Blockoff plate: how to attach a larger patch piece to the plate, which is already in place?

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yuryk

New Member
Feb 17, 2024
54
Eastern MA
In preparation for my unit installation, I'm learning how to make a block-off plate myself (huge thank you to this community for so many helpful posts!), coz installer keeps saying it's overkill.

Step 5 from the instructions for the Block-off plate construction (thank you again!) says:
If the liner is coming into the firebox at an angle or you are concerned about fitting, you can cut a bit larger rectangular hole in the block-off plate, then cut a larger patch piece that has the hole for the liner. This will provide some adjustment room to get the liner aligned correctly with the stove. (C alternate)

blockoff plate.png

I'm making the plate myself in advance and should have everything ready for the installer, so I want to make a bigger hole as suggested - just in case we have to move that oval adapter during installation.

Question: when the liner is aligned correctly, how to attach that larger patch piece to the block-off plate, which is already in place? I won't be able to hold a nut on the other side...

Just in case: this is how the oval-to-round adapter will be routed (green lines) and where the plate will be situated (blue line). I have already cut a cardboard:
Blockoff plate: how to attach a larger patch piece to the plate, which is already in place?
Blockoff plate: how to attach a larger patch piece to the plate, which is already in place?


Thank you.
 
Last edited:
I really don't know about the big picture and how working with the installer will go, but as far as attaching the small plate to the big block-off plate, two options are threaded holes in the big plate (if it is thick enough to cut threads), or rivets. Riveting with a rivet gun is very straight forward.
 
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Patch piece on top then high temp RTV or rivets but it really doesn’t need to be a structural connection. It will be hard to drill with the patch on top. (Won’t be easy with the stove there anyway)
 
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The blockoff plate doesn't have to be down low, it only needs to seal off the damper area.

I'm a bit confused about this approach. Is this the only adapter that can be used for the insert? Does the 12x12 chimney tile come in at an angle or is it straight above the damper area so that the frame could be cut for a straight shot up? If so, why is DuraLiner being used at all when flex liner is being used for the chimney?

Can a hole be notch-cut in the damper frame to make this a fairly straight-up install with a standard flex appliance adapter connecting the insert?
 
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Thank you guys!

Patch piece on top
Brilliant! I guess that's the best way. Thanks!

blockoff plate doesn't have to be down low, it only needs to seal off the damper area.
Makes sense. I will make the plate a bit more narrow to place higher.

Is this the only adapter that can be used for the insert?
Well, another alternative was to not use any adapters and remove few bricks. But when I asked if there is an option to keep fireplace box intact as much as possible, the installer said that oval-to-round will work perfectly with my damper opening.

Does the 12x12 chimney tile come in at an angle or is it straight above the damper area so that the frame could be cut for a straight shot up?
It's like this:
IMG_3697-.jpg
Damper 1.jpg
Damper 2.jpg


why is DuraLiner being used at all when flex liner is being used for the chimney?
So for the chimney liner I ended up ordering "EasyFlex 316Ti Pre-Insulated Chimney Liner Kit - 6" from Woodland Direct instead of "BEST-Flex Liner Model L" since that one was not insulated. I guess the oval adapter is used so that we don't have to remove the bricks for the liner to get through... The installer said that my vertical damper is only 4 inch wide, so it's going to be pretty challenging even with the adapter. That's actually the reason he does not want to deal with the blockoff plate, but rather put a damper sealing kit around the oval (vertically, in that damper opening, rather than horizontally below it) OR use mineral wood in the same damper space, but again - not horizontally like I want and like you guys recommend.

Can a hole be notch-cut in the damper frame to make this a fairly straight-up install with a standard flex appliance adapter connecting the insert?
I guess it can't because of that shift that's visible on the photos above... But I'm way less experienced than you guys...
 
I took out the whole damper and metal frame. It’s never going back to an open fireplace as long as I own the home. After that it’s not my problem
 
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