Chimney liner insulated below the block-off plate?

[RickBlaine]

I decided to go with an insulated 6" flex liner made of stainless steel because I will only have one gentle bend and the bend is barely 22 degrees, not 45, not 90.

Does the liner have to be insulated through and below the block-off plate? It will only be about 8 inches between the block-off plate and the top of the stove, by the way.

My exterior-wall brick chimney is 10 feet tall from the block-off plate to the top. I do plan on buying some sort of 3-foot solid extension pipe to add to the top to bring my total chimney length (bottom of stove to exhaust) to the required 15 feet. Does this extension also need to be insulated?

Thank you!

 

[bholler]

no it doesn't need to be insulated it wont hurt if it is either though. you could always try it with out the extension first in some situations they can work fine on a short stack if you do need to extend it use a section of insulated chimney if it is un insulated out in the open like that it will probably get allot of buildup in it.

 

[jatoxico]

If you are installing in an existing masonry fireplace then I would say no (can be uninsulated below block off plate). You can stuff Roxul or use furnace cement to seal the gap between the liner and the plate after install.

In an existing fireplace I would also fill the smoke chamber with Roxul to minimize air movement before you install the block plate.

 

[RickBlaine]

no it doesn't need to be insulated it wont hurt if it is either though. you could always try it with out the extension first in some situations they can work fine on a short stack if you do need to extend it use a section of insulated chimney if it is un insulated out in the open like that it will probably get allot of buildup in it.

Thank you for the rapid response....

As for the extension, I will see if I can pick up a 3-foot insulated solid pipe and connect it somehow (I am certain they sell a connector from flexible liner to solid) to the rest of the system.

I would rather just do this once...since I have to be up on the roof anyway. I figure go for 15 feet rather than stay at 12 feet. The manual says minimum should be 15 feet....

 

[RickBlaine]

If you are installing in an existing masonry fireplace then I would say no (can be uninsulated below block off plate). You can stuff Roxul or use furnace cement to seal the gap between the liner and the plate after install.

In an existing fireplace I would also fill the smoke chamber with Roxul to minimize air movement before you install the block plate.

Thank you, I figured on some sort of insulation as that smoke chamber is large. Pulled two "flat as a pancake" raccoon carcasses out of there when I bought the house- and promptly installed a lock-top damper on it.

 

[bholler]

Yeah there are specific extension plates made by most class a chimney manufacturers. I understand just doing it once to I just like to try to avoid the look of that extension if possible but that is up to you it will probably work better with it on there.

 

[RickBlaine]

My 3-foot chimney extension will be a shiny stainless steel beacon on a hill! Actually, on a roof but you get my point.

 

[jatoxico]

Thank you, I figured on some sort of insulation as that smoke chamber is large. Pulled two "flat as a pancake" raccoon carcasses out of there when I bought the house- and promptly installed a lock-top damper on it.

Oh nice!

Prior to properly installing my block off my smoke chamber was unisulated too. It took more than three full bats to fill that space alone. At the level of the chamber I used to measure >80 F on the outside brick at about 25-30 F outside temp. After I am now at about 45 F. Not perfect but a whole lot better.

 

[RickBlaine]

Oh nice!

Prior to properly installing my block off my smoke chamber was unisulated too. It took more than three full bats to fill that space alone. At the level of the chamber I used to measure >80 F on the outside brick at about 25-30 F outside temp. After I am now at about 45 F. Not perfect but a whole lot better.

Thank you! I did not think of that! I am a firm believer in the adage "You can't manage that which you cannot measure", so I love to do before/after evaluations. Don't think the raccoon carcasses were providing much insulation in their state of dehydration. I will have to actually measure the smoke chamber and figure out how much I need. It is cold in there....

 

[Hogwildz]

Yes insulate the liner, no not below thew block off plate, keep that heat in the house.
Use proper insulation, not fiberglass.

 

[RickBlaine]

@Hogwidz: Thank you sir, I shall do that.

I did come across a couple of posts here where members used Micore to fashion a block off plate instead of a thin piece of sheet metal. Any discussion or should I stop trying to reinvent the wheel and just use sheet metal?

 

[rwhite]

Micore will work as a block off plate, Problem is that it's not very strong, As you try and work it into place it may fall apart, and it may sage with no support across the bottom. . It's pretty much like working with compressed newspaper. I would stick with sheet metal if possible.

 

[RickBlaine]

Thank you, rwhite.

The well-written instructions posted here on the forum specifically call for sheet metal, but I saw a few posts with people "getting by" with Micore. I'd rather do it once and do it right....metal it is!

How to make a sheet metal block-off plate for a masonry fireplace: https://www.hearth.com/econtent/index.php/articles/making_a_block_off_plate/