Necessity of Block off plate...

Elisurfer4

New Member
Jan 7, 2018
64
Richmond, VA
y’all have really got my wheels turning so I’ve got posts goin all over, but here goes another...

The pro willing to do my flue install says that I will not need a block off plate in the chimney throat, and he is 99.9% sure :)rolleyes:).

I’m here to ask you practically pro folks the validity of this statement based on my situation.

I have a 26’ all masonry chimney and firebox on the exterior side of my home. The insert going in will be century cw2900 with surround and fan. An insulated SS liner will run from top to bottom of the flue.

Alright get at it guys.
 

Squisher

Minister of Fire
Nov 1, 2015
1,623
vernon BC, Canada
It is not required by code, but it will provide much greater heating performance. It's silly to not have one espescially on a exterior masonry install.

The installer is right and wrong. It's 100% not required but it 100% will heat better with it. Which is usually the whole point of the exercise in the first place.
 

HomeinPA

Minister of Fire
Jan 4, 2018
510
Central PA
It is not required by code, but it will provide much greater heating performance. It's silly to not have one espescially on a exterior masonry install.

The installer is right and wrong. It's 100% not required but it 100% will heat better with it. Which is usually the whole point of the exercise in the first place.
Agreed! And it doesn't need to be a "plate". It can be ceramic wool or the new noncombustible insulation who's name escapes me right now....:rolleyes:
 

Elisurfer4

New Member
Jan 7, 2018
64
Richmond, VA
Agreed! And it doesn't need to be a "plate". It can be ceramic wool or the new noncombustible insulation who's name escapes me right now....:rolleyes:
Are you referring to Roxul? How hard/pricey would it be for me to fabricate something and have it on hand when he arrives so that it’s as simple as him screwing it in whilst the install is underway?
 

redktmrider

Burning Hunk
Jan 21, 2012
196
Southern IN
How hard/pricey would it be for me to fabricate something and have it on hand when he arrives so that it’s as simple as him screwing it in whilst the install is underway?
I fabricated mine and installed it after the fact, I spent about four hours total ( I had to remove the insert and reconnect it).
Search for a block off plate, there are many examples. I would do it during installation as it will save you a large amount of time.
Also, if you have room, insulate behind the insert with Roxul, it will keep a lot more of the heat in your house.
 

Elisurfer4

New Member
Jan 7, 2018
64
Richmond, VA
I fabricated mine and installed it after the fact, I spent about four hours total ( I had to remove the insert and reconnect it).
Search for a block off plate, there are many examples. I would do it during installation as it will save you a large amount of time.
Also, if you have room, insulate behind the insert with Roxul, it will keep a lot more of the heat in your house.
Where did you take measurements for the plate?
 

HomeinPA

Minister of Fire
Jan 4, 2018
510
Central PA
Are you referring to Roxul? How hard/pricey would it be for me to fabricate something and have it on hand when he arrives so that it’s as simple as him screwing it in whilst the install is underway?
THAT'S IT!

You could try to prefab it but it's usually better to get the liner down there to see how it's going to lay in there in case something has to be "adjusted". That's why I like the insulation. You just pack it around the liner tightly and it doesn't go anywhere. Of course you don't want an entire pack of it sitting in your basement just to use 1/4 of a piece either so..... Maybe your installer has some?
 

redktmrider

Burning Hunk
Jan 21, 2012
196
Southern IN
If I remember correctly, mine is somewhat below the damper plate. My chimney had to have a few bricks removed in the damper throat area to allow the flex liner to come through, so don't make it fit flush to the damper plate. I had a local HVAC place cut it to size and make some bends around the edges to the surrounding brickwork so i could caulk it. Stuff roxul above the block off plate before placing it into position.
 

webby3650

Master of Fire
Sep 2, 2008
10,932
Indiana
All you need is some 26 gauge sheet metal. Take your measurements, then bend down 1” all the way around it, attach it to the brick through the 1” flange. I make the plate, then drop the liner, then measure for the hole that the liner will go through.

I just installed one in my COLD Fireplace. I insulated around the insert like was mentioned above. It took the whole bundle of roxul!
 

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weatherguy

Minister of Fire
Feb 20, 2009
5,756
Central Mass
Are you referring to Roxul? How hard/pricey would it be for me to fabricate something and have it on hand when he arrives so that it’s as simple as him screwing it in whilst the install is underway?
Not hard, that' what a few members have done, get the material now and it will be easier to cut the sheet metal down to size without the stove in your way.
 

Elisurfer4

New Member
Jan 7, 2018
64
Richmond, VA
The installer offered to install a $45 ceramic blanket around the damper, would that suffice as a block off plate or is it full necessary to make it metal?
 

redktmrider

Burning Hunk
Jan 21, 2012
196
Southern IN
The installer offered to install a $45 ceramic blanket around the damper, would that suffice as a block off plate or is it full necessary to make it metal?
The metal plate is better as hot air will still rise and move through the blanket, but the blanket is better than nothing.
 
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weatherguy

Minister of Fire
Feb 20, 2009
5,756
Central Mass
I would go to home depot and get a $10 shirt of metal and have it there before the install. You could precut and only have to cut out the hole.
 

DuaeGuttae

Minister of Fire
Oct 26, 2016
645
Texas
And then what else? Masonry screws?
Alternatively, if there’s metal all around where you plan to secure the plate, you can use welding magnets, I believe. I’ve not done it myself but that was supposed to be my summer project in my old home before I realized I’d be relocating. I think it was @weatherguy who gave me that idea, but I could be misremembering.
 

webby3650

Master of Fire
Sep 2, 2008
10,932
Indiana
We kind of settled on him cutting a piece out of the damper plate and then sealing that with ceramic blanket insulation.. will this work?
That would be ok in theory.. Almost always it’s necessary to remove a portion of the damper frame and a few bricks to get the liner down. It’s very rare that the firebox doesn’t need altered.
 

Markie123

Member
Jan 12, 2018
24
Orange,Ct
I am having a Voyage Grand put in next week . Reading all this very helpful information. I ask the install/salesperson. Insulation and this what he told me.

We do not put rock wool behind the block plate because it does not make much difference in stopping heat loss or air infiltration. As far as surrounding the insert it is not recommended and will void your warranty. It will cause the outside skin (convection chamber) to warp.

Any comments on this???
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
21,901
central pa
I am having a Voyage Grand put in next week . Reading all this very helpful information. I ask the install/salesperson. Insulation and this what he told me.

We do not put rock wool behind the block plate because it does not make much difference in stopping heat loss or air infiltration. As far as surrounding the insert it is not recommended and will void your warranty. It will cause the outside skin (convection chamber) to warp.

Any comments on this???
I will not pack around the insert for that reason. But insulation ontop of the plate does make a difference
 
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Mark8

Member
Dec 23, 2017
248
Central California
I am having a Voyage Grand put in next week . Reading all this very helpful information. I ask the install/salesperson. Insulation and this what he told me.

We do not put rock wool behind the block plate because it does not make much difference in stopping heat loss or air infiltration. As far as surrounding the insert it is not recommended and will void your warranty. It will cause the outside skin (convection chamber) to warp.

Any comments on this???
Very interesting because there are many threads suggesting to put Roxul or other insulation around the bricks in your exterior masonary fireplace to keep the heat from absorbing into the bricks, I wonder if this applies to all manufactures inserts and if the warranty literature mentions it.