more secure thimble connection

[pybyr]

one of the things I need to complete on my initial install is my flue pipe- but to get it hooked up to my Econoburn as securely as I would like (I have an appropriate dread of waking up-- or _not_ waking up-- to a flue pipe that has come loose from the chimney), I'd appreciate some hints.

here's the background

my (modern) chimney has a dedicated 8" round terracotta tile flue for the wood unit, and the "thimble" for where the flue pipe goes in is a another piece of 8" round terracotta flue tile that was cut with a "fishmouth" and meets the main flue with refractory cement.

with my old wood/ forced air unit, I had a piece of 8" stove pipe with the crimped end stuffed into the 8" flue tile thimble, but even with some significant "enhancement" of the crimping to reduce the outer diameter of the metal pipe, it never went very deep (only about 3/4 inch) into the terracotta thimble, and I was confident of it staying there only because I had the whole flue pipe braced with several pieces of plumbing strap rigged so that the weight of the flue pipe pulled it towards the thimble

with the orientation/ layout I'll need to use with my Econoburn, that same arrangement of using the weight of the flue pipe to suspend itself to pull towards the thimble will no longer work

Anyone have any suggestions as to the best way to get an 8" metal flue pipe (which seems to have an inconveniently larger outer diameter than the inside diameter of my terracotta thimble") to reliably stay in the terracotta thimble, under all conditions of expansion, contraction, draft, etc.?

thanks

 

[Nofossil]

It's not elegant, but I've seen a section of plumbing strap pop riveted to the stovepipe and bolted to the cinderblock just above the thimble.

 

[pybyr]

thanks NoFo; after some more measuring and figuring, I think I am going to try some way to achieve a deeper/longer crimp on the snout of the pipe where it enters the thimble, and then try something like what you mention for belt&suspenders;. safe is better than elegant on this part of the install!

 

[Willman]

Trevor,I would take a leftover pc of the liner to a sheet metal shop and have a pc made up to slip in. They could open one end to accept your smoke pipe. Use an angle drill for some tap cons from inside of pipe to liner maybe. How did you make the fishmouth cut ? Was it a nice fit when done or was the refractory cement needed for filling in ?
Will

 

[pybyr]

Trevor,I would take a leftover pc of the liner to a sheet metal shop and have a pc made up to slip in. They could open one end to accept your smoke pipe. Use an angle drill for some tap cons from inside of pipe to liner maybe. How did you make the fishmouth cut ? Was it a nice fit when done or was the refractory cement needed for filling in ?
Will

great suggestions, Will- thanks-- I've fooled with sheetmetal enough that I might even try and succeed at doing something like that on-site with the abundant leftover sheet metal I have from other past projects

on the fishmouth I didn't build the chimney entirely by myself, 'cause I wasn't sure at the time whether I would really get it right or have enough time to do it all... I mixed mortar and carried supplies for the guy who really knew what he was doing, as a way to learn and save some $$$.

He used a skilsaw with a diamond blade to cut the fishmouths for each of the flues (I have 3 flues- oil, wood cook stove, and downstairs wood (used to be wood hot air and will now be the gasifier) and he basically did a series of small cuts at different angles to end up at an approximate radius.

He said he'd not used the refractory cement on past jobs (and this fellow has built a lot of really beautifully crafted chimneys) but I think he sensed my tendency that anything worth doing is worth over-doing, so he, on his own, showed up with the refractory cement and used it wherever the various pieces of terracotta met one another.

from the homework that I did at the time, apparently round flues "draw" better and more consistently than square or rectangular ones, due to the relation between the cross section and the surface area, and the absence of corners that end up being cold, slow pockets. obviously rectangular flues work, but I have been very pleased with the way that my chimney draws under nearly any reasonable conditions (unlike the burned out 1950s-ish disaster of its predecessor that got torn out, and that was old enough to be hopeless but not old enough to be historic, and would "stall" a draft- on a fire in progress- under some weather conditions)

 

[Willman]

Yes that is what I have been told on the round flues. Makes a lot of sense actually. They are not a stocking item at all masonry supply houses though. I wonder if a roto zip with a tile cutting bit would work on the tile ? I will definitely be using the round tiles when rebuilding my chimney. Just haven't tried various cutting methods. Drill bit around edge, saw blade cuts or maybe roto zip. A core bit that size would be a killer though.
Roll up some metal to fit the tile and then hammer up the inlet to accept your existing pipe. Buzz a weld down the seam and your good to go.

Will

 

[pybyr]

I wonder if a roto zip with a tile cutting bit would work on the tile ? I will definitely be using the round tiles when rebuilding my chimney. Just haven't tried various cutting methods. Drill bit around edge, saw blade cuts or maybe roto zip.
Will

the terracotta is surprisingly low density, so I expect any of the things you mention would work, as would a cutoff wheel in an angle grinder. If I were going to do it again I'd probably do the rough shape with an angler grinder and a cutting wheel, and then switch to a grinding wheel to form the final shape.

 

[CANUCK GLAZIER]

Hey Trevor,

With measuring tape in hand I would possibly try a 7" adapter to see if the fit might be a little better. Are you using double wall smoke pipe?

If this fails I would def go with fabricate on site method, it sounds as though you've had enough experience to get it to fit the way you want.

Rob

 

[Duetech]

one of the things I need to complete on my initial install is my flue pipe- but to get it hooked up to my Econoburn as securely as I would like (I have an appropriate dread of waking up-- or _not_ waking up-- to a flue pipe that has come loose from the chimney), I'd appreciate some hints.


Anyone have any suggestions as to the best way to get an 8" metal flue pipe (which seems to have an inconveniently larger outer diameter than the inside diameter of my terracotta thimble") to reliably stay in the terracotta thimble, under all conditions of expansion, contraction, draft, etc.?

thanks

If the pipe is single wall, take about 1' length, open it up and trim about 1/2" lengthwise from the male end tapering to 0" at the female end. Refit the pipe inter-lock and insert. To lock in place drill holes in the terracotta about 1 " in from the edge with about 3/16" mason bit and use 1" speed start sheet metal screws to secure pipe to terracotta. A small, 5-6" wide sheet metal band wrapped around the outside of the terracotta and held in place by large hose clamps before you drill the terracotta will increase surface strength and joint strength for the terracotta. OR Just remove about 3-5" of the 8" stove pipe male end inter-lock so you can taper fit it and insert into the terracotta and secure as stated above..Stay warm