block off plate?

[scjotulman]

I think I know the answer. I have a Jotul c450 insert with a fully insulated lined flue in an exterior chimney. I plan to install a block off plate but haven't had the chance. We had relative ( don't laugh all you northerners ) cold temperatures for South Carolina 16 degrees. I noticed that the insert didn't put out as much heat as normal. Is because most of the heat was going to warm the chimney? ls a block off plate more and more important the colder it gets?

 

[DAKSY]

I believe you already have proof of that. One reason is that you are heating the entire flue from the radiant heat off insert body. With a block-off plate, that radiant heat will get to the room when the masonry in the firebox heats up...

 

[EatenByLimestone]

Your house needs more heat to keep at a certain temperature when it gets colder. Your stove has to work harder to heat that and your chimney. It's time to let the fire go out and pull the insert!

Matt

 

[scjotulman]

I'm going to try and install without pulling the stove I have all my measurements and I'm planning on making a cardboard template to make sure it will fit before cutting it out of sheet metal. I hurt my knee and it still hurts to squat and bend it so I think I will have to wait until next weekend.

 

[Bones]

Don't forget the roxul on top of the block off plate....

 

[scjotulman]

Thanks for the reminder. I have it on my list.

 

[oconnor]

Don't forget the roxul on top of the block off plate....

Roxul on top isn't needed. You aren't trying to insulate, just create an air barrier. With the liner inside the chimney, it is way hotter on the flue side of the plate than the room side.

 

[Bones]

Roxul on top isn't needed. You aren't trying to insulate, just create an air barrier. With the liner inside the chimney, it is way hotter on the flue side of the plate than the room side.

How do you seal around the hole through the block off plate then to create an air barrier ¿

 

[Mr A]

How do you seal around the hole through the block off plate then to create an air barrier ¿

https://www.hearth.com/econtent/index.php/articles/making_a_block_off_plate/
This is about the best info I found when researching how to install my own insert. Once I got the flue through the chimney, I could't get the insert, the flue, and the block off plate lined up. The insert has to be in perfect position to accept the flue, and also positioned in the fireplace opening correctly to be able to bolt on the finish surround. I may try again this summer, but for now, I just stuffed the damper area with roxul around the flue. I also have roxul around the flue at the top of the chimney, nothing between. Most masonry chimneys with terra cotta liner are built with 1 inch space between the bricks and terra cotta, filled with sand, of course there is no way to verify without digging into the masonry work to take a look

 

[weatherguy]

You should have no problem making the block off plate with the insert in place, a few of us have done it that way, its a couple extra steps but a lot easier than pulling the insert.

 

[Bones]

https://www.hearth.com/econtent/index.php/articles/making_a_block_off_plate/
This is about the best info I found when researching how to install my own insert. Once I got the flue through the chimney, I could't get the insert, the flue, and the block off plate lined up. The insert has to be in perfect position to accept the flue, and also positioned in the fireplace opening correctly to be able to bolt on the finish surround. I may try again this summer, but for now, I just stuffed the damper area with roxul around the flue. I also have roxul around the flue at the top of the chimney, nothing between. Most masonry chimneys with terra cotta liner are built with 1 inch space between the bricks and terra cotta, filled with sand, of course there is no way to verify without digging into the masonry work to take a look

That's how mine is installed....sealed at the top and block off plate with roxul on top of the plate to seal around the flue.

I would think ( scary) if it isn't sealed around the block off plate there would be no need for a at all....JMHO

 

[oconnor]

How do you seal around the hole through the block off plate then to create an air barrier ¿

Use Roxul around the hole of you like. The post mentioned Roxul above the plate, not sealing the plate to the liner.

 

[Snotrocket]

Use Roxul around the hole of you like. The post mentioned Roxul above the plate, not sealing the plate to the liner.

You seem to change your tune on this every other day.Here in this thread I'm about to link you went back and forth on me with it. So is it safe or not?

https://www.hearth.com/talk/threads...e-the-entire-length-of-the-flue.119872/page-2


To the thread starter. There is going to be a gap around the block off plate and without something behind it it's all but useless.

Myself and many other have used Roxul behind the block off plate with great results.

 

[oconnor]

You seem to change your tune on this every other day.Here in this thread I'm about to link you went back and forth on me with it. So is it safe or not?

https://www.hearth.com/talk/threads...e-the-entire-length-of-the-flue.119872/page-2


To the thread starter. There is going to be a gap around the block off plate and without something behind it it's all but useless.

Myself and many other have used Roxul behind the block off plate with great results.

I haven't "changed my tune". I used it as to air seal the damper around my liner.

Insulating behind the plate doesn't add value. The temp up there is likely 900*f or more. If anything, heat wants out.

Air sealing is different than insulating.

 

[Rudyjr]

Stuffed the extra Roxul from my installation above my block off plate on mine. Used what was left over from the piece that I had to go under the top cap around the liner. Was an easy way to seal around the liner where it passes through the block off plate. Seems to work well that way for me and has caused no problems.

 

[Hogwildz]

Door rope gasket works great around the liner where it passes through the block off plate.

 

[scjotulman]

Thanks for all the input. I think I will start off with the block off plate only then add Roxul if I feel it is needed.

 

[Mr A]

Thanks for all the input. I think I will start off with the block off plate only then add Roxul if I feel it is needed.

The plate is just a nice finished way to hold up the insulation(roxul) a piece of tin will not hold back the heat from going up the chimney

 

[Hogwildz]

The plate is just a nice finished way to hold up the insulation(roxul) a piece of tin will not hold back the heat from going up the chimney

If the block off is installed in the area tight enough and the gap sealed around the liner, it absolutely will keep a major amount of heat from going up the chimney cavity. Much more than just insulation stuffed into the the damper cavity.

 

[fitter9]

I installed a block off plate and roxul stuffed in the smoke shelf and above the plate over the weekend. It seemed to make a big difference. i have had my lopi freedom since october and I've noticed the surround has always been cold. i was going to wait till spring to do it but i had some extra time home due to the bad weather in jersey. I'm glad i did it now. the surround is now getting quite warm. (more heat going in the room than up the chimney.) the house is 3 - 4 degrees warmer than it was before the plate was installed. I'm getting an extra hour or two of useable heat out of a load of wood, i think thats because its taking a lot longer for the insert to cool down.
more heat and less wood seems to be what its all about. it cost me 150.00$ from H/D. it was that much because i has to buy a full set of made in USA tin snips. the plate seems to be well worth the money and effort.

 

[Snotrocket]

The block off plate alone isn't going to do jack.

There's a reason we insulate things. It's to keep an area a certain temperature.

It's just like an insulated liner. Why do people buy them? The liner itself is sealed all the way up so it must retain it's heat right? No, it doesn't do it nearly as well as when it's insulated.

I view my block off plate as what holds the insulation in.

 

[mellow]

I have not done a block off plate using sheet metal. I have however had one for a few years with just Roxul and found out I was still loosing heat to the outside brick. I have now installed half inch Durock as my block off plate and have Roxul on top of that for extra insulation, I no longer have the heat loss to the outside brick.

 

[scjotulman]

Update on my block off plate. I installed a block off plate this year. Didn't have to pull the stove. I didn't use insulation because I have had a water leak during the perfect storm that I wanted to fix first. I think I have found the source of the leak so that will be fixed. Even without insulation I have noticed a big difference. Tonight after reading some post here I decided to check the temperature of my chimney outside using my ir thermometer. Outdoor temperature was 29 degrees. The temperature of my chimney about 10 feet above my insert was 70 degrees. I think this shows the importance of using insulation above the block off plate. Has anyone else experienced this?

 

[Hogwildz]

The liner is going to put some heat into the masonry whether you insulate the block off plate or not. The plate will save a ton of heat from going up and out the masonry as you are now experiencing. Good choice to add the plate.