Block Off Plate - Insulation and My Chimney

[Bagelboy]

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

 

[tronsliver]

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.

 

[Bagelboy]

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.

 

[tronsliver]

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.

 

[iron]

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

 

[BrotherBart]

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.

 

[jatoxico]

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.

 

[jscs.moore]

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?????

 

[kennyp2339]

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.

 

[tinman100863]

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.

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

 

[SuperGenius]

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).

 

[tinman100863]

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!

 

[jscs.moore]

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!

 

[quotejso]

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

 

[jatoxico]

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.

 

[bholler]

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.

 

[Smoked]

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!

 

[kennyp2339]

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

 

[jatoxico]

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?

 

[kennyp2339]

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.

 

[jatoxico]

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.