Blocking plate? Yes or No

[sticksnstones]

Hello all, I am currently installing a Hampton HI300 in existing masonry fireplace. Specs: flu is 30' tall interior chimney. I've already installed the stainless smoothwall 6" liner. The liner is wrapped with 1/4" insulation for the first 8' down from the top. I couldn't get any further down because it was getting ripped to shreds on its way down beyond that. From the top I jammed in about 2' - 3' of roxul between the clay flu and the liner so it is sealed pretty tight up at the top.

I have read the 2 schools of thought on this terrific forum about whether or not to install blocking plates and would like to know what the consensus opinion is on my specific application for whether or not I should use a blocking plate for my install. FYI, I plan to make a good seal around the inserts façade so not too much air can slip by that way.

 

[DAKSY]

I would DEFINITELY block the damper area of an exterior fireplace, but I might
see how that Hampton heats with an unblocked interior one.
Once the masonry has heated up, you may be able to warm some of
the interior surrounding walls...Not a bad thing to do...

 

[Dmitry]

When I installed my insert I stuffed as much Roxul insulation as I could in my chimney above my insert just like they recommended in a manual . Later I did more research and learned that block off plate prevents air leaks and insulation prevents heat transfer . The one is not a substitute for another. Do the block off plate, Just do it
Same way , when you insulate your attic you can't just throw insulation in it , you have to seal all gaps and holes to prevent air from escaping.

I'm not sure why you want to seal the facade of insert. Airseal the chimney and let the hot air from insert cavity enter the room.

 

[sticksnstones]

When I installed my insert I stuffed as much Roxul insulation as I could in my chimney above my insert just like they recommended in a manual . Later I did more research and learned that block off plate prevents air leaks and insulation prevents heat transfer . The one is not a substitute for another. Do the block off plate, Just do it
Same way , when you insulate your attic you can't just throw insulation in it , you have to seal all gaps and holes to prevent air from escaping.

I'm not sure why you want to seal the facade of insert. Airseal the chimney and let the hot air from insert cavity enter the room.

Thanks for your experience and suggestions on the topic. The "seal" around the façade is the manufacturers instruction. They instruct to lace the inner edge of the façade parts with a fluffy layer of gasket around the backside of the outer edge of the façade parts.

 

[bholler]

Thanks for your experience and suggestions on the topic. The "seal" around the façade is the manufacturers instruction. They instruct to lace the inner edge of the façade parts with a fluffy layer of gasket around the backside of the outer edge of the façade parts.

That insulation does next ot nothing to stop air flow and does absolutly nothing to keep the heat from rising up the chimney. You want a block off plate to get as much of the heat into the room as you can

 

[sticksnstones]

When I installed my insert I stuffed as much Roxul insulation as I could in my chimney above my insert just like they recommended in a manual . Later I did more research and learned that block off plate prevents air leaks and insulation prevents heat transfer . The one is not a substitute for another. Do the block off plate, Just do it
Same way , when you insulate your attic you can't just throw insulation in it , you have to seal all gaps and holes to prevent air from escaping.

I'm not sure why you want to seal the facade of insert. Airseal the chimney and let the hot air from insert cavity enter the room.

Basically it would seem to me that if you blocked the air from around the edges of the façade (like the mfr suggests) you effectively block the draft that would go up where the blocking plate would be. The thing that festers for me is that I've read many on this much respected forum be of the opinion that a block off plate leaves the chimney exposed to more moisture decay because no heat gets up there to dry out condensate moisture. This is what I've gathered so far and welcome rebuttals/ideas to these observations.

 

[jophysx]

I have a Hampton HI300 as well. Mine is in an exterior chimney. I burned for two or three years with no blockoff plate. Then last year I went the route of stuffing roxul up the flue to prevent hot air and heat from escaping up into the chimney space. I think the roxul is just as effective as a fabricated blockoff plate, and much easier. I also installed some roxul along the interior of the fireplace to prevent heat loss through the masonry. I noticed a significant improvement in burn characteristics - longer burn times, ability to sustain secondaries for a longer time at a lower burn rate, greatly reduced ash production.

I am very happy I did it and would never go back. In your case, with an interior chimney it may not make quite such a big difference, but I would do it if I were you.

-Jim

 

[BrotherBart]

I must have missed those posts about exposure to moisture decay. Much less many of them.

 

[bholler]

Basically it would seem to me that if you blocked the air from around the edges of the façade (like the mfr suggests) you effectively block the draft that would go up where the blocking plate would be. The thing that festers for me is that I've read many on this much respected forum be of the opinion that a block off plate leaves the chimney exposed to more moisture decay because no heat gets up there to dry out condensate moisture. This is what I've gathered so far and welcome rebuttals/ideas to these observations.

Well if the insulation did actually seal if would help but the heat would still rise. And there will still be a decent amount of heat coming off the liner even if it is insulated like it should be. So that will drive out any condensation. And if you do seal it off and keep the moist air from the house from getting up there you will have much less condensation

 

[cookin2night]

Install the block off plate. It keeps the fire box hotter which in turn keeps the flue hotter which in turn creates less creosote. Make sure you insulate your flue as recommended.

 

[GS7]

Hello all, I am currently installing a Hampton HI300 in existing masonry fireplace. Specs: flu is 30' tall interior chimney. I've already installed the stainless smoothwall 6" liner. The liner is wrapped with 1/4" insulation for the first 8' down from the top. I couldn't get any further down because it was getting ripped to shreds on its way down beyond that. From the top I jammed in about 2' - 3' of roxul between the clay flu and the liner so it is sealed pretty tight up at the top.

I have read the 2 schools of thought on this terrific forum about whether or not to install blocking plates and would like to know what the consensus opinion is on my specific application for whether or not I should use a blocking plate for my install. FYI, I plan to make a good seal around the inserts façade so not too much air can slip by that way.

I've had my Hampton HI 300 for 4 years. Chimney is on an exterior wall. At the time of the install I didn't know much and trusted the installer/dealer who said insulation wasn't needed on the liner, damper hole area, or around the stove facade. The stove burned great every year but what could I compare it to being new and not knowing better? When I wasn't burning TONS of cold air leaked into the room. It was really bad. Discovered the block off plate method here on hearth last season. Just installed a block off plate days ago.

1. I first cleaned the chimney with a product called soot eater I found on amazon. (First year I didn't pay to have it cleaned).
2. After cleaning from the bottom I went on the roof to look down the liner with a flashlight to see how I did. Worked real well.
3. I used high temp silicone to seal gaps around the top of the liner under the raincap.
4. At the bottom I stuffed Roxul insulation made for crawl spaces to resist moisture, until I could stuff no more in the damper hole area.
5. When the wind blew enough to move tree branches, I taped toilet paper strips from the mantel to hang just above of the stove. I did this with the facade removed of course. There was no movement at all so I believe It's sealed well. That hanging toilet paper would move with the facade on, before the insulation was added.
6. I bought 26 gauge shiny sheet metal from Lowe's to make a block off plate.

With the air sealed, insulation in place, and shiny sheet metal reflecting heat back to the stove I can't wait to see if I find improvement in performance beyond plugging up that awful cold air leak. We'll see... Now it's time to get that new door gasket changed so I can make a fire!

 

[iluvjazznjava]

I've had my Hampton HI 300 for 4 years. Chimney is on an exterior wall. At the time of the install I didn't know much and trusted the installer/dealer who said insulation wasn't needed on the liner, damper hole area, or around the stove facade. The stove burned great every year but what could I compare it to being new and not knowing better? When I wasn't burning TONS of cold air leaked into the room. It was really bad. Discovered the block off plate method here on hearth last season. Just installed a block off plate days ago.

1. I first cleaned the chimney with a product called soot eater I found on amazon. (First year I didn't pay to have it cleaned).
2. After cleaning from the bottom I went on the roof to look down the liner with a flashlight to see how I did. Worked real well.
3. I used high temp silicone to seal gaps around the top of the liner under the raincap.
4. At the bottom I stuffed Roxul insulation made for crawl spaces to resist moisture, until I could stuff no more in the damper hole area.
5. When the wind blew enough to move tree branches, I taped toilet paper strips from the mantel to hang just above of the stove. I did this with the facade removed of course. There was no movement at all so I believe It's sealed well. That hanging toilet paper would move with the facade on, before the insulation was added.
6. I bought 26 gauge shiny sheet metal from Lowe's to make a block off plate.

With the air sealed, insulation in place, and shiny sheet metal reflecting heat back to the stove I can't wait to see if I find improvement in performance beyond plugging up that awful cold air leak. We'll see... Now it's time to get that new door gasket changed so I can make a fire!

Let us know how it goes. I too am contemplating a block off plate

 

[Smoked]

I did 2 this summer in exterior fireplaces. Probably a days work total and $100 in materials. Metal fab is not my gift but ... Roxul was about $45 and was enough to do 6 fireplaces so if you could find a smaller batch or someone with some left over close that could save you something. I angled mine up from back to front hoping any convection off the stove and tee will flow out instead of getting trapped in the damper area. I think it is a no brainer to do it.

 

[mass_burner]

My installer is coming tomorrow to finish the job. He made block off plate but hasn't mentioned roxul yet. Its an interior chimney, fireplace in basement. Do I need it?

 

[davidmsem]

My installer is coming tomorrow to finish the job. He made block off plate but hasn't mentioned roxul yet. Its an interior chimney, fireplace in basement. Do I need it?

I would add the Roxul.....traps so much energy. So easy to do while you are there.

 

[Fastdonzi]

I too made a Block Off Plate this year ( 60" wide x 24" deep). Bought the Huge Bundle of Roxul, Only used two Slabs. So the Block Off Plate has about 5" thick insulation on top of it... Has to be better than No Block Off Plate.....

 

[jharkin]

Well if the insulation did actually seal if would help but the heat would still rise. And there will still be a decent amount of heat coming off the liner even if it is insulated like it should be. So that will drive out any condensation. And if you do seal it off and keep the moist air from the house from getting up there you will have much less condensation

Common misconception. Heat does not rise, it radiates in all directions equally in proportion of temperature differential. Hot air does rise (relative to another cold air mass) so the blockoff plate makes a big difference.


Daks makes a good point about interior chimneys warming the walls, and this is the reason why center chimney houses where commonly built in cold regions before the advent of central heat... Problem is that once you start sealing up and insulating that can have unintended consequences. Case in point - my wood stove is hearth mounted on an interior chimney. Block off plate and liner to the top of the brick chimney. Even with that all the heat soak into the fireplace mass and heat off the liner keep the entire chimney quite warm all the way through the roof line. In the dead of winter with subfreezing temps Ive measured 50-60F surface temp on the chimney inside the attic - this warms my roof and contributes to ice damming. Ive gone so far as to wrap the outside of the stack with Roxul inside the attic to help.

200 years ago this was not a problem as so much heat leaked through the attic floor the entire roof was warm and all the snow melted anyway. Today its a huge problem and Ive had to deal with a lot of ice damage when the chimney melts snow that reefreezes lower down the roof slope.

 

[GS7]

My installer is coming tomorrow to finish the job. He made block off plate but hasn't mentioned roxul yet. Its an interior chimney, fireplace in basement. Do I need it?

I'd add the roxul while the area is open. Better to keep the warm air inside the home as long as possible.

 

[bholler]

Common misconception. Heat does not rise, it radiates in all directions equally in proportion of temperature differential. Hot air does rise (relative to another cold air mass) so the blockoff plate makes a big difference.

Ok i should have said the heated air will rise but regardless you will be sending heat up the chimney and not into your room.

 

[GS7]

I've had my Hampton HI 300 for 4 years. Chimney is on an exterior wall. At the time of the install I didn't know much and trusted the installer/dealer who said insulation wasn't needed on the liner, damper hole area, or around the stove facade. The stove burned great every year but what could I compare it to being new and not knowing better? When I wasn't burning TONS of cold air leaked into the room. It was really bad. Discovered the block off plate method here on hearth last season. Just installed a block off plate days ago.

1. I first cleaned the chimney with a product called soot eater I found on amazon. (First year I didn't pay to have it cleaned).
2. After cleaning from the bottom I went on the roof to look down the liner with a flashlight to see how I did. Worked real well.
3. I used high temp silicone to seal gaps around the top of the liner under the raincap.
4. At the bottom I stuffed Roxul insulation made for crawl spaces to resist moisture, until I could stuff no more in the damper hole area.
5. When the wind blew enough to move tree branches, I taped toilet paper strips from the mantel to hang just above of the stove. I did this with the facade removed of course. There was no movement at all so I believe It's sealed well. That hanging toilet paper would move with the facade on, before the insulation was added.
6. I bought 26 gauge shiny sheet metal from Lowe's to make a block off plate.

With the air sealed, insulation in place, and shiny sheet metal reflecting heat back to the stove I can't wait to see if I find improvement in performance beyond plugging up that awful cold air leak. We'll see... Now it's time to get that new door gasket changed so I can make a fire!

Let us know how it goes. I too am contemplating a block off plate

Ok, I finally put the new door gasket in. Last night was on the chilly side so I had the first fire of this season with the new block off plate installed. I know the true test with the block off plate will be when it's really cold and windy later in the season but...One thing I know for sure right now is the block off plate with the roxul insulation gets the stove hotter faster, and keeps it hot longer. Zero cold air infiltration now. I think the block off plate with insulation should be the standard.

 

[robk]

Does the plate and insulation do anything that would interfere with a permit and inspection?

 

[begreen]

No.

 

[cookin2night]

Does the plate and insulation do anything that would interfere with a permit and inspection?

No

 

[robk]

Great!

The guy that is helping me (or the guy that is doing it and I'm helping) said he had the sheet metal to do it and would help make the plate but he wasn't sure about code. None of the guys I'd talked to had even heard of one.

 

[cookin2night]

Great!

The guy that is helping me (or the guy that is doing it and I'm helping) said he had the sheet metal to do it and would help make the plate but he wasn't sure about code. None of the guys I'd talked to had even heard of one.

I drilled with a mason bit then used mason screws to hold mine up and caulked with high temp caulk to seal the cracks. I did that from the beginning so I don't have a reference to no plate but I also put insulation around the line with the mesh and roxul over that. Last year I only had to clean my cap once from burning 24/7 and my living room was always around 74f. When I swept the liner over the summer I had less than a coffee mugs amount of creosote built up. Good luck