To Block Off Plate or Not To Block Off Plate

[jadm]

Another quandry

I have read about block off plates here on the site as I was referred to earlier and I have been calling around our area asking for information in regards to a block off plate at the damper area.

Two reasons have come up. One is that it keeps heat down in the insert area instead of going up the chimney and being lost heating the bricks there. My chimney is internal so the heat loss isn't as dramatic as it would be in an external chimney.

The other reason is a safety concern in that if there were a fire the block off plate would keep the flames from going up into the chimney and possibly going through any cracks in the masonry and catching attic materials on fire and thus a house fire..

If an insert has a ss liner, as mine does and it extends all the way up my chimney and out the top, how would the fire get out of it into the chimney proper?? My understanding is that a chimney fire, if it were to happen, in an insert with a liner would be contained in the liner and wouldn't get into the masonry part of the chimney at all.

I am getting conflicting info. in regards to if one is necessary with a full liner. I do have one at the top of my chimney which is where most people say one is a necessity.

It just seems to me that one isn't as necessary with an internal chimney and a fully lined insert.

So I'm back to the forum for more personal input from those of you who have had experience with a lower block off plate as well as having not had one previously. What have you found in having it both ways?

My installer came yesterday to inspect chimney and fireplace and said all looks ok for install of the Jotul 550. I asked him about the lower plate and he said it wasn't necessary due to how my set up is.... He is a full time fireman as well as an installer.....I'm befuddled so I figure just what I need is more info!

 

[Hogwildz]

Another quandry

I have read about block off plates here on the site as I was referred to earlier and I have been calling around our area asking for information in regards to a block off plate at the damper area.

Two reasons have come up. One is that it keeps heat down in the insert area instead of going up the chimney and being lost heating the bricks there. My chimney is internal so the heat loss isn't as dramatic as it would be in an external chimney.
IN your case not so bad.

The other reason is a safety concern in that if there were a fire the block off plate would keep the flames from going up into the chimney and possibly going through any cracks in the masonry and catching attic materials on fire and thus a house fire..
I think your understanding that backwards. If you have a chimney fire, and say the liner takes heat long enough to fail. The block off plate will also keep the flames from drafting back into the house through the damper area. Its a safety measure that is a no brainer for me. You can justify needing one, or not needing one. End result, with it, its another degree of safety and can hurt at all. Any extra safety measures is always a plus in my book.


If an insert has a ss liner, as mine does and it extends all the way up my chimney and out the top, how would the fire get out of it into the chimney proper?? My understanding is that a chimney fire, if it were to happen, in an insert with a liner would be contained in the liner and wouldn't get into the masonry part of the chimney at all.

I am getting conflicting info. in regards to if one is necessary with a full liner. I do have one at the top of my chimney which is where most people say one is a necessity.

It just seems to me that one isn't as necessary with an internal chimney and a fully lined insert.

So I'm back to the forum for more personal input from those of you who have had experience with a lower block off plate as well as having not had one previously. What have you found in having it both ways?

My installer came yesterday to inspect chimney and fireplace and said all looks ok for install of the Jotul 550. I asked him about the lower plate and he said it wasn't necessary due to how my set up is.... He is a full time fireman as well as an installer.....I'm befuddled so I figure just what I need is more info!
Ask the installer/fireman why would he advise against an added safety measure. He won't tell you that a block off plate is a PITA to install, and he won't make enough off it for the hassle. Ask him if the liner does take over 2100 degrees from a chimney fire for longer than testing standards, and the liner does for whatever reason fail............... what will stop the fire from back drafting back into the house at bottom without block off plate?
Bottom line, is if you can sleep ok at night, with you wife/kids/ yourself, and not worry, then don't sweat it and leave it off.
Personally, if a fireman or anyone for that matter came to install my insert, and told me I didn't need an extra added benefit of protection, I don't think I would be as comfortable with them installing my insert.
Per the manual if the liner is run all the way up, a block off plate is not required. (Only a direct connect requires per manual. But a go back to an extra added safety measure. Up to you.
Good luck with the install, and send pics

 

[elmoleaf]

The bottom block-off plate (or rockwool insulation at same location) will prevent the space around the ss liner from acting as a second chimney (allowing warm air to rise up & out of the living spaces) if the top plate at the exterior isn't well sealed or insulated.
This will also keep that same airspace warmer, which will allow the chimney to draft better.

However, if the top plate is well sealed and/or insulated, I'm not sure if you'd notice much difference by adding the bottom blockoff/insulation. The bottom blockoff is a small measure of added safety if the ss liner fails...in theory, it'd cut off any additional oxygen feeding a fire up in the chimney and prevent burning debris from falling down & out into the living space.

 

[swestall]

Making it really simple, everything said above and

YES, a blockoff plate is needed, yes it IS needed: because it provides a saftey barrier and keeps the heat in the house.

 

[nshif]

Another point is that some of your chimney is in the attic and some is outside above the roof. Heat rises and these areas are going to suck heat the could have gone to heating your house instead of the attic or great outdoors.

 

[North of 60]

Fire up that insert outside before you install it. Get her cooking like ya would on a cold day. Use your bare hands and place it all around the top and back
of the insert when shes been up to temp for a while. Now decide if you want to waste that heat into your masonary or not. Interior or not. Take in the other added saftey factor, the extra effort it takes to install it seems like it would be worth the gamble. By the way shes not a gamble. I can remember times that I would take more effort to find a reason not to do something than to actually just do it! There is enough pros and cons on this site to leave you with no question but to do it with a little bit of extra work. Good luck and cheers.

 

[jadm]

Okay - I get it. I am a knitter and not a builder so this all gets me pretty overwhelmed. I read the 'how to' article but I have to ask more questions because I can't comprehend something unless I actually physically do it. ( The only way I can explain this is that when I read a pattern to knit something it makes absolutely no sense to me. When I simply begin knitting one stitch at a time the directions begin to make sense and after I have completed whatever I am knitting I can then read the pattern and it makes sense to me.....it's a brain thing...)

Anyway, since I am not going to be making this myself I need to clarify where I measure. My installer has never done one of these things either so I need to be accurate. I don't think he minds the extra work as he will charge me for it which I don't mind paying because he is very reasonable and doesn't try to rip people off. Just a good person in general.

Do I measure below my damper area even though he will have to remove more of the damper apparatus in order for my ss liner to have a straighter shot to the top of the unit? (First installer didn't remove enough so when liner was pulled through he formed it into a bit of an oval shape so he could pull it through....not a good idea.)

When I have that measurement how do I determine where to have them cut a hole for the liner? It seems like it would be easier to have an extra piece with an indentation that can be added and fit snuggly around the ss liner if I get it cut in a collar type of cut.

What brand/type of insulation is rcmd. to be placed on top?

Sealants...I know many will not take the extreme heat of a wood burning flue and will simply get brittle and crumble out after a few fires. I have had that experience 3 times now with my current insert. It was originally sealed with a sealant that flaked off. Another person came out and said it had been the wrong type of sealant meant for gas fireplaces and said he had appropriate sealant for wood burners. He applied it.....It did the same thing. A few months ago I had a 3rd person come out (All independent chimney people. All with the right certifications/qualifications req. by the state) and he said last sealant not the right stuff and he applied sealant again that was recommended for these high heats.....It met a similar fate....

So you can see I am a bit leary of sealants. If any of you have successfully used a sealant and it is still intact please be specific with the brand name! People have rcmd chimney cement but I have no clue what that is. Can I purchase the sealant myself or is it something a licensed worker can only get??

I do agree with all of you in taking the extra measure so my hesitancy isn't in cutting costs. It's about trying to reduce my feelings of being overwhelmed with this project.


Just re read the 'how to' pages and I headed out the door to a neighbor's house who is a builder and I am sure he will be able to make sense of it. I do see that that despite what I have done to the damper area the measurement is down by the lintel area so what has been done above it doesn't matter...Am I right with that assumption?

Hopefully he can do this because my brain is close to panic!

 

[jtp10181]

In most cases with a full liner a block off plate is NOT required. This is not to say its not a good idea to have one, but it is not required by the manufacturers or by any national code.

 

[begreen]

I just noticed in the C550 manual that Jotul has clarified it's block-off plate requirement as compared to the older insert manuals. This makes more sense.

3. A sealed block-off plate must be installed at the damper area of the existing fireplace, unless the liner is connected to the top of the chimney.

 

[swestall]

The installer can make a cardboard template of the plate and have a sheet metal man make it for them. Can someone else chime in with a link to order one off the net?

 

[jadm]

Swestall - I think I am okay now. I took the article from this web site on how to build a block off plate to a neighbor who is also a builder and I also took the photos of iceman's install. He had no problem understanding what I need and will come over tomorrow to take the needed measurements for me. I will take the drawings to a sheet metal shop nearby and have them make the plate. My neighbor can't make it because he has no way to bend the metal for the flanges cleanly.

I'm calling my installer tomorrow to let him know I'm going with this plate. I can't imagine he will have a problem with it since I'm supplying all that is needed. It does seem pretty simple to install especially since the area will all be cleaned out.

What type of insulation should I get to put on top of it? How many inches deep?

What gauge sheet metal should I request?

How important is the cement around the liner and the plate? ( As you may have read I have had miserable luck with any of that stuff holding up to flue temps.) The plate he is designing will fit very snugly around the ss liner so the amount of air getting through it seems pretty minimal to me.

All of you thanks for your input!! It is greatly appreciated

 

[swestall]

You could use the same wool blanket type insulation and metal tape to secure it to the plate. If you use a bead of stove cement (get the kind that comes in the caulking gun tube) all around the plate and pull it down a bit for a good seal.
Run a bead around the place where the liner goes through also.

 

[jadm]

Sounds easy enough! What gauge metal should the plate be made of?

You could use the same wool blanket type insulation and metal tape to secure it to the plate. If you use a bead of stove cement (get the kind that comes in the caulking gun tube) all around the plate and pull it down a bit for a good seal.
Run a bead around the place where the liner goes through also.

 

[jadm]

Picture may follow install providing I can get my teenage son or husband to help me figure out how to do the picture thing on this site. I don't dare try to figure it out yet as all this install stuff has my brain on overload and any new info. is sure to begin popping my old circuits. I break out in a cold sweat just thinking about reading any more directions about anything right now!

Install won't happen for a few weeks as my installer is going on vacation at the end of this week.

Another quandry

I have read about block off plates here on the site as I was referred to earlier and I have been calling around our area asking for information in regards to a block off plate at the damper area.

Two reasons have come up. One is that it keeps heat down in the insert area instead of going up the chimney and being lost heating the bricks there. My chimney is internal so the heat loss isn't as dramatic as it would be in an external chimney.
IN your case not so bad.

The other reason is a safety concern in that if there were a fire the block off plate would keep the flames from going up into the chimney and possibly going through any cracks in the masonry and catching attic materials on fire and thus a house fire..
I think your understanding that backwards. If you have a chimney fire, and say the liner takes heat long enough to fail. The block off plate will also keep the flames from drafting back into the house through the damper area. Its a safety measure that is a no brainer for me. You can justify needing one, or not needing one. End result, with it, its another degree of safety and can hurt at all. Any extra safety measures is always a plus in my book.


If an insert has a ss liner, as mine does and it extends all the way up my chimney and out the top, how would the fire get out of it into the chimney proper?? My understanding is that a chimney fire, if it were to happen, in an insert with a liner would be contained in the liner and wouldn't get into the masonry part of the chimney at all.

I am getting conflicting info. in regards to if one is necessary with a full liner. I do have one at the top of my chimney which is where most people say one is a necessity.

It just seems to me that one isn't as necessary with an internal chimney and a fully lined insert.

So I'm back to the forum for more personal input from those of you who have had experience with a lower block off plate as well as having not had one previously. What have you found in having it both ways?

My installer came yesterday to inspect chimney and fireplace and said all looks ok for install of the Jotul 550. I asked him about the lower plate and he said it wasn't necessary due to how my set up is.... He is a full time fireman as well as an installer.....I'm befuddled so I figure just what I need is more info!
Ask the installer/fireman why would he advise against an added safety measure. He won't tell you that a block off plate is a PITA to install, and he won't make enough off it for the hassle. Ask him if the liner does take over 2100 degrees from a chimney fire for longer than testing standards, and the liner does for whatever reason fail............... what will stop the fire from back drafting back into the house at bottom without block off plate?
Bottom line, is if you can sleep ok at night, with you wife/kids/ yourself, and not worry, then don't sweat it and leave it off.
Personally, if a fireman or anyone for that matter came to install my insert, and told me I didn't need an extra added benefit of protection, I don't think I would be as comfortable with them installing my insert.
Per the manual if the liner is run all the way up, a block off plate is not required. (Only a direct connect requires per manual. But a go back to an extra added safety measure. Up to you.
Good luck with the install, and send pics

 

[Hogwildz]

First off, don't get yerself in a tizzy LOL. Take some breaths and just relax. You use furnace cement around where the liner passes through the block off plate & hi temp RTV silicone caulk (both can be found at Lowes, HD or any hardware store) around the perimeter where the block of plate meets the walls of the old fireplace. If the gap around the place where liner comes through is large, you can fit it with some stove door rope gasket to fill the gap (thanks to Brother Barts great advice). Block off plate can be installed anywhere between just below the damper & just above the lintel. You can have him cut a lil more out of the damper area for a straighter shot for liner at the stove outlet if you want. Would make installing easier. The flat sheet galvanized they sell at Lowes or Home Depot will due just fine. Its about $7.00. I made mine & Newtown's on site with the sheet metal, tin snips and a set of small hand metal brakes. It does not show after install is complete, so it does not have to be a thing of beauty. If need be, let the installer know he can do it in as many pieces as he needs to form the plate. I used 3 myself due to lack of work room in the area here. I used 2 at Newtown's place with a ring to go around the liner to fit snug to it. Let us know how it goes, and post some photos.

 

[begreen]

24 gauge sheet metal will work fine.

 

[jadm]

Install date is set for Feb. 11 - weather permitting. I looked at the 'how to' info. for doing the pictures and it looks easy enough. I will have my 11 year old take the pictures because he really likes doing that kind of stuff and then he can transfer them onto the computer - I have no idea how to do that yet but it looks like I have a perfect opportunity to learn!! If I need help putting them onto the forum site I'll see if my 18 year old will help. He's pretty computer savy but not always willing to help his mother out...He's balanced precariously at that adolescent jump off point into independence which, translates into, somedays he acts human and on others I wonder who it is standing in front of me...One way or another, pictures will be forth coming after all of this prep. is finally finalized!!

Thanks for the help!

 

[RingDing]

I had a big problem with my install and I attribute it to not having a block plate installed. The problem was excessive moisture condensing and forming mold in my attic under the roof decking.

My chimney contains 2 separate flues - one for the furnace and one for the fireplace. Years ago I realize too late that I had a blockage in the flue serving my furnace. My furnace, equipped with an exhaust blower, couldn't vent properly so the exhaust worked it's way in and around the clay tile until it vented through the chimney top. The mortar inside the chimney eventually degraded by the acidic condensate in alot of spots and especially in the attic wall causing, in some of cases, open joints in the chimney and brick wall inside the attic. I eventually realized the situation and had it fully relined with stainless steel and had the fireplace relined, too, and installed an insert all at once.

Then after firing up the insert I notice mold days later in the attic under the roof decking. I believe the annular space between the fireplace reline and existing chimney got hot enough and, therefore, induced a draft that pulled warm moist air from inside my living room inside the chimney. Having nowhere else to go, because the installer put a block off plate at the chimney top, the warm moist air escaped thru some open mortar joints into my attic and condensed on my cold roof decking.

I had a pain in the neck job of pointing and stuffing insulation around the wall in the attic to try and block the air flow. Never really was able to stop the problem. Had to rig some power fan up there to help things. Out of sight out of mind right now.

The house is old and made of brick. The insert faceplate doesn't create an airtight seal at the fireplace opening. Not sure if a block off plate would have solved the problem but I think it would have helped. Installer used rock wool instead of a plate. I never put one in afterward because the installed had a really hard time putting the insert in. I was alway afraid to remove it for fear that it wouldn't go back in easily enough.

None of my local fireplace shops heard of this type of problem.