Block off plate and liner cap?

[sbowers22]

I am installing a new fireplace insert and ss liner. I would like to know the procedures for making and installing a block off plate and also the liner cap at the top of the chimney. I will have about 5 or 6 feet of the liner insulation left over to use where best needed. As far as the the block off plate is concerned I would prefer the easiest material to work with. Since the insert has a shroud around it, it will not be visible. The liner manufacturer recommended just stuffing some of the leftover insulation in the damper area. Would that be good enough if the top plate is also insulated and sealed?

 

[begreen]

That's a common shortcut. The problem is that it rarely seals the flue well. Most folks make a block off plate out of common 24 ga sheetmetal. But there is a kit out there if desired. Have you had a chance to read these articles?

https://www.hearth.com/econtent/index.php/wiki/Why_damper_seal_is_needed/
https://www.hearth.com/econtent/index.php/articles/making_a_block_off_plate/

 

[tickbitty]

I have just checked out that article prior to my own insert installation... should the plate also be insulated? We will have most of the old damper intact as it's a vestal damper forming a continuous roof to the fireplace. So really all that will have to be blocked will be the area around where we cut the damper to get the insulated liner through, and the long, 4" high slot that formed the old damper hole. I assume we should still make the whole plate to fit, but should it also be insulated somehow or is metal sealing in there good enough? I have a really big flue, a foot square, so the insulflex liner will probably only fill about 8" or so. And/or should the top plate be insulated? If so, with what cause I am not sure if rockwool is available in regular stores.

Sorry don't mean to hijack, just searching this same thing out myself. I am having a handy friend help with the install but he is not accustomed to doing installs!

 

[newstove]

I used this to make an insulated block off plate for the bottom of my insert. Works nice, and not very expensive either. I used the 1" thick.

http://www.anvilfire.com/sales/k_index.htm

 

[tickbitty]

Thank you...
I wonder though if there's anything else I can use, since I want to try to get this before Sunday! Ulp....

 

[EatenByLimestone]

Pick up a piece of sheet metal. Any heating supply place will have it. Last piece I picked up was 3 ft by 2 feet and cost around 3 dollars.

Matt

 

[tickbitty]

Pick up a piece of sheet metal. Any heating supply place will have it. Last piece I picked up was 3 ft by 2 feet and cost around 3 dollars.

Matt

Thx Matt, I assume I can find the sheet metal, I was concerned about finding something appropriate to insulate it. Kaowool and other specialty materials don't seem easily had from box stores or on a weekend/short notice! Need the sheet metal be insulated?

 

[cycloxer]

You could fab up your sheet metal panels and add the insulation later. Just don't screw the panels in yet. You don't need the insulation right away to run your stove.

 

[sandie]

My guy is going to do mine in the next week or so. I want to know how this should be done. My install was done with a plate at the top so now will he cut tow pieces and an half circle in each to surround the pip or should it be one piece with a hole cut in it for the pipe(that would be hard to get the circle perfect now that pipe is in chimney etc. How much Kaowool on top like an inch, 6 inches etc.? It should be fit like a glove right? Below where the fireplace damper was? Why not on the same ledge of the old damper since he knocked the damper out of the fireplace chimney. I do not want to see it when sitting in my fireplace room, I want it to totally prevent the heat of the woodstove from going up the chimney. How thick is 24 ga steel like 1/2" or 1/4" or inch thick. I want it right and he said he has never been asked to do one before, everyone is satisfied with the top plate but feels confident in doing it. I want it right finally.

Is the plate steel or stainless steel or cast iron or is that a dump question? I am thinking steel so it can be cut but thick enough to not let the heat through and with the insulation should do the trick.

 

[michaelryba]

I didn't end up making my block-off plate as exact as the article. Like you, I didn't have a ton of room to fill. I just wedged 1-2" of the insulation in; cut two peices of sheet metal with semicircles in the center. I used some high temp sealant to secure the peices & fill gaps instead of trying to drill holes in bricks.
Since your chimney is sealed at the top as well, this doesn't need to be a perfect fit with lots of insulation. It just deflects the radiant heat from your stove & first foot of liner back into the room. I think it matters more in an insert stove application; so you don't have to run the fan as high to harvest every last btu from the stove before is goes into the sides of your chimney.
One installer I talked to before doing this myself said he just wedges the insulation in there and referred to that practice as a "soft" blockoff. By the way, guage of wire & sheet metal is simply how many would fit in an inch. So 24 guage metal is 1/24 of an inch thick. The higher the number, the thinner/smaller the peice.

 

[cycloxer]

Make your plate out of stainless or regular sheet steel. Avoid aluminum or galvanized as they are not a good choice due to the high heat environment. You could use 22 gauge, 24, 26 - it doesn't much matter. You can either make it in one piece or two side pieces - whatever best fits your situation. You want to insulate above the plate with 1-3" of fireproof insulation - something like Kaowool or Rockwool or Rockboard. I used 2" thick Rockbard 60 or both my lower plate as well as the upper one at the chimney crown. You can secure the plate by wedging it into place and screwing it into the mortar joints with Tapcon screws. Seal it along the perimeter with high temp silicone, Rutland clear or red. If you search the forums you can see variations on the theme.

The block-off plate really seals off your fireplace smoke box and chimney from the rest of your house. It works exceptionally well to keep the heat in your house. It will pay you back for years. It also acts as a safety device (fire door) should you have a chimney or flue fire.

My supplies:
22 gauge sheet steel painted black with 1200°F stove paint
2" thick Roxul Rockboard 60, gives an R value of about 8
Rutland Clear 500°F silicone
Tapcon 3/16"x 1-1/4" self-tapping masonry screws