Heard a big thump the other day, and investigated up on the roof while blowing the leaves. Our chimney has a large slate top over the flue, and the noise from a piece of the slate breaking of and landing on the roof. From the soot in the crack I think it had been waiting to go for some time.
While up there, though I took a good look at the block off that the installers had put on last year, and was depressed by what I saw. They were back cleaning last week, & the guy mentioned that the liner had shifted, but he had "put some more silicone on it to seal it." What I found did not impress.
I have to say, I did not take a look last year after they finished the install--a mistake on my part. We have this enormous round flue on a large chimney, that has this large slate sitting up above on four rock "posts". (Slate can be lifted down for cleaning.)
To cap their install at the top, they used a large round piece of galvanized sheet metal (16 ga?--pretty light) with a simple collar, ran the liner through it and held it in place with some sheet metal screws. All they did to hold the assembly in place on top of the flue tile was to shoot a bunch of silicone on it--no mechanical attachment. Then, because there is not enough height to put a proper cap on the liner, they jammed some crumpled up screening into the end of the liner.
So after one season of burning the liner has shifted, and the piece of sheet metal has pulled off-center and off-plane. There are gaps between the sheet metal and the top of the flue, despite the cleaner's assurances that he had put more silicone on it (and there is a lot!)
Edited to add a pic of the chiimney
So what would cause the liner to shift?
How heavy should a reasonable block-off plate on the top be? Should it be mechanically fastened to the flue tile?
Does someone make a collar-style clamp that you could use to clamp around the round flue tile (I remember making large connectors for commercial round ducts with dad back in the day..) that could be mechanically fasted to the block off?
As usual, more questions than answers, and one more confirmation that if you want it done right, you might well have to do it yourself. (although in this case our insurers insisted on a "professional" install.)
While up there, though I took a good look at the block off that the installers had put on last year, and was depressed by what I saw. They were back cleaning last week, & the guy mentioned that the liner had shifted, but he had "put some more silicone on it to seal it." What I found did not impress.
I have to say, I did not take a look last year after they finished the install--a mistake on my part. We have this enormous round flue on a large chimney, that has this large slate sitting up above on four rock "posts". (Slate can be lifted down for cleaning.)
To cap their install at the top, they used a large round piece of galvanized sheet metal (16 ga?--pretty light) with a simple collar, ran the liner through it and held it in place with some sheet metal screws. All they did to hold the assembly in place on top of the flue tile was to shoot a bunch of silicone on it--no mechanical attachment. Then, because there is not enough height to put a proper cap on the liner, they jammed some crumpled up screening into the end of the liner.
So after one season of burning the liner has shifted, and the piece of sheet metal has pulled off-center and off-plane. There are gaps between the sheet metal and the top of the flue, despite the cleaner's assurances that he had put more silicone on it (and there is a lot!)
Edited to add a pic of the chiimney
So what would cause the liner to shift?
How heavy should a reasonable block-off plate on the top be? Should it be mechanically fastened to the flue tile?
Does someone make a collar-style clamp that you could use to clamp around the round flue tile (I remember making large connectors for commercial round ducts with dad back in the day..) that could be mechanically fasted to the block off?
As usual, more questions than answers, and one more confirmation that if you want it done right, you might well have to do it yourself. (although in this case our insurers insisted on a "professional" install.)