Thimble question

[gorsuchmill]

I received an estimate to reline a masonry chimney in which the installer plans to remove a 22" long clay thimble and simply turn a 90* with the flexible SS liner towards my boiler. He is not going to install a replacement thimble. I have two questions:

1) is a thimble necessary when the pipe is passing through a masonry/stone wall?

2) if the thimble isn't necessary, should there be an air gap around the horizontal part of the T, or should it have insulation or refractory cement to fill in the void?

3) wouldn't a T be preferred to the 90* at the bottom of the flue?

Thanks for your help.

Lee

 

[pybyr]

OK, I should say up front that I am not a pro at this topic, but had one chimney re-lined with SS, and helped build another from the ground up, and I did a fair amount of the design and construction myself after having researched it a lot.

I am puzzled how your installer could do a 90 degree without a tee unless you are installing a relatively small liner in a relatively huge existing flue (in which case you are darn smart to be putting in a liner- and you should insulate it)

Depending on what wood-burning appliance you plan to hook to the liner, I would be concerned about the ability to clean the SS liner if it is a one-piece with a bend at the bottom. That seems likely to prevent through-brushing if you will be using anything that might deposit any degree of creosote or soot on the inside of the liner

_If_ you are going to be using a wood gasifier boiler, and plan to have adequate heat storage and otherwise operate it so that you rarely "idle" and create crud that could accumulate in the SS liner, then the "continuous bend" elbow you describe _might_ be OK as long as you pull the smoke pipe between the boiler and vacuum out any accumulated ash every now and then. But I'd never go with such an install with any other system that might deposit creosote or soot in the liner.

That's my $0.02, guaranteed to be worth at least $0.005