block off plate at top...fiberglass below???

What they are calling a block off plate is the top plate for the liner install. Standard stuff. A block off plate goes at the bottom to keep that hard earned heat from rising and getting absorbed into the chimney instead of the living space.

Their "block off" at the top of the chimney is probably part of the cap anchor plate that is bent to the shape of the flue tile.
Insulation under that plate is a good a idea, & I did it on every liner install. They should also install a block off at the bottom that
is insulated as well. The theory is that the lower one will allow the insert to heat up quicker & begin radiating that heat back
into the room. Without the lower plate, the entire masonry assembly, including the chimney, has to heat up before you start
getting heat in the room. The insulation at the top & bottom will create a pocket of "dead" air between them, which will also
act as insulation in the chimney. Tell the installer you want one at the damper area as well as the top.

I have used unfaced fibeglass in the damper area without any issues, much to the chagrin of many members here.
If enough of it is crammed up in there, it won't fall out, & it works very well.

Do not use fiberglass it can melt i have seen it. Like everyone else said they are referring to the top plate. But i would insist on an insulted liner and a block off plate on the bottom. That is how it should be done and if they wont do it find someone who will

And make sure they use the proper insulation for the liner not just shove fiberglass down the top and up from the bottom that is not the right way to do it.

Not gonna argue with you, bholler, but I've never seen it melt & I installed & serviced for 11+ years.
When I pulled my Regency 3100L after 5 years of burning, the pink insulation had turned a yellowish
color, but it had not melted, & the only area that had turned was in direct contact with the SS Liner.
The owner I worked for has been in the business since 1979 & in fact, wrote most of the NFI Wood
Burning Certification course final exam questions. He directed that we use the unfaced fiberglass.
His business & his reputation were on the line with every install his crews did.
I will take his knowledge & expertise over the combined knowledge here,
but different strokes for different folks.

DAKSY said:

wrote most of the NFI Wood
Burning Certification course final exam questions.

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I am sorry but there is no where in the nfi or csia certificaion tests or literature that sayd fiberglass is ok anywhere in a chimney system. You might get away with it but why when you can buy ceramic wool that is tested and approved for the application. Or roxul that is at least rated for the proper temps. And the owner i work for (my father) has been in business since 1977 and has never and will never use fiberglass in a chimney

Like I said "different strokes"...I'm done with this one..

DAKSY said:

Like I said "different strokes"...I'm done with this one..

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I agree that there are many different ways to do things. For example i think every liner should be insulated fully regardless of whether it meets code with out the insulation or not and i will agree that i am going above and beyond what is actually required there. But there is no way that stuffing around a liner with fiberglass meets any code or manufacturers directions. And therefore i think it is irresponsible to tell anyone it is ok to do so.

A block-off plate is always extra. It takes more skill and labor to do this. That list is a pretty average way of installing particularly on a bid competitive job. The downside is there are details that get overlooked or passed by such as creating a drip edge by folding over the top cap sides, using Roxul instead of fiberglass, and installing a damper-sealing block-off plate. If this is an interior chimney installation then the lack of the block-off plate is not that big a deal. If it is an exterior chimney, then installing a lower block-off plate may help the insert retain more heat. The metal plate will do a better job at preventing stove heat from going up the chimney than stuffing the area with a breathable material. Some folks that also have room behind the insert have insulated the rear wall of the fireplace in order to retain more warmth around the insert. This would likely be a DIY project.

It would be best to ask them for a quote. I'd estimate it will take them an extra hour (shop time included) at their going rate. If you opt for it, insulating the back of the fireplace (if there's room) is a DIY job that should be completed before they start the install. Just be sure there's room behind the insert to accommodate the insulation.