Hairline cracks and heat transfer

[mattmania]

Quick question...if I have some hairline cracks in my chimney, how big of a deal is it for heat transfer to the combustible exterior (plywood) wall of my house? I have a new flex steel (with titanium) liner which I installed, and old ceramic liner within a 4 in masonary chimney, which is an exterior chimney (three walls of the chimney outside the house). The chimney is not in bad shape. I fixed some hairline cracks (say no more than 1/8 inch) on the exterior walls of the chimney, but there were not too many. I am just concerned about the face of the chimney I cannot see (the one adjacent to the exterior wall of the house). Assuming some of the same kinds of cracks exist there, is that an issue?

 

[bholler]

is your liner insulted? If not do you have the required 1" of air space between the outside of the masonry structure to the house? If not then yes cracks or not you could have a problem with heat transfer but the cracks would make it worse

 

[mattmania]

is your liner insulted? If not do you have the required 1" of air space between the outside of the masonry structure to the house? If not then yes cracks or not you could have a problem with heat transfer but the cracks would make it worse

The liner unfortunately is not insulated with fiberglass insulation because there was already a clay liner installed and the steel liner could not be fit with insulation. So just the steel liner. There is about an inch or so airspace I believe between the exterior wall and the chimney though.

 

[bholler]

The liner unfortunately is not insulated with fiberglass insulation because there was already a clay liner

well you would not want fiberglass there but if you have the required space it should be pretty safe if not you need to insulate it

 

[mattmania]

well you would not want fiberglass there but if you have the required space it should be pretty safe if not you need to insulate it

I dont mean fiberglass...I mean that special fiberglass-like sleeve that goes onto steel liners these days with wire mesh, etc. Thing was, when the liner was installed, to put that sleeve on would require 7 and 1/8 inches of spaces...since there already was a clay liner, we only had 7 inches. Plus the chimney was tall and so it would have been impossible to slip down a liner with sleeve since the inevitable minor imperfections that an older chimney always has (excess clay mortar on clay sleeve here and there, slight microscopic bends of chimney here and there).

I do have about an inch between the chimney and the house...maybe a touch less and it is an exterior chimney, so actually you can feel a slight draft between the chimney and the house wall (which is probably a good thing, considering any heat radiating off of the chimney would be cooled down by the cold winter air before it becomes a problem to the house. But if it did want to insulated the liner itself, how would I do it? Assuming the sleeve wont fit, perhaps slipping a high perlite to cement mixture down the face of the liner facing the exterior wall of the house would do the trick, even if I can only get 1/2 inch or so down there as a buffer, might be better than nothing. Or maybe I can just try it out as is, and be very observant first...not run the stove at night just yet, etc. Any thoughts?

 

[bholler]

But if it did want to insulated the liner itself, how would I do it?

Take out the old clay liners in cases like yours we do it every time

 

[mattmania]

Take out the old clay liners in cases like yours we do it every time

Right, okay...well since it does seem I have that 1 inch of airspace, I think I might be set. I will just check that the steel liner itself has a little airspace between the clay liner and itself...then I am guessing I am all set. Taking out the clay liner seems like a lot of work at this point, and maybe unnecessary, assuming I have the 1 inch between the house and the chimney, as well as some airspace between the steel liner and the clay liner, eh?

 

[bholler]

Right, okay...well since it does seem I have that 1 inch of airspace, I think I might be set. I will just check that the steel liner itself has a little airspace between the clay liner and itself...then I am guessing I am all set. Taking out the clay liner seems like a lot of work at this point, and maybe unnecessary, assuming I have the 1 inch between the house and the chimney, as well as some airspace between the steel liner and the clay liner, eh?

I personally would do it anyway for the performance gains but as far as safety goes you should be ok as long as you have that 1" the entire length of the chimney

 

[mattmania]

I personally would do it anyway for the performance gains but as far as safety goes you should be ok as long as you have that 1" the entire length of the chimney

Right, well maybe I will do it one day...but for now not too concerned with performance. The one inch does run the entire chimney. It is an old house I should note...so that one inch is actually between the chimney and cedar (or some kind of) wood shingles of the exterior wall, not vinyl shingles like modern houses have. I am hoping that doesn't change things, does it?