, but it's not necessary. Flat, stove glass gasket could also be used.
 
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I also replaced my ZC with a wood stove, a drolet myriad. Also pulled the original air vented flue, but was able to accomplish everything by climbing up in the chase, which was 2' x 4' dimension. Also, my chase was truly exterior to the house, which is how a chase should be built. So, I just ran my class A 6" right up, braced at two locations, paying special attention to the black pipe transition and fire proofing and sealing and insulating that. Ended up great.
 
I also replaced my ZC with a wood stove, a drolet myriad. Also pulled the original air vented flue, but was able to accomplish everything by climbing up in the chase, which was 2' x 4' dimension. Also, my chase was truly exterior to the house, which is how a chase should be built. So, I just ran my class A 6" right up, braced at two locations, paying special attention to the black pipe transition and fire proofing and sealing and insulating that. Ended up great.
Its impressive that you were able to do that from inside the chase! I initially thought I could but it seemed too tight to do it all. Maybe if I didn't do all of the mineral wool insulation and fire stop. Taking the siding off was a lot of extra work but I don't think I could have done it any other way.

I wish it had been a masonry chase so I could just use a flexable flue liner!
 
Its impressive that you were able to do that from inside the chase! I initially thought I could but it seemed too tight to do it all. Maybe if I didn't do all of the mineral wool insulation and fire stop. Taking the siding off was a lot of extra work but I don't think I could have done it any other way.

I wish it had been a masonry chase so I could just use a flexable flue liner!
I think you will come to appreciate the benefits of a good insulated SS chimney, especially if you burn a lot.
 
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I think you will come to appreciate the benefits of a good insulated SS chimney, especially if you burn a lot.
Thanks and yeah so far its been nice to have a the flue stay warmer and not worry about cold flue starts!
 
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