Masonry Chimney Thimble - What Does Correct Look Like?

[funbaker10]

Hello Everyone.

I have a wood burning central furnace that vents into a masonry chimney.  The chimney was constructed out of concrete block with a clay/ceramic tile lining.  The chimney has three separate clay tile lined flues of which one is being used for the wood furnace.  The other two are for two separate open fireplaces.  

When I installed the wood burning central furnace about eight years ago I vented it to an existing penetration into the chimney.  It has been working OK but the existing penetration into the chimney is quite low relative to the outlet of the furnace.  This results in a rather shallow pitch of the connecting pipe between the furnace exit and the chimney.  To improve this situation I want to make a new penetration into the chimney about 32" higher than the original.  

I have been gathering as much info as I can off the internet and watched as many videos I can find but still have some questions.  I want to do this "right" and want to meet code, etc.  My main questions are these:
1) Does a clay/ceramic thimble need to be mortared in through the chimney wall penetration?
2) if yes, what type of mortar is required?
3) Is modern practice to use a clay/ceramic thimble or have things changed (metal thimbles?)
4) Does the connecting pipe then go all the way through the thimble or does it simply connect to the thimble?  
5) If the connecting pipe goes through the thimble is it OK for the connecting pipe to contact the thimble?  Does it rest on the bottom of the thimble?
6) In my case the stove connecting pipe is 6" in size.  What should the ID of the thimble be?

Any experience or info you might be able to share would be greatly appreciated.
Thanks.

[Bruno of NH]

The clay thimble needs to connect with the clay tile with refactory cement. That is code in NH.
It can be mortared in to the cement block or chimney block.

[funbaker10]

I assume refractory cement is just a special high temp mortar which is mixed up in a similar fashion to regular brick mortar?  I also assume the "mortaring" of the clay thimble to the chimney liner is done reaching through the thimble with a 2 or 3 inch "puddy" knife.  Lastly, the stove connector pipe then goes through this thimble until it is flush with the inside of the clay chimney liner?  Does the stove pipe just sit in the thimble loose?

Thanks for the help.

[Al_Smith]

Quite frankly a clay lined flue is probably okay for a fire place but could and does create a creosote problem on a stove or furnace .
I discovered I had such a problem and no amount of cleaning alleviated the problem .The flue was built for a fireplace and not for an "air tight " insert .It produced creosote that looked like road tar .The type that will catch fire .
A single wall stainless steel pipe installed in the clay liner corrected that problem .Installation of same was not a problem as it was only 14 feet .

[Bruno of NH]

Refractory cement is prefixed like furnace cement.
Masonary chimneys work best inside the building,they get better draft with less build up.

[funbaker10]

Hi Everyone,

I need to make a new penetration into a masonry chimney to give my wood furnace connecting pipe more pitch between the furnace and the chimney connection.  You may have seen a separate thread I started a couple days ago about some questions I have regarding this new penetration through the concrete block with clay liner chimney.  As I ponder the new penetration details, a few more questions come to mind.

I know that it is common for a metal chimney pipe to be inserted inside the flue of a masonry chimney and used as the vent pipe for a wood burning appliance.  My question is, when this is done does the metal pipe have to be "Class A" chimney pipe?  Since the masonry chimney with clay liner is already an approved "Class A" chimney, I'm thinking there would be no good reason why the metal pipe running inside couldn't be single wall pipe.  

I'm thinking just install a piece of 6" schedule 10 stainless steel pipe inside the existing clay lined chimney flue.  Then make a nice, easily disassembled connection between this pipe and the connecting pipe from the furnace.  If needed the pipe could be disassembled from the connecting pipe, pulled out from the top of the chimney, cleaned and reinstalled relatively easily.  

Thoughts?

Thanks in advance for any advice.

[Al_Smith]

The stuff I used was 22 gauge I purchased through a building supply not a so called stove shop which would have been twice the price .It was 7" which fit nicely in the 9" clay liner .At all the joints I used stainless steel pop rivets which trust me are a lot harder to crimp than steel rivets .Actually about couldn't hardly get-er-done .I had about 200 bucks in 14 feet .
It dropped into a hole in 3/16" steel plate in the top of the existing fire place opening .Worst part of the job was moving the plate steel Lopi insert I figured weighed 6-700 pounds .I had to get a little creative to get that done .The top 4-5 feet where the existing brick chimney goes above  the roof has fiberglass insulation stuffed between  the stainless  liner and the existing clay liner .The only portion that creosotes  at all is the top 5-6" above the clay liner where it's exposed to air which is in a form about like carbon which won't burn .
I normally run a brush through it at the beginning of the heating season and pressure wash the stainless steel grilled cap .About a half hour start to finish .It's getting about time to  do that job as a matter of fact .