block off plate dilema

[chipster314]

I had the pre installer over today and he has no problem if I make up a block off plate but what he recomended was just putting some Roxxul insulation around the pipe and old damper opening. Will this work? seems like it would have a better R value for allowing the heat to rise. He remembers when they use to use block off plates when the liner only went so far up the flue but now with a full liner and sealed cap not critical for drafting. But I do agree with the theory that no sense heating the old flue up. So will the Roxxul be good enough? Or do both? Also non inulated line. Would you spring for the insulated or is this beyond what is needed

Thanks

 

[Hogwildz]

If the gap between the liner and damper is small, I would use the rock wool to fill the gap. If its a large gap, then make a block off plate, you can insulate the top of it or not.
As far as insulating the liner, most will tell you if its an interior chimney, no insulation needed. If its a chimney on an exterior house wall, insulate.
Of course insulating is one step to improving draft.

 

[chipster314]

I have already made a cardboard template just below the old damper, if I go the plate route.

I just measured and the opening is 4 1/2" x 25" hence why he said they would flatten out the liner a little to get it through hole. This brings up the next question, is it ok to flatten the liner out or should I make them take out the frame also for the old damper?

The chimney is on the outside wall, so what does putting in a insulating pipe do for me, what gains are there. What I understand is you would only lose a little heat at the start of the burn but once it is going the liner is going to be hot and I dont see how you are going to loose any heat as you are blocked off from the rest of the flue with blocking plate or insulation
Thanks

 

[Rudyjr]

Its pretty easy to open up part of the damper throat with a 4 inch grinder and cut off wheel. I put in the Roxul or rockwool with the block off plate and around the liner at the cap. My chimney sweep said that the rock wool would be better with something holding it in place. The block off was real easy to make and install.

 

[Hogwildz]

Cut the damper out enough to allow the liner to remain round and pass through.

 

[BrotherBart]

Cut the damper out enough to allow the liner to remain round and pass through.

What he said.

 

[chipster314]

OK will try to cut out damper to give me enough space. Can I use the Roxxul or should I get something more specific to high heat, and if so what and where?

Also how thick does the block off plate need to be? And can I use hight heat silicon to seal the edges or do I need something else. I think we have 400 degree silicone at work.

 

[chipster314]

I also wonder if there would be a problem with installing the blocker plate a little lower and coming out flat in order to screw it to the under side of the steel lintel, but using the angled edges every where else?

 

[Cedrusdeodara]

well, the last thing you stated is exactly how I am fabricating my blockoff plate. I am doing a 2" flange on the back and two tapered sides (trapazoid shape), but the front is flat and will be directly screwed into the back/bottom of the lintel. But, I'm new to this so don't write it in stone. I will be packing some ceramic wool above the plate and around the edges where it meets the firebox. The only mod that I may have to contend with is widening the flue cutout if it occurs where the stainless flanged attachment is, instead of the the sleeve.

Best of luck,
Brian

 

[Hogwildz]

I am not familiar with Roxxul, what is its heat & flammability rating?
I reused the rock wool that was in the previous block off plate for the previous insert.
If I didn't have that already I would have went with the block off plate alone.
You can purchase pcs of it online and prolly on ebay.
The plate can be made of the galvanized flat stock Home Depot or Lowes carries in their duct work isle.
I think its 26 gauge. What they have is fine. Yes you can install it a little lower if it makes it easier to install.
Seal the perimeter of the plate at the fireplace walls with high temp silicone. Seal the gap around where the liner passes through the block off plate with Rutland furnace cement or other furnace cement.
Try to keep that gap as small as possible, anything over 3/8" and the cement might crack and fall out.
Brother Bart gave an excellent suggestion of stuffing stove door rope gasket in the gap if it fits.
Its easiest to cut the whole in the plate, run the liner through, anf use a smaller round or square plate with more exact hole and a slit to slide it over the liner and into place then screw to the main plate.
It has to be effective, not purdy.

If you search Iceman's posts or PM him, he has some excellent photos of the block off plate installation he did.