Can I use an old un-lined chimney as a chase for Class-A metal chimney? (cast-in-place not an option

[nscarnati]

I have an old house (1880) with a large un-lined chimney (18"x18" inside dimensions) that is a straight shot down to the firebox, no bend of anything. I cannot find any cast-in-place chimney installers in my area (I called supaflue, goldenflue, etc to get a reference, and they all said they had no dealers in my area - balitmore, md) so I was wondering if I could just use the existing chimney as a chase for a 2 or 3 wall metal class-a chimney.

I originally intended just to use a metal liner with insulation, but there are some missing bricks halfway up that are unrepairable without ripping down the entire chimney (which is not an option), and using a liner would put it too close to the combustible materials outside of the chimney where the bricks are missing. That left me with thinking my only options are a cast-in-place, which again I can't find anyone to do, or else use a class-a chimney, and treat my chimney as a chase since it's plenty large enough to fit the 6" ID chimney. There would be no/minimal heat transfer from the chimney to the brick. Since you can use a class-a chimney through a ceiling and attic, I would think that the heat transfer from a class-a chimney is minimal as compared to a metal liner, making it safe to be put in my chimney, close to combustibles (where the bricks are missing).

Am I off-base here, or is this something that is reasonable, and most importantly SAFE to do? I was planning to install a block-off plate with insulation (kaowool) at the bottom of the chimney, a couple inches above the bottom end of the class-a chimney.

 

[karri0n]

This is what most people do. My only worry is those missing bricks. Is it possible to put anything in that place like a metal plate, fill with mortar, something like that?

 

[nscarnati]

This is what most people do. My only worry is those missing bricks. Is it possible to put anything in that place like a metal plate, fill with mortar, something like that?

i bet u could replace the bricks & seal them with a caulk tube of stove mortar [cheap @ HD], then drop an insulated liner...

Nope - it's about 10' up the fireplace, and 15' down from the top. Even if I could find someone small enough to fit in an 18x18' chimney I would want to take the risk of them climbing into a 100+ year old chimney and something potentially dangerous happening.

 

[nscarnati]

class a needs 2" clearance to combustibles & is expensive so i'd talk to local fire dept for cheaper option...good luck.

I could put the chimney closer to the opposite side of chimney with there full brick is missing, so I think I could easily get by with a >2" clearance to the combustibles. The expense of getting class-A I priced out to be only about $300-400 more than buying an insulated rigid liner.

 

[TreePapa]

Do you have an alternate location for the stove? Perhaps you can leave the historic fireplace alone and install the stove with a completely new chimeny, as if you didn't have the FP at all? Put some candles or electric logs in the old FP.

Peace,
- Sequoia

 

[oconnor]

It may be cheaper to repair the chimney thru the wall of the house when compared to doublewall Class A chimney. I wouldn't worry about weight - so long as you can install a support of the equivilant to the bracket they use, you should be fine. Those wall brackets aren't much.

Compare the cost of cutting a wall in the house to access the chimey and repair and reline to the Class A option. Remember - if you have an old flue, which you do, code will require a Zero clearance install on the liner, so you will need to insulate the liner, which will add cost (you did mention your intent to insulate anyways). You should only need to patch the holes, as the flue integerity will be the liner and insulation. You may want to consider one of the preinsulated systems like the one Simpson sells - it is essentially downsized Class A, but as a liner.

 

[webbie]

To answer the question, I think you could do this with regular HT. The main thing is to use a brand with a stainless exterior and also to support it correctly. That means support from the bottom as opposed to from to top.

It could be lowered from the top into a support which was somehow fastened into or near the bottom of the chimney - perhaps a TEE, or else a ceiling support, depending on exactly what you have there.

But, yes, it can be done and it will be very safe.

I would also have sheet metal plates with a hole in them every 10 feet or so in order to keep the chimney relatively centered. These could fit loosely and be attached as the chimney was dropped down.

It might be wise - assuming it is OK by the chimney manufacturer, to use ss rivets where the sections meet.

Note that some chimney might be MUCH lighter in weight than others, so that may help also.