Flue/thimble question

Hi there,

I have questions about my chimney and I'm hoping to get some opinions before I go much further with things here. Sorry if this post is too long or I get rambly but it seemed like a bit too much is better than too little when it comes to details...

My layout:

I have a single flue, masonry chimney in the middle of my house. It's made up of 16" square concrete block and lined with 8" round clay flue tile in what I believe is good condition. The thimbles are both in the basement and that's where my current and hopefully future stove will live. The house is a two story cape and the chimney exits adjacent to the ridge so I'm going to guess that the flue length is about 30' give or take a foot or two. It has two thimbles but I have no intention of ever using more than one at a time. They are on different but adjacent sides of the chimney, one at 56" from the floor, one at 32". The thimbles are 7" which seems odd to me but I'm not particularly wise in the ways of these things. I know that it was a pain in the butt finding a thimble plug for the darn things and that most of the hardware out there is 6" or 8".

What I'd like to do:

I have an unknown vintage Vermont Castings Vigilant. I inherited it with the house and have burned it a fair amount over the last handful of years but it has developed a fairly nasty crack in the outside cast iron which I think renders it unsafe, the back plate in the firebox is also badly warped, this all combines to make it burn nearly uncontrollably. So... it's on the way out. I did spend a little bit of time considering a Tarm boiler rather than a stove and haven't fully ruled it out but after thinking it through I'm currently leaning pretty heavily toward just putting in a new stove based on reduced complexity and cost compared to the Tarm. The one that I've been looking pretty hard at is the Woodstock Fireview based on the good reviews here and the fact that they make them 50 miles upriver from where I live.

Because of some orientation changes to the space in the basement I'd like to use the low thimble (32" off the floor, facing north) rather than the higher thimble the VC has been using all along (56" off the floor facing west). One of the things that I've done in the basement was to break up the large mass of rocks that the previous owner had piled up around the chimney. In this pile they had an 8" flue tile mortared onto the 7" thimble so until I dug into that I had been mistakenly under the impression that I was 8" from bottom to top but that unfortunately isn't the case. Also, before I knocked the old rock pile down I had no idea there was a lower thimble in the chimney, it had been completely covered by the rocks so that was a bit of a surprise.

As part of my changes in the basement I'm building a partition between the finished space where I'd like the stove to be and the unfinished space where the chimney will stay. The new partition will require a short run of flue between the face of the wall and the thimble, the finished wall surface willl be 14"-16" away from the face of the chimney where the lower thimble is (the one that I'd like to use). I know that I need to take combustibility into account when working some sort of new flue through. My current thoughts are a fair amount of Durock and whatever necessary spacers I need to hold the Durock off the wood etc... but I'm not 100% sure just what kind of parts I need to get through the wall and into my oddball 7" thimble. I'm also willing to build a box around it or do whatever else it takes to get the stove hooked into the flue in a reasonable and safe manner so all suggestions welcome.

My questions:

- What kind of parts do I need to get to my oddball 7" thimble through the new partition to the edge of the wall for hooking up to the stove? I'm assuming that if I had a 6" or 8" thimble I could use some sort of through-wall insulated adapter and then just follow those instructions. Although, even if I did have a normal sized thimble I'm still unsure about which parts because I haven't seen direct applications for those to attach to masonry thimbles (but that's probably my ignorance showing through rather than a lack of the right stuff for the job). I'm also willing to build up something completely out of masonry but I'd probably prefer to just buy a pre-fab and save the time if it's an option.

- Even if my clay flue is in decent if not perfect shape should I consider pulling a 6" stainless liner down there to make the transition through the thimble nicer? It's a straight run flue and I'm quite handy so I have no particular qualms about doing it (other than the cost <g>), just no interest in doing it if there's no sense to it.

- If I use the lower thimble will I need to be particularly careful in the way that I block off the upper thimble? Whatever I use there to block it will certainly be subject to a good bit more heat than the lower one saw when I was using the upper. Probably pulling a new liner would make this a non issue but again if I don't have to pay for that I'd just as soon skip it.

I'll gladly provide more info, pictures or diagrams if they'd help at all. Thanks for any help or thoughts (and for reading this far)

Dan

Thanks Franks, I appreciate the reply.

Is class A generally sized to make up nicely with single wall stainless or would I have to fudge something together do you think? I do a fair amount of metal work but have nearly zero hands-on experience with any of the flue stuff so sorry if that's an ignorant question. I guess I'd then cut the 24" class A flue pipe down to whatever it needed to be in order to make up properly with the thimble adapter and mount it to the wall which would be somewhere less than 24" away from the chimney.

As far as the inspection door goes, I didn't explain it very well but the chimney and the thimble will be open to the unfinished space on the other side of the wall. Access won't be wonderful because there will be a 4" lally column in the middle of a 10" gap but plenty of space for a flashlight and a mirror to let me see all around the interface and also lots of ventilation to keep heat build-up to a minimum. I gave a good bit of consideration to moving the wall toward the chimney so that it would be run flush which would negate a lot of this stuff but there are some structural and plumbing constraints that pushed me in this direction. The wall is only a few studs right now though so I can easily change the way that it's made even if I can't move it so bricks or metal or really anything is an option if that would help.

I don't have a good handle on prices but just for the sake of hand waving that's maybe something in the $125-ish range for the 24" class A, $85-ish for the through wall thimble, $75-ish for the stove pipe adapter and maybe $50-ish for the short bit of single wall for a total in the $335 range? Talking about the prices mostly to make sure we're talking about similar parts and I'm not completely off base ;') And I think that I'd be looking at buying all of those parts to get through the wall even if I pulled a new flue liner down since I'd have to come off of whatever stuck out of the tee at the bottom of the liner with something similar to get past my combustible constraints so it's not like I can partially justify a liner based on saving any of this stuff. Although, I'd probably pull a 6" liner so does it make sense to do this with 6" class A and adapt it one way or the other at the thimble? That way I could re-use everything from the class A out through the wall in the event that I did have to re-line at a later date. Maybe that's just trying to cheap out but I figured I'd ask...

Thanks again,

Dan

Franks said:

You dont cut class A. I figured a 24" to get you thru your wall and about 6" into the room. If it is a little more than 6", you dont cut it, you just deal with it. Class A isnt designed to have a section of single wall stainless attached to the male (top) side, but it can be done. It may require a little fudging.

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Yeah, okay I was afraid of that ;')

Not that I won't do it that way but it's one more thing that I need to think about I guess. Mulling a lot of things over...

Franks said:

As long as you can view the connection with the class A, single wall stainless and your thimble easily, thats fine.

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Okay, that part should be okay then.

Franks said:

None of my suggestions ever take pricing into consideration. There's tons of other folks on here who will spend days to find way to do things cheaper (and not necessarily worse) Hell, some even save 10 bucks a year making their own fire starters. Hopefully with this bump in the thread, one of those folks will chime in with a possible cost saving alternative to your chimney issue.

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Fair enough. I put the pricing stuff in there because I'm so darn ignorant of all the parts in play here that I wanted to make sure that I was in the ballpark on the parts list, not to complain about how expensive it was. I'm definitely interested in doing it properly and safely.

I have another thought to throw out there. If I were to build a non-combustible box back from the wall surface to the chimney face could I just run double wall stove pipe to the thimble? To visualize what I mean, you'd see the surface of the wall and then there would be a rectangular 'hole' in it, probably lined with durock (or tile on durock or something) with the masonry thimble at the back of the 'hole'. I could probably make the hole something like 20" wide and about as tall as necessary. That would still give me 6" or thereabouts on both sides of double-wall stove pipe which I think would be okay. Does that seem like something worth fleshing out in more detail or am I missing some important bit of badness in there?

Thanks,

Dan