# Block Off Plate - Insulation and My Chimney



## bryankloos (Jan 14, 2014)

Hey Guys,

I had an insert installed this November and I am loving it. 
That said, I am curious about insulation and the chimney.
The installer ran 6" stainless flue liner up my exterior masonry chimney which is about 20'.
The chimney is lined with 12"x8" flue tile and there was no insulation used during the installation as it was tight fitting the liner in the tile.  The installer had no intention to insulate regardless as he didn't know the sizing before coming to my property for the first time at the install.

Anyway, I'm wondering if it would be advantageous to install a block off plate and insulate the flue space.

At the end of the day the heat output is good and the draw is fine.

Thoughts?

Bryan


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## mellow (Jan 14, 2014)

100% yes to the block off plate, search on here how to do one.  If you are getting good draft and your flue tiles are not cracked then you should be ok with no insulation on the liner.


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## begreen (Jan 14, 2014)

Yes, with an exterior chimney, you will get more heat and use less wood . 

https://www.hearth.com/talk/wiki/why-damper-seal-is-needed/


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## tronsliver (Jan 15, 2014)

begreen said:


> Yes, with an exterior chimney, you will get more heat and use less wood .
> 
> https://www.hearth.com/talk/wiki/why-damper-seal-is-needed/


My installer who designs, builds, and repairs chimneys was adamant about not installing a blocking plate in a chimney with a clay flue.  He said once the top is capped off it is best to allow the heat to rise up from the removed damper to eliminate moisture.  Further, he stated that the heat also improves draft because the cavity does not cool the metal chimney pipe attached to the insert.  He also said you may get additional BTUs  by capping the damper but possibly pay a few thousand or more later when the chimney flue begins to crumble from excessive moisture.  He has been doing this line of work for 40 years and is well respected in the field.


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## PLAYS WITH FIRE (Jan 15, 2014)

That is interesting point.....I would think though with all the hundreds or thousands of years experience collectively on here someone would have had problems like this....I mean sewage pipes used to be made form Terra-cotta and I've seen them dug up after many decades in the ground in near perfect condition.....granted not exposed to heat like a flue. I've been to Europe and have seen roofs made from TC that's 1200+ years old in near perfect condition. I'd image those have been though many expansion/contraction cycles and are original....that's very interesting point and I'm not arguing!


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## mstoelton (Jan 15, 2014)

Where would the "excessive moisture" come from?  If there is a blocking plate in the flue and it is sealed at both ends (at the blocking plate and the cap) there should not be a way for any "excessive moisture" to get into the clay liner.  If there is a way for the moisture to get into the clay liner then there is most likely a way for it to get out!  And further, if you are installing a sealed top plate, would that not effectively prevent the rising heated moisture from escaping at the top?  I'm not an installer, mason, or a fireplace guru, but I do know my physics, and general engineering.    

Maybe the installer was giving you a line of horse apples so he didn't have to make a blocking plate for each of his installs!


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## Nick Mystic (Jan 15, 2014)

I think it would depend on what sort of chimney and stove/insert set up you have. In my case I have a 25' tall masonry chimney that is 4'x8' and contains over 6500 bricks. I have a 6" flex liner inside of an 11"x18" clay tile flue. When I changed out my old insert for a Jotul F 600 free standing stove I put in a metal block off plate with insulation above it. I also put insulation down my chimney about 4 - 5 feet around the liner to the roof line. Along with sealing off my top plate with silicone caulk. With this set up my chimney bricks around the top of the fireplace opening hit 250 F. Fifteen feet up the chimney is reading 95 F. I've got to believe a lot of heat is still getting to the clay tile liner driving out any moisture concern.


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## mstoelton (Jan 15, 2014)

On the subject of insulation, based on the reading I have done on this forum, insulation will help reduce the build-up of creosote in  your liner because it will help the  liner stay warm once heated by your fire.  Insulation will minimize the condensing of creosote in your liner that could be cold on the outside because you have an external chimney and you live in CT. 

You might have some limitations on how to insulate in the 8x12 clay liner.  You may need to do a poor in type insulation and that would almost necessitate the block-off plate.


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## tronsliver (Jan 15, 2014)

mstoelton said:


> Where would the "excessive moisture" come from?  If there is a blocking plate in the flue and it is sealed at both ends (at the blocking plate and the cap) there should not be a way for any "excessive moisture" to get into the clay liner.  If there is a way for the moisture to get into the clay liner then there is most likely a way for it to get out!  And further, if you are installing a sealed top plate, would that not effectively prevent the rising heated moisture from escaping at the top?  I'm not an installer, mason, or a fireplace guru, but I do know my physics, and general engineering.
> 
> Maybe the installer was giving you a line of horse apples so he didn't have to make a blocking plate for each of his installs!



The way it was explained if you cap the damper then the cold chimney (brick and flue) exposed to the hot metal chimney creates condensation. If the chimney can't breath (like an attic that has the soffits blocked) moisture collects.


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## tronsliver (Jan 15, 2014)

mstoelton said:


> Where would the "excessive moisture" come from?  If there is a blocking plate in the flue and it is sealed at both ends (at the blocking plate and the cap) there should not be a way for any "excessive moisture" to get into the clay liner.  If there is a way for the moisture to get into the clay liner then there is most likely a way for it to get out!  And further, if you are installing a sealed top plate, would that not effectively prevent the rising heated moisture from escaping at the top?  I'm not an installer, mason, or a fireplace guru, but I do know my physics, and general engineering.
> 
> Maybe the installer was giving you a line of horse apples so he didn't have to make a blocking plate for each of his installs!



Not that type of guy. He is well respected in the field and there is a waiting list to get his services. As I stated in my original post he designs, builds, and repairs chimneys. He has a website Fennerbuilders.com


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## tronsliver (Jan 15, 2014)

PLAYS WITH FIRE said:


> That is interesting point.....I would think though with all the hundreds or thousands of years experience collectively on here someone would have had problems like this....I mean sewage pipes used to be made form Terra-cotta and I've seen them dug up after many decades in the ground in near perfect condition.....granted not exposed to heat like a flue. I've been to Europe and have seen roofs made from TC that's 1200+ years old in near perfect condition. I'd image those have been though many expansion/contraction cycles and are original....that's very interesting point and I'm not arguing!


I understand your comments. I too had a hard time wrapping my mind around this.  But the more I thought about it the more sense it made.  Once the cavity is heated or put another way - approaches equilibrium with the temperature of the stove then the stove will significantly reduce giving away BTUs to the cavity.  The benefit is a hot cavity which starves off moisture and a hot temperature surrounding the chimney pipe keeping the smoke hot as it exits the chimney.  This increases draft and allows the smoke to rise more efficiently.  Cold smoke sinks like a hot air balloon when heat is removed.


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## mstoelton (Jan 15, 2014)

Tronsilver

I understand your thinking with respect to the cold flue collecting condensation, however, this would only happen if there were air (containing water vapor) circulating in a chimney outside of the liner.  If the circulation is stopped (sealed at top plate and at the flue blocking plate), then there is no opportunity to collect condensation.  Water vapor is not going to come from the chimney liner and the top and bottom plate are sealed so were does the condensation come from - answer - it doesn't.  The scenario you describe only happens if you don't have a flue blocking plate in place!  If water vapor travels through the chimney walls - then it can exit the same way.

The attic scenario does not compare because you cannot have a sealed attic- there are always sources of airflow, and sources of humid air in an attic. 

Without an air source (open flue plate) condensation can't happen in a chimney because there is not a source for water vapor if it is sealed at top and bottom.  Condensation just doesn't happen - condensation is carried by circulating air.

On the other hand if you do not install a flue block, then humid air will cause a collection of condensation to collect in your chimney due to the air circulation from your living space entering the area between your liner and your chimney tile,  and yes then you will have condensation in your chimney.  with a blocking plate in place and sealed, this should be eliminated.

Note: I am talking about a blocking plate made of  galvanized steel  that is sealed between the appliance and the  flue  plate.  It can be made airtight.


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## elmoleaf (Jan 16, 2014)

Brick and mortar are not impermeable. Rain soaked brick can absorb water and release vapor to the interior. Google effluourescence for examples. 
The potential depends on installation specifics like exposure, if you have an adjacent flue and it's separation, presence  and condition of clay liner, etc.


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## Bagelboy (Jan 16, 2014)

I could be wrong, but  I would also think rain soaked brick will absorb water. I also have a 30 foot brick exterior wall chimney. There could very well be cracks as you get higher up the chimney in some of the mortar. Would this allow moisture to enter? I don't know but is sounds like it would. So, with the block off plate installed at the top of my chimney by my installers, and than the cap put on, would I be doing myself harm installing a plate on the inside bottom as well?


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## mstoelton (Jan 16, 2014)

If the brick/mortar/flue liner allow water to enter due to cracks or just due to not being impermiable then they would also allow the water to exit in the same manner.  The flue block will not stop the water from moving out in the same manner in entered. 

It will reduce the amount of heat lost to the chimney.


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## tronsliver (Jan 16, 2014)

Bagelboy said:


> I could be wrong, but  I would also think rain soaked brick will absorb water. I also have a 30 foot brick exterior wall chimney. There could very well be cracks as you get higher up the chimney in some of the mortar. Would this allow moisture to enter? I don't know but is sounds like it would. So, with the block off plate installed at the top of my chimney by my installers, and than the cap put on, would I be doing myself harm installing a plate on the inside bottom as well?


I had the same doubts especially after reading numerous posts about the benefits of a blocking plate. And believe me I quizzed my installer on this topic because I was convinced I was right.  He also stated that during his 40 years of working with chimneys the UL standards had changed numerous times and there is no longer a requirement for damper blocking plates because of the moisture issue.  I suppose some insert manufacturers want you to have as much thermal efficiency as possible and are not concerned about damage that may take a number of years to show it's ugly face  ( crumbling flue from moisture) so a damper blocking plate is recommended in their installation instructions.  I was further convinced when I searched google for "chimney sweeps" and read info on their sites staring the number one enemy of masonry chimneys is moisture.  So for me I'd rather error on the side of caution and listen to a guy with 40 years of experience running a successful business who has personally inspected a thousand chimneys and seen the damage firsthand.  I completely understand that each person contemplating this issue will need to make a personal choice based on their own reasoning because there is nothing available that specifically states "don't install a damper blocking plate for these reasons."  This topic reminds me of the argument about cigarette smoking, I'm sure you too heard the person espousing the reason for not quitting : " my grandfather smoked for 40 years and lived to be 80."


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## mellow (Jan 16, 2014)

Meh, if the terracotta goes after 20 years I will just bust it out and it will give me an excuse to install rigid insulated pipe, of course who knows if we will still be able to burn in 20 years.


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## tronsliver (Jan 16, 2014)

mellow said:


> Meh, if the terracotta goes after 20 years I will just bust it out and it will give me an excuse to install rigid insulated pipe, of course who knows if we will still be able to burn in 20 years.


I hear ya. In my instance the chimney is already 35 years old so I want to help the old girl make it a while longer. Don't want to spend another 3 - 5K on top of the 5k I just spent for the installed insert.


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## mellow (Jan 16, 2014)

Mine was built in 1955, the terrcotta flue has cracks in it but the chimney overall is still structurally sound and should be good to go for another 50 years,  just saying if the terracotta goes it isn't a deal breaker due to the block off plate.

I for one would rather have those BTU's going to my living space.


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## tronsliver (Jan 16, 2014)

I thought I'd share the email my installer sent me concerning the damper blocking plate. Not trying to change anyone's mind just injecting information for consideration. As implied in the email I was pretty firm on my original opinion and as such he finally says OK if you're not going to listen to me then at least forgo the metal plate and just use insulation. He does though throw in the caveat that I still may be playing with fire (no pun). I also found interesting the part about UL and warranty.  


"There are more factors than what you are considering, I have been a mason and fireplace installer for over forty years, I can tell you that most old sites on insert installations show a blocking plate, but those with a blocking plate don't have a seal at the top of the chimney. Blocking plates were required years ago when liners were not required, the clay flue liners have to breathe or they will deteriorate from moisture and sweat.

Especially when you have an outside chimney. Cold chimneys create poor performance and a cold chimney with a warm liner in it  will not only cause the liner to sweat but also the empty spaces between the liner and the brick exterior. I have seen this many times. The chimney will crumble.  Blocking plates also make the installation, cleaning and maintenance very difficult because the liner can't move inside the firebox, the only thing I would recommend in place of the blocking plate would be fiberglass insulation in the damper, which the manufacturer  suggests as an alternative but even then, you trying to increase output, may wind up shooting yourself in the foot with future chimney repair that can be many thousands of dollars. I have seen many laws and codes come and go over the years because of  their failures, the biggest problem with homes today is that they are made too tight and causing environmental hazards and home damage. At least with the insulation some moisture can wick out. I fix hundreds of fireplaces each year from one to two hundred years old and can tell you the history of each success and failure in design.  These plates are not available with any ul listing any more and any item installed affecting the operation of the UL listing of the stove will void the warranty. I strongly recommend allowing the chimney to warm up with the fire."


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## mellow (Jan 16, 2014)

I understand what he is saying now.  You used to be able to run the liner to the first tile with a damper plate installed. I guess you could have run it without a chimney cap and I can see his point with no cap.

But I do not see his point with a full liner to the top of the chimney and a top plate covering the chimney.


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## Bagelboy (Jan 16, 2014)

Well that's what I had installed. They installed my insert with a liner going all the way to the top of my 30' exterior brick chimney. They put a blockoff plate at the top and of course a cap. So, if moisture gets in the chimney from cracked mortar or from the bricks, will it also cause moisture problems since the moisture has nowhere to go? Another words, with the blockoff and cap, it can't exit. And, if this is the case, would installing another blockoff plate near the damper not only keep the heat inside my insert, but also have no affect on moisture since it can't go anywhere with the blockoff plate up at the cap?


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## hamsey (Jan 16, 2014)

Going back and forth about my install in a couple of weeks. Interior chimney 15 foot with another 9 foot outside with a 8x8 terracotta flue. I am currently making a block plate and the insert installer will install for me. Usually they just do rock wool but will do it for extra $. Putting in a Jotul C550. After reading the C550 thread I am worried that my space will be too warm. We keep the house around 61-63. When I build my fires I can get it up to the high sixties maybe 70 but that is feeding constantly feeding the fire. My first plate I had 8" above the insert. I found a new location with it about 18" above. I have some time so I will be watching this thread. 

Made a costly mistake about not putting in a big enough gas fireplace upstairs and do not want to make it again with the Jotul not heating the space. Keep on going back and forth. Better safe than sorry?


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## tronsliver (Jan 16, 2014)

Bagelboy said:


> Well that's what I had installed. They installed my insert with a liner going all the way to the top of my 30' exterior brick chimney. They put a blockoff plate at the top and of course a cap. So, if moisture gets in the chimney from cracked mortar or from the bricks, will it also cause moisture problems since the moisture has nowhere to go? Another words, with the blockoff and cap, it can't exit. And, if this is the case, would installing another blockoff plate near the damper not only keep the heat inside my insert, but also have no affect on moisture since it can't go anywhere with the blockoff plate up at the cap?


What he's saying is the top cap needs to be installed to keep out weather but no bottom plate so the chimney cavity can stay warm and breath. Choking it off by using a damper blocking plate allows moisture to accumulate.


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## tronsliver (Jan 16, 2014)

Bagelboy said:


> Well that's what I had installed. They installed my insert with a liner going all the way to the top of my 30' exterior brick chimney. They put a blockoff plate at the top and of course a cap. So, if moisture gets in the chimney from cracked mortar or from the bricks, will it also cause moisture problems since the moisture has nowhere to go? Another words, with the blockoff and cap, it can't exit. And, if this is the case, would installing another blockoff plate near the damper not only keep the heat inside my insert, but also have no affect on moisture since it can't go anywhere with the blockoff plate up at the cap?


The way I understand this is if the metal liner going up through the flue is warmer than the clay flue as a result of the ambient temperature then condensation can form.  It doesn't matter if the flue is cracked or not because the brick, flue, mortar are permeable. Think about a cement floor in some basements where moisture will form at times on the surface because of the differences in ground temperature compared to the heat of your home. This is basically the same physics.  By leaving the bottom of the chimney cavity open the heat from the stove will heat the cavity and keep the flue and chimney above the temperature needed for condensation to form. As stated in an earlier post moisture is the enemy of clay flues.


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## Bagelboy (Jan 17, 2014)

So, tronsliver, no plate on the bottom, while probably giving up btu's, heats the chimney to keep moisture from deteriorating your chimney, correct?


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## tronsliver (Jan 17, 2014)

Bagelboy said:


> So, tronsliver, no plate on the bottom, while probably giving up btu's, heats the chimney to keep moisture from deteriorating your chimney, correct?


Yes that's correct.


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## Bagelboy (Jan 17, 2014)

My chimney is now 25 years old, and at the same time I'd like to keep more of the btu's in the stove. Guess I'll have to think long and hard on a blockoff plate, although with this information, I tend to say I'll give up the btu's and not install the plate.


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## tronsliver (Jan 17, 2014)

Bagelboy said:


> My chimney is now 25 years old, and at the same time I'd like to keep more of the btu's in the stove. Guess I'll have to think long and hard on a blockoff plate, although with this information, I tend to say I'll give up the btu's and not install the plate.


 For me it's always been about thermal efficiency and low particulate matter so it made this choice difficult.  I arrived at my decision by thinking about the physics and then associating some of my life's experiences with attics and basement cement floors.  I don't think its necessary to repeat again what's already been posted in this thread but this just makes sense to me.  But again this is a personal choice because there is nothing that specifically makes the decision for you.  More importantly for me, is succumbing to the knowledge of a very successful mason with 40 years of experience working with chimneys.


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## iron (Dec 27, 2015)

thanks for this thread. very interesting counterpoints to the typical pro-blockoff plate threads.


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## BrotherBart (Dec 27, 2015)

Yeah, like condensation is going to stay in a chimney with a 600 degree liner in it. Block off plate or no block off plate. That top plate on the chimney ain't hermetically sealed lately.


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## jatoxico (Dec 27, 2015)

BrotherBart said:


> Yeah, like condensation is going to stay in a chimney with a 600 degree liner in it. Block off plate or no block off plate. That top plate on the chimney ain't hermetically sealed lately.



I agree. The block-off plate and top seal are not so tight that water vapor can't get out. In fact when I first fired up my new insert several years ago, steam started escaping outside all along the length of the chimney right through the brick and mortar joints. Freaked me out since I thought it was smoke. Posted here as a nervous as heck newb and spent several hours in the attic and on an extension ladder checking and re-checking. This was pre-plate.

Apparently what happened was after years of the chimney being idle and with the much higher flue temps from using a wood burning appliance, there was a good bit of water in the structure that steamed off. It has never happened again even after each years first fire or after adding a plate a couple years later. My conclusion the plate is not trapping water and any water is able to escape through the masonry. Good reason not to water seal though.


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## jscs.moore (Dec 27, 2015)

tronsliver said:


> I had the same doubts especially after reading numerous posts about the benefits of a blocking plate. And believe me I quizzed my installer on this topic because I was convinced I was right.  He also stated that during his 40 years of working with chimneys the UL standards had changed numerous times and there is no longer a requirement for damper blocking plates because of the moisture issue.  I suppose some insert manufacturers want you to have as much thermal efficiency as possible and are not concerned about damage that may take a number of years to show it's ugly face  ( crumbling flue from moisture) so a damper blocking plate is recommended in their installation instructions.  I was further convinced when I searched google for "chimney sweeps" and read info on their sites staring the number one enemy of masonry chimneys is moisture.  So for me I'd rather error on the side of caution and listen to a guy with 40 years of experience running a successful business who has personally inspected a thousand chimneys and seen the damage firsthand.  I completely understand that each person contemplating this issue will need to make a personal choice based on their own reasoning because there is nothing available that specifically states "don't install a damper blocking plate for these reasons."  This topic reminds me of the argument about cigarette smoking, I'm sure you too heard the person espousing the reason for not quitting : " my grandfather smoked for 40 years and lived to be 80."


You make some interesting points...I'm a newbie to all of this myself (had my insert installed in September 2015). I had a Hampton HI300 installed and based on webbing this site to death I insisted on a insulated liner (I have existing terracotta clay liner). The dealer said it wasn't necessary, but I insisted and got them to install a 6" ovalized SS, pre-insulated liner...my chimney is about 28ft high. I brought up installing a block off plate with them 2 or 3 times and was dismissed out right and was basically told it was NOT necessary. I know they sealed the top of the chimney cap with mortar after they completed the liner install so I guess that was good. However, the whole issue of the block off plate was very frustrating, the dealer essentially slap me down saying "we are the highest volume Regency dealer on the east coast and our techs go down the Regency factory on a regular basis for install workshops/trainings, etc...no one at Regency recommends block off plates as part of the installation for their inserts!" So as a newbie...the whole block off plate issue is very confusing. I have nothing to compare to, but my insert seems to draw really well and so far is kicking out a lot of heat (I know it hasn't been real cold so far this year). I think it just sucks that there is so much conflicting info on the subject of block off plates for inserts! It seems every poster on hearth.com says get one installed...but why don't the dealers say you should install one. P.S. It wasn't just the Regency dealer, when I was researching my purchase I consider a Quadrafire Grand Voyageur and that dealer also told me a block off plate was not needed or necessary?? Again, I just wish the industry had minimum standards that all dealers had to adhere to when it comes to installation. If research shows a block off plate will improve performance and provide more heat to your home...why the hell don't the dealers make it a routine part of their installation practice?????


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## kennyp2339 (Dec 27, 2015)

I'm installing a block off plate today at my parents house, There current setup is insert, non insulated 6" liner up 25ft to cap. When the insert was installed 10years ago, the installer said a block off plate was not needed because the cap of the chimney was covered and the flue would be kept warm.
After going back and forth a couple years, my dad is finally on board with installing the plate, the idea is let the stove heat the room, the non insulated liner will raise the temp of the chimney (flue temps 450 - 600)
Worst case scenario would be that condensation forms, it drips out, or the liner becomes plugged up quicker and we realize the block off plate was detrimental and we take the thing out, we are willing to take that chance.


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## tinman100863 (Dec 27, 2015)

mstoelton said:


> Tronsilver
> 
> I understand your thinking with respect to the cold flue collecting condensation, however, this would only happen if there were air (containing water vapor) circulating in a chimney outside of the liner.  If the circulation is stopped (sealed at top plate and at the flue blocking plate), then there is no opportunity to collect condensation.  Water vapor is not going to come from the chimney liner and the top and bottom plate are sealed so were does the condensation come from - answer - it doesn't.  The scenario you describe only happens if you don't have a flue blocking plate in place!  If water vapor travels through the chimney walls - then it can exit the same way.
> 
> ...


moisture is entering thru the bricks and mortar , yes coming in, and not all of it is always exiting out !


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## SuperGenius (Dec 27, 2015)

kennyp2339 said:


> I'm installing a block off plate today at my parents house, There current setup is insert, non insulated 6" liner up 25ft to cap. When the insert was installed 10years ago, the installer said a block off plate was not needed because the cap of the chimney was covered and the flue would be kept warm.
> After going back and forth a couple years, my dad is finally on board with installing the plate, the idea is let the stove heat the room, the non insulated liner will raise the temp of the chimney (flue temps 450 - 600)
> Worst case scenario would be that condensation forms, it drips out, or the liner becomes plugged up quicker and we realize the block off plate was detrimental and we take the thing out, we are willing to take that chance.



Please update us afterward. Curious to see if it makes a noticeable difference in performance at least (maybe post again in 40 or 50 years if you notice any chimney crumbling).


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## tinman100863 (Dec 27, 2015)

jscs.moore said:


> You make some interesting points...I'm a newbie to all of this myself (had my insert installed in September 2015). I had a Hampton HI300 installed and based on webbing this site to death I insisted on a insulated liner (I have existing terracotta clay liner). The dealer said it wasn't necessary, but I insisted and got them to install a 6" ovalized SS, pre-insulated liner...my chimney is about 28ft high. I brought up installing a block off plate with them 2 or 3 times and was dismissed out right and was basically told it was NOT necessary. I know they sealed the top of the chimney cap with mortar after they completed the liner install so I guess that was good. However, the whole issue of the block off plate was very frustrating, the dealer essentially slap me down saying "we are the highest volume Regency dealer on the east coast and our techs go down the Regency factory on a regular basis for install workshops/trainings, etc...no one at Regency recommends block off plates as part of the installation for their inserts!" So as a newbie...the whole block off plate issue is very confusing. I have nothing to compare to, but my insert seems to draw really well and so far is kicking out a lot of heat (I know it hasn't been real cold so far this year). I think it just sucks that there is so much conflicting info on the subject of block off plates for inserts! It seems every poster on hearth.com says get one installed...but why don't the dealers say you
> should install one. P.S. It wasn't just the Regency dealer, when I was researching my purchase I consider a Quadrafire Grand Voyageur and that dealer also told me a block off plate was not needed or necessary?? Again, I just wish the industry had minimum standards that all dealers had to adhere to when it comes to installation. If research shows a block off plate will improve performance and provide more heat to your home...why the hell don't the dealers make it a routine part of their installation practice?????


my conclusion is this .The Manufactures & dealers are not looking for a short cut , They are going by feed back from previous issues.  I myself was also worried about my installer putting in only a top plate ,but it makes sense to me. hey if a person wants a block off at the damper ,then get it done and deal with the problem later if it rises!


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## jscs.moore (Dec 27, 2015)

tinman100863 said:


> my conclusion is this .The Manufactures & dealers are not looking for a short cut , They are going by feed back from previous issues.  I myself was also worried about my installer putting in only a top plate ,but it makes sense to me. hey if a person wants a block off at the damper ,then get it done and deal with the problem later if it rises!


Yeah...wish I knew the answer to why the dealers seem so opposed to the block off plate? Not sure if it isn't just short cutting the job because it obviously requires more time and work...and if your doing 3 installs a day this time of year (that's what the dealer techs told me their volume was the day of my install)...then I guess block off plates are just a pain in the ass to them? I will probably give it some time to really get a sense of how my insert performs over time...but if I do go with a block off plate, I would be very reluctant to ask the dealer to install given they were so dismissive of them in the first place! Like I said...just wish if there is so much to be gained by having a block off plate on installed with an insert, it would just be an industry standard and never questioned. The whole topic is very, very frustrating for us newbies!


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## quotejso (Dec 27, 2015)

Bagelboy said:


> So, tronsliver, no plate on the bottom, while probably giving up btu's, heats the chimney to keep moisture from deteriorating your chimney, correct?


What ABOUT the heat just off the pipe is tgat not enough cmon man


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## jatoxico (Dec 27, 2015)

tinman100863 said:


> moisture is entering thru the bricks and mortar , yes coming in, and not all of it is always exiting out !


The air space between the exterior surface of the tile lining and the brick is already sealed top and bottom when a chimney is constructed so there is no air flow on that side at the outset. So the idea is the exterior surface of the clay tile can be sealed but not the interior surface? Makes no sense to me.


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## bholler (Dec 27, 2015)

Ok we design build repair and maintain chimneys also and i have never seen or heard any real evidence to support this claim of damage caused by sealing top and bottom of the chimney.  I have seen moisture problems on the other hand by sealing the top and not the bottom.  This allows moist air in it condenses and then you have water.  I have been doing this a long time and have put in hundreds of block off plates with no issues caused by them yet.


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## Smoked (Dec 27, 2015)

Trying to wrap my head around this one.  I have to think the flue itself (even if insulated) is going to add far more heat to that space than convection off of the stove, especially higher up...unless you intentionally vent the space from the top.  Keep in mind, this is a pretty small gap between the liner and clay in most cases so it is really not going to take long to get it nice and toasty.  I don't think we are saving tuns of direct heat by using block-off plates, but i think we are making our homes more efficient or less drafty.  I also think most chimneys are going to have some leakage (air) so there will be some drying even with a perfectly sealed block-off plate.  I know neither of mine are perfect so I am not sweating it too much

Some things that might make a difference:
Clay liner or not?  A much larger area to heat to get beyond any potential condensation.
Continuous burner vs. occasional.  Continuous burners (maybe fewer this year) are going to heat that space one way or another.
Insulated liner vs not.  Draft is not gong to be altered much by block-off plate or not if you have an insulated liner.
Tightness of the chimney structure.  Is it self ventilating anyway? 
Climate.  is the structure going to dry from the outside in anyway?

I kind of think if you are really worried about fresh air into the old flue space, the right thing to do is vent the top plate and vent the smoke chamber just above the block-off so you are not wasting heated room air for this purpose.  If this was a legit need, I would think someone smarter than me would be recommending it to the masses.  

70 something here today but maybe a wedge will get it cool enough tomorrow to get something burnin.  Cheers!


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## kennyp2339 (Dec 27, 2015)

SuperGenius said:


> Please update us afterward. Curious to see if it makes a noticeable difference in performance at least (maybe post again in 40 or 50 years if you notice any chimney crumbling).


The block off plate is a fail for now, we could not get the liner off the flue collar at the insert level, in order to get the insert free we would have had to setup a ladder and climb the chimney about 35ft off the ground (grade is 10ft below fireplace, chimney is about 25ft) and disconnect the liner at the top and lift it off, I personally didn't feel like working that high in a mist rain day, My dad and I will try this again in the spring when its nice out


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## jatoxico (Dec 27, 2015)

kennyp2339 said:


> The block off plate is a fail for now, we could not get the liner off the flue collar at the insert level,


Bummer. No room to add it in two pieces either I guess? How about just stuffing with Roxul temporarily?


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## kennyp2339 (Dec 27, 2015)

jatoxico said:


> Bummer. No room to add it in two pieces either I guess? How about just stuffing with Roxul temporarily?


The fireplace is a true brick and mortar unit, the builders also put a heatilator in, when we replaced the heatilator we simply cut out portions of it so the insert would fit the envelope, unfortunately the top of the old heatilator is so close to the top of the insert that the only way to fit anything between the two (like a hand) is to pull the insert out completely. We'll get her done in the spring once the weather warms up.


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## jatoxico (Dec 27, 2015)

kennyp2339 said:


> unfortunately the top of the old heatilator is so close to the top of the insert that the only way to fit anything between the two (like a hand) is to pull the insert out completely.


Mine's that way too, can barely squeeze a hand in.


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