Insulating Chimney liner - a new take

[Poncho]

I know there have been a quite a few threads about insulating, but our situation is a little different and wonder what some of you experts think. We live in an 1820 center chimney colonial. The house is designed and built to try and make the most out of the heat generated in the chimney mass, originally from the 5 fireplaces flues through it. I was considering running a new flexible liner (25ft) and leaving it uninsulated in the flue, and just insulating the top of the flue under the cap. The idea here is to capture as much heat in the chimney to radiate back through the house. I do understand their is a possibly of flow reduction due to cooling, but I'm thinking this should quickly slow as the chimney space heats up. Any one have any experience with this? the stove will likely be a Vermont Casting Vigilant. Poncho

 

[webby3650]

Does the chimney have a clay liner? In order to skip the insulation it would need to have a clay liner in good condition. If it's cracked the liner should be insulated.

 

[Poncho]

No liner, but the chimney is massive and functioning well.

 

[bholler]

It needs to be insulated. I am sure you have flamables in contact with the exterior of that chimney and if you do by code you need to insulate it intact liners or not. Also for many liners if you do not insulate them when using them for a wood burner it voids the ul listing.

 

[Grisu]

The idea you have with extracting more heat out of the flue gases sounds appealing but is NOT recommended with modern wood stoves. Those burn so efficient that the flue gases are essentially just hot enough to generate enough draft and to not precipitate creosote particles in the flue. Insulating the liner will make for less smoke spillage in to the room when you open the stove, less creosote, easier startups, and more consistent burns.

 

[BrotherBart]

If it is a brick chimney with no liner, not to mention over a hundred years old, insulate that liner. No question. Period.

 

[pen]

Yep, that sucker needs insulation. Been too many of these opened up over the years to find that by pure luck, the place stood for as long as it did when it is found that framing members / combustibles were actually built into the chimney in areas that could not be viewed........ And even if they weren't, as BB said, that sucker has paid it's dues, an insulated liner stands on it's own and in a worse case scenario, needs no support from the chimney to protect the home. Additionally, you speak of it being massive. That, in and of itself, means the idea of one appliance heating the structure up to a level that supports keeping the liner good and warm as well as adding heat to the home, is an impossible situation.

Line it, insulate it, sleep well, and enjoy the performance of the new stove. The original inhabitants of the home would be jealous.

pen

 

[fraxinus]

It would definitely be worth looking into a poured in place liner - SupaFlu or another system - for a chimney of this vintage. This kind of liner is self insulated, will fill any voids in the old mortar and brick and will add considerable overall strength to the chimney.

 

[bholler]

I have never been impresses with the durability of supaflues every one i clean sheds that material every time i brush it. And besides if you do that that means you can never change or add flues to that big chimney we have already put 3 liners in one big old fireplace chimney at three different times

 

[Nick Mystic]

Poncho,
Even if you use an insulated liner you could still try out your idea of utilizing the thermal mass of your big chimney to give off long slow heat. When you install the stove see if you can get at least part of it back inside your fireplace opening. Then go ahead with your original plan of sealing off the top plate tight (most of us use a generous bead of silicone caulk between the SS top plate and in your case, the top of the chimney opening). Don't install a block off plate at the bottom of the chimney and you'll have a good deal of the stove heat fill the chimney cavity to accomplish your goal of heating up that thermal mass of the chimney. I have a similar set up to yours, but I installed a block off plate because I wanted to capture as much heat as I could inside the house, but even with that set up my massive chimney (8' x 4' x 15' tall) heats up into the 90s and will still be quite warm long after the stove has burned out. If you find you need more heat inside the house, as opposed to heating your chimney you can always go back and install a block off plate without much trouble.
Good Luck.

 

[fraxinus]

I have never been impresses with the durability of supaflues every one i clean sheds that material every time i brush it. And besides if you do that that means you can never change or add flues to that big chimney we have already put 3 liners in one big old fireplace chimney at three different times

Very surprised to read this. I have had a SupaFlu insulated chimney for 15+ years. It's been cleaned each year and I have never seen any trace of the lining material in the little soot that comes out of the chimney. Once it's cured, the material is extremely hard. Different lining product? Faulty installation?

 

[branchburner]

We live in an 1820 center chimney colonial. The house is designed and built to try and make the most out of the heat generated in the chimney mass, originally from the 5 fireplaces flues through it.
The idea here is to capture as much heat in the chimney to radiate back through the house.

I had the same thought with my 1700s center chimney, but the amount of heat soaked up by the brick and effectively given back to the house is a drop in the bucket compared to the useful heat the stove will generate itself. A modern stove is a very effective space heater. It is quite different from heating with an open hearth in the 1800s, where burning in fireplaces 24/7 meant the brick mass would warm up and stay warm for months to help offset the fact that a fireplace is a horribly inefficient way to keep a house warm (warm being a relative term here).

In any case, as others note above, no clay liner = mandatory insulation. The practicality of using the brick structure as a heat sink is a purely academic discussion in your situation

If settlers of the 1700s and 1800s had been on their game, all these old houses we live in would have Finnish/Russian masonry heaters as their mode of central heating... THAT is the way to heat up a large mass and get a really worthwhile return from it.

Welcome to the forums!

 

[bholler]

Very surprised to read this. I have had a SupaFlu insulated chimney for 15+ years. It's been cleaned each year and I have never seen any trace of the lining material in the little soot that comes out of the chimney. Once it's cured, the material is extremely hard. Different lining product? Faulty installation?

I dont know if it is faulty install or not i know that the guy doing them in our area is a licensed supa flue installer. And the owner of golden flue has demonstrated his system for us at workshops and i know some of those have failed. I will say if done perfectly they are good systems but if the mix is a little wet or dry or it is to cold or to humid it can change things allot. I fell stainless is an easier generally cheaper and more consistent product. and the fact that it can be changed later on down the road is another benefit.