Block Off Plate

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DianeB

DianeB

Feeling the Heat
Apr 26, 2012
399
Foot Hills of the Berkshires
Our stove connects to our fireplace chimney with a Rear Pipe & T with the stainless pipe passing through what used to be the fireplace damper area. The area is sealed off with a block off plate. I am wondering if I should insulate around that block off plate. When I look up to see the plate, it appears the stainless pipe was crimped a bit to pass through the plate...appearning more oval than round.

Our old stove also was connected the same way I beleive but without the block-off plate, with just insulation up around where the pipe entered the damper area. For our old stove, we had a local mason install the stainless liner after a chimney fire.

We have a totally brand new fireplace and chimney now because of storm damage last year and went with a new stove. I ask because I wonder about heat radiating behind the stove and escaping up through the chimney. I saw the block off plate installed and it was just a pretty thin piece of metal.
 
Not sure what's typical, but my chimney guy stuffed insulation into the chimney space around the liner before installing the block-off plate.
 
I have Roxul stuffed around my liner then the block off plate, made a huge difference.
 
I recently did the block off plate and insulation for my insert, and while I can't see any difference in performance (I wasn't having problems before), there is a big difference when it's not running. Previously I had a huge cold air draft coming down the chimney, now its gone. It costs almost nothing in materials, and even if it doesn't improve anything, I've never read about it causing any problems, so there is nothing to lose. $40 for Roxul (although you only use $4 of it), $6 for steel sheet and a fistful of self-tapping screws. I put the Remaining Roxul to good use elsewhere.

TE
 
I stuffed Roxul around my liner and made a block off plate with the Roxul and I noticed this cured my over draft issue for what ever reason, this made my stove much easier to control.
 
TradEddie said:
I recently did the block off plate and insulation for my insert, and while I can't see any difference in performance (I wasn't having problems before), there is a big difference when it's not running. Previously I had a huge cold air draft coming down the chimney, now its gone. It costs almost nothing in materials, and even if it doesn't improve anything, I've never read about it causing any problems, so there is nothing to lose. $40 for Roxul (although you only use $4 of it), $6 for steel sheet and a fistful of self-tapping screws. I put the Remaining Roxul to good use elsewhere.

TE
Click to expand...
If your stove was doing a good job of heating your house before the BO plate you probably wont notice a difference, in my case the stove was doing about 75% of the heating, with the block off plate that number is now higher, not sure what % yet but it did raise the temp in my office 3 degrees.
 
I won't be able to remove the blockoff plate to put the roxul in the cavity, but do you think I could just stuff it up around the block off plate brakets and hope that it stays up around where the hole is cut into the plate and where the pipe enters? Would it do any harm if it fell down on the T?
 
I know it may not look real nice but I removed the top surround cover to my insert to let the extra heat out and that really works! Since doing this it made rethink the idea of how far my insert is in the fireplace........
 
weatherguy said:
If your stove was doing a good job of heating your house before the BO plate you probably wont notice a difference, in my case the stove was doing about 75% of the heating, with the block off plate that number is now higher, not sure what % yet but it did raise the temp in my office 3 degrees.
Click to expand...

My insert runs 1-2 days per week at very most, so the air sealing was my motivation, gaining efficiency when running is just a bonus.

TE
 
DianeB said:
I won't be able to remove the blockoff plate to put the roxul in the cavity
Click to expand...

Why is that? Heck, most block off plates are really there to rigidly hold up the insulation. (so it can't fall down.)
 
More importantly is the question of is there a liner running all the way to the top, or is that set up just a slammer install.
I'd be more focused on that first.
 
No slammer now. Well built fireplace and chimney by a craftsman, stainless liner installed by stove co. Our old stove was installed in 1979...about 5 ft of stove pipe up into the masonry chimney - it lasted for 20 years until the fire then a stainless line. Now a totally rebuild fireplace and chimney because of storm damage...
 
Good to hear.
I installed a block off in mine, and am glad I did. More heat kept from going up and dispersing out the masonry, is more heat in the house.
 
When I moved into this house, I found the previous owner had burned this stove for 20 years with a 6" stovepipe extending two feet up into an 8" clay tile chimney. The 1" space around the stovepipe was packed solid with creosote. How it never caught fire, I will never know. We actually burned with it that way (unknowingly) most of our first year, as the home inspector and chimney inspector both missed it.
 
DianeB said:
No slammer now. Well built fireplace and chimney by a craftsman, stainless liner installed by stove co. Our old stove was installed in 1979...about 5 ft of stove pipe up into the masonry chimney - it lasted for 20 years until the fire then a stainless line. Now a totally rebuild fireplace and chimney because of storm damage...
Click to expand...

Dianne,

Not far from you in the town of Petersburgh, NY over the pass on the NY side. I just put in an insert and used the Roxul over the blocking plate with new SS liner. Makes a big difference for me as well. No more draft and this room is now the warmest in the house when it used to be the coldest. Found the bag of Roxul at Lowes and like you only used one batt then luckily was able to sell the remaining 11 batts to a guy at Curtis Lumber for $25. Entire bag cost $39. Good luck. Now working how to best distribute heat from the room with the insert to the rest of the house. Did you use the plan for the blocking plate from this site? I did and have actually passed it on to a friend.

Ken
 
I did not yet install a blocking plate when I installed my Avalon Olympic into my fireplace w/a 22' S.S. Flex duct. I will do it in the spring when heating season is over. I regret not taking the extra time.

I know I am losing alot of heat up the chimney, oh well, live and learn
 
That's a lot better than never learning!
 
Better late than never. If you get it done and it is a noticeable difference, you will be all smiles and warmer.
 
12pack said:
I did not yet install a blocking plate when I installed my Avalon Olympic into my fireplace w/a 22' S.S. Flex duct. I will do it in the spring when heating season is over. I regret not taking the extra time.

I know I am losing alot of heat up the chimney, oh well, live and learn
Click to expand...
I didnt install mine til this year and I got the insert 4 years ago, your way ahead of my.;lol I didnt think it would matter much as I have an interior fireplace but it keeps more heat in the living area than up the flue and absorbed by the huge stone fireplace structure.
 
I spoke with a Roxul rep at Lowe's yesterday. Had a hunk of the insulation sitting in a pan of water all day and it wasn't wicking up moisture. Also had another piece with a blow torch blasting on it. No change. I think I'm going to stuff the insulation up above my insert installation, then line it with heavy duty aluminum foil (melting point 1220 deg F) to help keep it in place, maybe easier than making a BOP. Saw these neat rigid wires used to keep insulation up between joists when you're insulating above your head in a house. They friction fit between the joists. They make 24" ones, I think they'd be good for holding the insulation up.
 
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