Questions on insulated flues/chimneys

[op_man1]

Hope someone has this info:

1 - What is the r-value range of an insulated flue (metal liner)?

2 - I have a masonry chimney with an uninsulated metal liner inside it. We are renovating the house and in doing so will be adding 2 inch foam (R10) on our outer walls. I am wondering if insulating the outside of our masonry chimney would have the same effect as insulating the liner.

Cheers
François

 

[Pagey]

I would venture to say, maybe, yes and no. Yes, in that it MIGHT help keep the flue gases warmer like an insulated liner. But in my mind, it would NOT afford the protection offered by an insulated liner. In the event of a chimney fire, in theory, the insulated liner would (help) prevent the chimney fire from igniting anything inside the masonry portion of the chimney.

Smart people will soon correct me if I am wrong. :coolgrin:

 

[oldspark]

If you did have a chimney fire that foam flash burns does it not, but I do think it would help but not might be recomended. In a nut shell I knew a guy who's chimney was crap and he enclosed it in a frame work and insulated it, worked like a champ after that.

 

[op_man1]

If you did have a chimney fire that foam flash burns does it not, but I do think it would help but not might be recomended. In a nut shell I knew a guy who's chimney was crap and he enclosed it in a frame work and insulated it, worked like a champ after that.

Code requires that the masonry chimney be a certain thickness before combustables come in contact with it - I do believe that it is made of concrete blocks and that it would be safe to have combustables against the blocks. In any case, will check code for required non-combustable thickness.

Interesting that you know someone who did this and that it improved performance.

 

[oldspark]

If you did have a chimney fire that foam flash burns does it not, but I do think it would help but not might be recomended. In a nut shell I knew a guy who's chimney was crap and he enclosed it in a frame work and insulated it, worked like a champ after that.

Code requires that the masonry chimney be a certain thickness before combustables come in contact with it - I do believe that it is made of concrete blocks and that it would be safe to have combustables against the blocks. In any case, will check code for required non-combustable thickness.

Interesting that you know someone who did this and that it improved performance.

If I remember correctly he had haydite chimney blocks and he was dipping cups of water out of the bottom of chimney every day, after he put the frame work around it there was no more water and he had to cut down the air going to the stove other wise it would over heat due to the better draft, this was an old air tight stove.

 

[oconnor]

You can't place a combustible against the brick unless you have a zero clearance liner installed - that is one that is insulated to remove the clearance requirements. Insulating the brick will certainly retain heat and allow the chimney to work better, but in the event of a chimney fire, you could have the fire breach the chimney and cross into the structure because of not respecting the clearances.

 

[SWNH]

In the event of a chimney fire, in theory, the insulated liner would (help) prevent the chimney fire from igniting anything inside the masonry portion of the chimney.

I don't get it. What's to burn on the inside of the masonry part of the chimney?

 

[Pagey]

In the event of a chimney fire, in theory, the insulated liner would (help) prevent the chimney fire from igniting anything inside the masonry portion of the chimney.

I don't get it. What's to burn on the inside of the masonry part of the chimney?

Yeah, I should have elaborated on that. Most chimneys were used before being lined, and even with a good sweeping, it's impossible to remove all of the deposits on the clay liner (or brick, if there was no clay liner). With an uninsulated liner, if you have a fire inside the liner, it can and will get hot enough to ignite the deposits remaining on the clay/brick of the original flue. In fact, I think there was a thread here where that very thing happened. No, the brick won't burn, but what's accumulated on it sure will.