Flex liner a little short

[pgmr]

I am re-installing our insert into a different fireplace and the flexible liner from the old installation is a bit shorter than needed to exit the top of the chimeny in the new installation (about 10-12" short). Thought about adding an additional section of liner to get it to clear the top tile, then I stumbled upon this statement on page 6 of the Ventinox installation guide (http://www.protechinfo.com/mc_images/category/45/2050.pdf):

3) Masonry crowns with a clay tile and any UL listed rain cap
... Fill the gap between VENTINOX® and the tile with TherMix® and seal the last
inch with mortar or crown mix. VENTINOX® may be terminated anywhere within the tile, as long as it protrudes
at least four inches into the tile. Attach a UL Listed rain cap to the clay tile.

There is a picture in the pdf link above, but in essence, the liner ends short of the top of the uppermost clay tile, insulation (Thermix) is brought up to within an inch of the top of the metal liner, then mortar seals the last inch between pipe and clay tile. I have ss caps for both the 12x12" tile and the 8" liner. Am planning on poured insulation regardless.

Guess the questions are:

1) Will this adversely affect the draw (chimney about 14' to top of stove, center of house, higher than roof peak) vs having liner itself sticking out w/own cap directly attached?

2) Risk of freeze damage if water can pool in this cavity? If so, should the mortar be sloped toward the ss liner so that any rain water that gets by the cap or condenses on the cap and drips off will run down the liner?

3) Anyone installed this way? Happy with performance?

Thanks.

 

[jtp10181]

Never heard of doing that, but you can stick a rigid 12" or 24" SS piece on the top or bottom to lengthen it.

 

[pgmr]

Thanks, JTP, I've considered that. I would prefer to not see the liner above the clay tile, both for aesthetics and to prevent excessive creosote in the exposed, uninsulated liner.

Guess I'll just have to try it and see how it works. Worst case would require adding a small section of liner, ss top plate and drip ring.

 

[Hogwildz]

Some manufacturers make a coupler. In your case a coupler and the extra needed amount of additional liner to top. Also solves you sticking out the top ugliness factor.
They also make smaller sections of rigid, 6", 12" etc.

 

[pgmr]

The insert has been installed. It must weigh 450 lbs with doors off and baffle removed. Friend & I got it near the hearth via hand truck, up on about 6" of wood blocking, then used my floor jack to lift it. We then slid it off the jack and onto a piece of plywood protecting the hearth tiles. Used two 1/2" steel bars as rollers to position it back into the fireplace. Worked pretty well.

The liner was actually only about 4" shy of the top tile. I put in two 5 gallon buckets of homemade thermix (see https://www.hearth.com/econtent/index.php/forums/viewthread/15558/) to seal the block off plate area from loose insulation falling through. Filled the rest of the space around liner with loose perlite. Will put in a mortar seal between liner and clay tile when weather gets above freezing.

First fire last night and chimney seems to draw well - of course it was only 10F outside.