Adaptors have various lengths of “nose”. A long-nose adaptor can be useful as it adds "telescopicity" to the system (I think I just made up a word).

Do NOT use plasterboard of any kind inside the fireplace recess, even the pink fire-resistant stuff, as this is not allowed as plasterboard is not officially non-combustible (plasterboard okay on chimney breast though). Coat the board and the wall with copious amounts of the PVA adhesive to remove dust and prepare your surfaces (see PVA image). The attic scenario does not compare because you cannot have a sealed attic- there are always sources of airflow, and sources of humid air in an attic.

Introduction

Mark the center of measurement #1 in the center of this line, so there is enough room on both sides for total plate plus 1” extra on all side. Without an air source (open flue plate) condensation can't happen in a chimney because there is not a source for water vapor if it is sealed at top and bottom. Condensation just doesn't happen - condensation is carried by circulating air. I'll try to make it as short as I can. What I basically have is a question about Inswool being used to close up the hole in the flue after the rear of the damper (damper question below) was smashed out (by the installer), the stove was put in and Inswool and only Inswool was used to close the hole in chimney flue. The plate should be sealed around the edges of the stove pipe and have an access hate to enable the chimney to be swept.

Lets face the manufactures fudge the BTUs and areas that a stove will heat. They know more stoves will sell if the cost of installation is less. Telling an potential owner the cost just went up Measuring from this center line and on the line 1” in from the front, mark at 1/2 the measurement #1 in both directions (in the example, we would use 18” from each side of the line. Then make another mark at 1” past that line (or 19” from the center line).When the plate is inserted, it will hold itself up BUT, use a could masonry nails into mortar joints on both sides to make certain. No need to drive the nails all the way in, in fact just pinning is OK, cause they are easy to remove if needed. When you cut out your hole you can afford to have it a reasonable size. As long as it is smaller than the square and there is material left for the four screw holes to work then all is good. I would recommend that you first have the flue swept, then a capping cowl is fitted to the terminal/pot, which would allow the flue to breathe but prevent water ingress and birds from entering the flue. what is the method (at the top exterior of the chimney) one uses to support the weight of the liner and do you have any photos of this? Is there some type of "collar" you clamp to the insert with "ears" on both sides that you support on the outer edges of the liner?