# Block off plate . Do I really need it?



## Dmitry (Jan 26, 2015)

Just learned from another thread that some of the most knowledgeable  guys like Grisu, Begreen, Hogwildz recommend to install block off plate even if stuffed insulation being put in place already. My install was not easy, I had to remove some bricks, ate a lot of dust while laying face up in a firebox. So standard block off plate was not an option for me.( I think so). So, I just stuffed  Roxull as much and as tight as I can in a chimney around pipe.  So, now I'm thinking about going back and making some kind of block off plate.
Just wondering what are the physics behind need of block off plate added to a lot of tight stuffed Roxull installation. 
 I also stuffed Roxul  at the upper part of chimney under cap as low as I could. The flue is cemented to the insert. Not sure if I can move it due to packed insulation.
  It's gonna be a pain to redo it, just wanted to know if it worth it.


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## begreen (Jan 26, 2015)

What you have already done is an improvement for sure. It may be enough. Are you noting a difference in stove output? A metal block off plate will make a better barrier and will prevent insulation from falling out. You could make it out of two overlapping pieces of metal with a cut out in the middle so that you don't have to disconnect the liner. Here's a couple examples:
https://www.hearth.com/talk/threads/another-block-off-plate-install-with-pics.71281/
https://www.hearth.com/talk/threads/poor-mans-block-off-plate-ii.73018/


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## Dmitry (Jan 26, 2015)

It was brand new insert install and I can't compare heat output. Nothing to complain so far.
Thanks for the links. The poor man block off plate might work without removing the insert.


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## WoodpileOCD (Jan 26, 2015)

Don't know how much space you have above your insert. I went this route and it worked great but I don't think I could retrofit it now without pulling the insert. You might have more room though.


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## Excavator (Jan 26, 2015)

I cut out damper, chipped out some brick and installed 8 inch insulated liner. Then i fabbed up my own block off plate. 
i highly recommend using one if u can. the performance is great.


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## Copper44 (Jan 27, 2015)

This is what I modeled up for my Block-Off plate.


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## Copper44 (Jan 27, 2015)

Maybe putting them in directly will help some others as well.


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## mstoelton (Jan 27, 2015)

OP is the insert making heat?  Are you happy with the amount?  Generally Roxul is a poor substitute for a good block-off plate.  There are many less that satisfied owners who have installed or paid to have inserts installed and found this out.  Yes it is a pain to install.  Yes they work.  I spent a full day installing my 2nd block-off plate for my 2nd insert.  Yes, they can be difficult, and yes you can make a block-off plate in more than 1 piece.  Just overlap and seal it to the best of your abilities.

Note: a full face shield is helpful when installing these.  I actually got inside the fireplace upside down and used my legs to push the block-off plate into place.  Once in place, I used tapcons to hang it and then sealed the edges with silicone stove sealer.


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## Dmitry (Jan 31, 2015)

Where I can buy a sheet metal that I can fabricate into block off plate? Wondering if HD has it.


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## cableman (Jan 31, 2015)

Dmitry said:


> Where I can buy a sheet metal that I can fabricate into block off plate? Wondering if HD has it.



Yes hd has it. I used a sheet of aluminum from hd for a buddys install which he had picked up.


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## Dmitry (Jan 31, 2015)

I see online there is aluminum , zinc metal and galvanized steel options available .What is the best option?


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## cableman (Jan 31, 2015)

Steel handles higher heat then aluminum but if your melting the aluminum theres gonna be other things to worry about!


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## Dmitry (Jan 31, 2015)

I guess aluminum is easier to work with, so it might be the best choice.


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## Brian26 (Jan 31, 2015)

I will probably get criticized like crazy but here is my install. Liner is fully insulated. I used the leftover liner insulation with the foil facing down to make a block off plate. I stuffed as much roxul as I could above it. I suggest installing a proper block off plate but works great for me with my insert.


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## kennyp2339 (Jan 31, 2015)

Brian26 - that looks good, as long as it works, it doesn't have to be pretty,


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## samfatboy (Jan 31, 2015)

It turned relatively cold here in Southern New England this January, and I had been running my wood burner insert with just the liner with no insulation or block off for about 6 years.  Last year I did some insulation work around my windows and doors, so my house is a little tighter now.  When we hit a couple weeks of below freezing weather, with multiple dips into the zero range, it became very apparent that I had a huge heat loss going up my chimney.  When I would wake up on those sub zero mornings, and the stove had gone out, it was like someone had left a door open to my family room.  

Two weeks ago I went to Home Depot and bought the Roxul and sheet metal to do the lower insulation and block off.  I basically followed the instructions that are posted above, as well as on the block off forum.  Mine was not pretty, but it is functional.  my opening was only 28 x 7, and I did have to use a metal cut-off wheel to cut the damper frame out where the liner comes through (did that on original install). My damper frame is metal, and actually runs down the inside of the chimney box about 8 inches, so I simply drilled 8 holes and used steel deck screws to hold the sheet steel damper in place.  I would say the damper only added about 30 minutes to the total project.  Definitely, stuffing the Roxul was much harder to do.  For those whom are contemplating insulation and block-off, if you invest the time in doing the insulation, you may as well do the block off while you are at it. 

The difference is huge.  The temperature in the room actually went up 5 degrees once I had the install completed, before I could  even get the insert back in place.  Now when I get up in the mornings and the stove is cold, the room no longer feels like someone left the door open.  Last night I put my final load in around 9 pm and passed out (long week at work).  This morning I woke up at 5:30, it was 6 degrees outside with 15 mph wind, and the house thermostat read 68 degrees.  The last time I had a similar situation, the thermostat was more like 59 degrees.  My average load burn times  on super cold days have increased from 4.5 hours to 8 hours, and I need to use a lot less wood. 

Taking out the insert is a hassle, but I do it once a year for maintenance anyway, so insulation and block-off should be a no brainer.  Don't know why I waited so long.


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## MJCT (Jun 4, 2015)

I just put a regency Hampton hi300 insert in and am having a tough time getting it hot.

I can fire it wide open with a full load of bio bricks (10)and the IR temp barely reaches 350 at the front of the stove and it only lasts 4 hours with not that much heat output which tells me something is wrong. 

 It's a center masonry chimney with 30' of un-insulated liner to a capped top. The cast iron surround isn't all that tight to the fireplace brick and there was no block off plate installed when the 6" liner was ovalized to fit through the damper opening. There's also what looks like an air supply vent built into the fireplace low on one side, which I'm not sure is affecting anything. 

Am I losing all my heat up the damper into the clay flue even though the flue is capped at the top? I was wondering if the fact that I only have one air control (intake at the bottom of the stove) is causing me to lose too much heat from inside the stove itself b/c I have no way of controlling air going out the "stack". 

My next step was to stuff some Roxul around the liner at the damper to see if that's the problem. Should I just be putting in a block off plate anyway or should I test it out with just the Roxul first?


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## bholler (Jun 4, 2015)

By controlling the air going into the stove you are controlling the air going up the stack.  There are several problems i see first running the stove wide open will not give you the most heat at all for more heat you need to shut it down.  Second what is the outside temperature.  Higher outside temps will hurt draft and make it harder to get the stove up to temperature.  Having the liner smashed to go through the damper will also hurt draft.   You liner should also be insulated to meet code and maintain the ul listing of the liner.  And finally the blockoff plate will not affect how hot the stove gets really but it will increase the heat output into the room.


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## Highbeam (Jun 4, 2015)

Code does not require liner insulation unless the masonry chimney has failed.


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## bholler (Jun 4, 2015)

Highbeam said:


> Code does not require liner insulation unless the masonry chimney has failed.


Not true at all what code are you referring to?  Irc requires insulation unless you have the proper clearance not a word about the condition of the chimney


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## Highbeam (Jun 4, 2015)

bholler said:


> Not true at all what code are you referring to?  Irc requires insulation unless you have the proper clearance not a word about the condition of the chimney


We're probably saying the same thing. If your existing masonry chimney meets current code then your liner does not need to be insulated.


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## bholler (Jun 4, 2015)

Highbeam said:


> We're probably saying the same thing. If your existing masonry chimney meets current code then your liner does not need to be insulated.


true but in my experince very very few have the required clearance any it is next to impossible to verify if they do so i always assume they do not have that required clearance


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## Highbeam (Jun 5, 2015)

bholler said:


> true but in my experince very very few have the required clearance any it is next to impossible to verify if they do so i always assume they do not have that required clearance



So you have chosen to assume that no masonry chimney is safe or built properly. Many of our members here, perhaps the majority, use a regular masonry chimney for either their stoves or for some other appliance in their home.


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## kennyp2339 (Jun 5, 2015)

There is nothing wrong with using a masonry chimney for a wood stove ( not slammer type) as long as there are proper clearences from the masonry to combustible wall, some houses built in earlier times did not follow the clearences requirements. Durning a normal stove operation everything was fine but if there was an overfire or chimney fire, there would be extension leading to structure fire. Also masonry needs to be inspected as with all chimneys for cracks in the tile and degrading mortar joints. Even if you don't have a chimney fire, Inproper water drainage can also compromise the chimney.


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## begreen (Jun 5, 2015)

This is a tangent from the OP. If the masonry chimney's tile-lined throat is too large you should put in a liner to assure the cross-section is matched to the flue outlet. For this reason I would guess that the majority of inserts have chimney liners. Fireplace chimneys are usually too large to match the common 6" insert flue outlet size. I would guess that most of the members here follow that guidance.


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## bholler (Jun 5, 2015)

Highbeam said:


> So you have chosen to assume that no masonry chimney is safe or built properly. Many of our members here, perhaps the majority, use a regular masonry chimney for either their stoves or for some other appliance in their home.


No i am not saying they are not safe I work on many clay lined chimneys with wood stoves in them a few have proper clearance but most do not.  We tell the customer that they are not up to code but if they choose to use them anyway that is up to them and we will clean them.  But when i put a liner in it needs to be up to code and it is a pretty safe assumption that somewhere there is a combustible material to close to that chimney.  And regardless of the code issue liners work better when they are insulated.


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## Highbeam (Jun 5, 2015)

bholler said:


> liners work better when they are insulated.


 
For sure. Just don'tgo scaring folks into thinking that all liners must be insulated, that's just not true.


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## bholler (Jun 5, 2015)

Highbeam said:


> For sure. Just don'tgo scaring folks into thinking that all liners must be insulated, that's just not true.
> Blaze King Princess Ultra 2012


I am sorry but if you look at the ul listing they all do when installed for a wood burning appliance in order to maintain that listing.  Unless like i said they were tested with the proper clearances and no insulation which i have never seen.   And as far as how many don't need insulated because the chimneys have proper clearances i would say 1 or 2 out of 50 chimneys i inspect have that clearance.  I see many chimneys in new construction that don't have it.  The reason is that it is very difficult to build one with those clearances the whole way.   So i am sorry but in my opinion every single liner should be insulated and most need to be in order to meet code.   I am not trying to scare anyone i am just telling people what i have seen and learned in my years of experience and the many thousands of chimneys i have inspected and worked on.   And btw i never said all liners need to be insulated by code just most.


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