Help on liner insulation

how tall is your chimney?

There is one school of thought that says the liner you have is only touching masonry in a couple of places, and is mostly surrounded by air. If that air column is capped off at top and bottom, then it can make a pretty good insulator itself, and thus other means of insulation are not necessary. I'm not saying it's right or wrong, just saying it's a theory I've seen posted.

They are correct that you can not insulate a 6" liner in that small of a chimney, it will not fit, they would have to bust out the terracotta then run it down. IF you have a tall chimney you could possibly run a 5.5" insulated liner down it.

If you want to deal with the thermix type of pour in insulation it would be a solution that wouldn't involve pulling the liner out. Many members here have done it, just remember it is pretty much a permanent thing.

The difference in liner heating due to blocking off room air with a blockoff plate is minimal. The liner is heated by the flue gasses, not the room air circulating up around the outside of the liner.

Rather than worry about potential for creosote, I'd install a block-off plate, run it for a season, and then inspect to see how it did.

I had considered Thermix for my situation as well, but hate the permanent nature of it. There's no going back, and when you have a 240 year old chimney you begin to think about what "permanent" really means, in the long run.

Not sure why you couldn't re-use the liner that you have. I have a very similar setup (8x13 flue, 18 ft. exterior chimney) and all the installer did was custom ovalize the liner before insulating (with 1/2" insulation no less) and everything fit fine even with the sloppy mortar joints in the flue. Then again, this guy knew exactly what he was doing and had all the right tools for the job.

On the other hand, if your stove if operating fine, maybe there's not much benefit in doing this now? +1 on installing the block-off plate though...but more to keep the heat from being lost up the chimney than to warm the liner.

I'm not an expert, but from what I understand the main point of insulating the liner when it's inside a masonry chimney is to cut down on creosote build-up. Since you've had it installed for a year I would start with the empirical data of how well your system is functioning. If it seems good and your wood supply is stable I would suggest monitoring the buildup. Insulation is nice but is not a substitute for all the other things we need to do correctly to keep from burning down our homes. I can still clog an insulated chimney (wet wood, smoldering overnight) if I want. Sweeping the flue 2x year vs one may be all that is needed.

If you're a suspenders+belt kinda person (as am I) you're not going to let it go, but I would suggest as others have done already that a block off plate top+bottom possibly paired with pour-in insulation may be a substantial enough upgrade and much more cost effective. Unless you've got a draft/excessive creasote problem my non-expert opinion is that pulling the liner and busting out the clay, then insulating + re installing is not going to gain you a margin of safety correlating with the effort involved.

But I'm not an expert. Just a homeowner who spends a lot of time over-thinking how to run an extremely simple appliance in my living room. Yes, it could be dangerous but so could that 3yr old jar of mayo in the back of the fridge.

Correct me if I'm wrong here but I thought insulating the liner was necessary for a chimney to meet code if there was any doubt the existing chimney is not built to code. I would think that severly offset tiles would indicate a chimney no longer meeting code. Again, please correct me if I'm wrong. I have Thermix poured in mine to meet code becuase my chinmey is about 90 years old and I had no clue whether it was bulit to code and wanted the piece of mind.

I have an exterior chimney and i have not had a problem one with creosote or perfomance with an uninsulated liner. I burn dry wood and check my chimney for smoke all the time.. No smoke equals no creosote,,, if you have smoke coming out of the chimney you run the risk of creosote build up,,, also burn hot through out the day for extended periods of time to keep chimney stacks hot. i did not need to sweep my chimney this year because I kept an eye on it. I have a non cat stove and if I see smoke I simply open the air controll on the stove until the smoke out the chimney is gone. I do use creosote powder from Menards during the heating season.

jqgs214 said:

Correct me if I'm wrong here but I thought insulating the liner was necessary for a chimney to meet code if there was any doubt the existing chimney is not built to code. I would think that severly offset tiles would indicate a chimney no longer meeting code. Again, please correct me if I'm wrong. I have Thermix poured in mine to meet code becuase my chinmey is about 90 years old and I had no clue whether it was bulit to code and wanted the piece of mind.

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There are different classifications. I think an insulated SS gives you a class A, which is nice but may not really be necessary inside a traditional masonry chimney. If a chimney can burn without a liner and be safe, a liner inside a chimney is doubly so. Besides, the point of the liner is not to keep the house from burning down but to correctly size the draft to the appliance.

begreen said:

I think code is that if the masonry chimney does not have a 1" air gap separating contact with wood then an insulated liner is required.

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Right idea, but I think it's actually a 2" air gap requirement. Just went thru this myself, and that's the number that was quoted to me.

what brand of flex? insulation is required on several brands of flex. also had one maker tell me they wont honor the lifetime warrantee unless it was insulated