Questions for chimney experts: Relocating thimble

We built our 28-year-old home with a double-flue chimney for a fireplace on the first floor, and the new Franco-Belge stove we installed in the basement. Per F-B dealer specs, the coal stove flue was built with 6" round terracotta liner, and loose insulation (vermiculite?) poured into the space between the round liner and the chimney block used to build the chimney.

Whoever built the chimney put the thimble through the block basement wall at a low height--39" from floor to bottom of thimble opening. I don't remember telling the builder I wanted it there, but it worked for the F-B, and of course I didn't think ahead to the day that I might want to burn another type of stove.

Our new DS stove has a much higher pipe outlet, leaving only enough vertical rise to the thimble to put in two 90* ells, with a short piece of horizontal straight pipe, with MPD, running from the second ell into the thimble. If you enlarge my profile pic a bit, you can see what I'm talking about.

For several reasons, I’d like to have more vertical pipe rise before the thimble. I’d like to have a cleanout at the bottom of the vertical pipe. I’d like to have a place to install a manometer and a baro damper (yeah, yeah, I know, but I think I want one anyway). I’d prefer the MPD be in a vertical pipe, not a horizontal one, so any ash dropped will fall to the cleanout, not lay in a horizontal pipe run.

My questions: How big a job is it to install a new thimble higher up the wall, and close off the existing thimble? Can it be done from inside (as opposed to dismantling the brick and block on the outside? Is this even advisable? Would the loose insulation have to be redone from the top of the chimney?

Thoughts and suggestions appreciated.

Wow....thats a tough one.
For the life of me i can not imagine how you could salvage the round clay line let alone the insulation.

If the chimney is sound (28 years old-should be fine)...have you considered eliminating the clay altoogether??...
Then add a new thimble higher.
What size are your chimney block btw?

How tall is your chimney and what does the stove "spec" for a chimney design ?
...you could always lower the floor area where the stove goes.......

Just plug the old thimble with cement and install a new one where you want it. Depending on the size about $20 at the brickyard. If you want it to look a little cleaner, bust the clay that protrudes from the foundation and then cement it off.

Mark where you want your new thimble, make the top 20" from the ceiling. and take a mason drill and drill holes as close as you can next to each other in circle bigger than the new thimble. You'll be going thru block before you get to the chimney. Knock that out with a hammer. Do the same with the chimney block, Be carefull not to break the clay liner. If the fill starts to run out just take some fiberglass and pack it in there to hold it in. Carefully drill the liner and knock it out. Slide the new thimble in seal inside and outside. Use the old thimble for a cleanout, Just get a smoke pipe cap and poke it in and put some concrete screws on each side so you can put heavy wire across to keep it from flying out from a puff back. Or just get a mason to come in and do it.

Few things I will point out, DS does not recomend a baro, they like hitzer say a MPD. With that said a clean out on a hand fed really isn't needed you are not putting large amounts of flyash up with a combustion blower like on a stoker.

If you want something real simple, put the mpd in the first elbow on the verticle section and the mano tap right below it.


Just my thoughts



Eric

Re. some of the questions above, here are two pics of the chimney:




Btw in that second picture, what looks like a smaller chimney near the roof peak is actually the neighbor's chimney.

Our chimney's roughly 30" deep (narrow dimension) and about 4.5 feet wide up where the double flue is. Not sure what the inside construction of the chimney is, in terms of block size. The terracotta flue liners are 6" round and 10" square. I took a bunch of pix when they were building the house, including some of the chimney construction--have the whole set here somewhere but haven't stumbled across'em in years.

The DS manual has only very general guidelines for the chimney, but based on some posts on here, it may not be tall enough for ideal draft. But it gets the job done, even on warmer days. And it's in good shape according to the DS stove installer. who inspected it.

Thanks for the guidance and tips, everyone. Probably won't tackle the job myself, but it sounds doable so i'll check it out this summer.

Eric, great idea about the MPD in the elbow. Hadn't thought of that.

Irrelevent to moving the thimble, but, I'm surprised that you get any kind of decent performance at all out of that stack. An exterior chimney which is too short for the roof it's above let alone the house. A proper stack, which will maintain draft during mild weather, and draft strongly during cold weather would terminate at least a few feet higher than the highest part of the home - that one doesn't come close.

My personal opinion... As long as you have any elevation to the thimble at all, why mess with integrity of the chimney by trying to punch another hole in it... ... What you have already should be plenty to work with.. I say scrap the idea of raising the thimble.

Great advise here... as lightning says, if you have vertical rise now i would have a hard time punching through for a new thimble, having said that... its not as hard as you may think and that other guy gave the proper way to attack this job by drilling and punching (everything gets cemented back in so it will look and function just fine). LOL @ the guy who sayed lower the floor (this had me rolling in laughter )

The more major concern i have with this Chimney is that upper roofline (as others have sayed), although it is far enough away to "get away" with it, this is a much more major flaw then your thimble location and the performance of anything and everything you burn in that chimney is effected (even though you dont realize it).

There are some easy options to extend the height of the chimney and then put a gosh darn cap over the terra cotta! You have a GREAT chimney & liner (arguably the best money and labor can buy!). Better yet cap the whole square to protect the cement between the brick and the terra cotta (or is you have the chimney extended have the mason build an arch as a cap (either would look fantastic with your style home).

Food for thought.... you say the chimney does work now, even though it's a bit surprising because gut instinct says it should be taller. Granting that it's an outside chimney, you are considering choosing to take 2 or 3 feet of it out of the heat? I'm voting to do nothing. IF you move the thimble up, because now 3 feet is cold instead of warm, it's possible that you change it from a chimney that works to a chimney that doesn't perform as it once did.

MarkV...

Lowering the floor was only suggested to get a chuckle out of everyone.....only dcrane saw the humor in it tho.....
with that said....heres a couple of things to consider:

Judging by the last 2 pics...others may argue its ability...but your chimney appears to be to code (of when the house was built)....and may work fine (or not even be improved upon by extending its heigth)...depending on the prevailing winds there
With that said...consider this.
The premise of relocating your thimble is simple...but in reality it can be quite an undertaking if you dont have some masonry experience. The one thing that will be to your advantage is that because you contracted the construction of your house...you should be privy to how it was constructed..
Not only do you need to penetrate your basement block walls..you will need to penetrate the chimney block as well. THEN you will need to put a hole in ROUND clay line to tie your new thimble to.
Heres my concerns.
From the pics....it appears your garage area has basement area under it (suspended concrete)...
I cant help but wonder if the block walls supporting it are "core filled" (not uncommon).
Secondly....as you mentioned...the flu is ROUND...6"...... which after you penetrate the wall...then the chimney...you need to penetrate the clay clay without compromising it too much. This is much easier said than done...and being round may prove to make it even more difficult..
I know things like this get done every day...but by qualified masons . Ive know idea of your skill level...and i am certainly not trying to discourage you by any means....but i am emphasizing that it is not "easy"

continued....

If you feel it is absolutey neccesary...i would suggest coredrilling your penetration. This would assure you the least amount of damage to the liner...and the cleanest of penetrations.
As far as your insulation...this may help too....as there is no risk of it pouring out until you remove the "plug".....
note....core drilling requires water....and can get messy.....fyi

Rigar wrote:Judging by the last 2 pics...others may argue its ability...but your chimney appears to be to code (of when the house was built)....and may work fine (or not even be improved upon by extending its heigth)...depending on the prevailing winds there

Berlin wrote:Irrelevent to moving the thimble, but, I'm surprised that you get any kind of decent performance at all out of that stack. An exterior chimney which is too short for the roof it's above let alone the house. A proper stack, which will maintain draft during mild weather, and draft strongly during cold weather would terminate at least a few feet higher than the highest part of the home - that one doesn't come close.

dcrane wrote:The more major concern i have with this Chimney is that upper roofline (as others have sayed), although it is far enough away to "get away" with it, this is a much more major flaw then your thimble location and the performance of anything and everything you burn in that chimney is effected (even though you dont realize it).

Yeah, 28 years ago, I was a total newbie at anything construction-related, and figured "a chimney is a chimney, and the builder knows how to build one." My father-in-law did the plumbing and electrical for us--he had much experience with oil and gas heating systems, so I'm sure he knew a bit about chimneys, but he didn't expressed any concern as he saw ours going up. I think Rigar's right--the chimney likely met code back then--but just barely. I was sorta shocked when, several years later, I began reading up on chimneys and saw the general guidelines for chimney construction, esp. re. being taller than the 2nd floor roof.

But, we've burned both our F-B and the DS through some pretty warm, damp, zero-wind days with temps in the high 50s, and haven't had problems. I'm careful, though, to open the MPD a bit more to let more hot gas up the flue, which I think helps avoid draft issues. The one issue I do have, which may be partly due to the lack of height, is that when the chimney is cold, and there's little to no wind, it strongly downdrafts. If I'm lighting the stove on a day like that, I always warm the flue first with a hairdryer. That's another reason I'd like to have a baro, that's where I used to insert the hair dryer nozzle.

Two things probably help the draft when the stove's burning: the front of the house faces almost due north, and winds are usually from w/nw so they're seldom sweeping over the 2nd floor roof toward the chimney--though we occasionally do get ne/e/se winds during coastal storms, where the winds swing around as the storm passes. But even that's never caused an issue while we've been burning.

Also, the chimney is 24 feet from the two-story part of the house.

I do plan on getting rid of that tall evergreen near the chimney this summer--that could cause issues as it gets taller. Besides, it's starting to interfere with the coal truck backing in to deliver, so it's gotta go.

Btw, that other flue for the fireplace has never been used. I told my wife when we moved in, I wouldn't build a fire in it until we got glass doors, and she's never found a set of glass doors she felt looked "colonial enough" to install. Classic hubby/wife impasse. That fireplace is as clean inside as the day we moved in.

looking at the pics the chimney is fine it is much more than 10 feet from the next highest point that being the house roof...i would just leave the thimble alone and work with what u got...if u go a cutting and bust up ur clay flue liner u got real problems/lot of work to fix...i have built hundereds of chimneys in my 50 plus year bricklaying career, and i would just work with what i got if it were mine...but anyhow good luck...