blockoff plate with insert installed

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gilmil

Member
Dec 1, 2010
49
Central CT
Local dealers wouldn't do a blockoff plate on our 30' external chimney. They supposedly did one at the top, and I know they used an insulated liner. I'm mechanically inclined and a tinkerer, I have no doubt that a blockoff plaate and stove install is within my abilities. (I didn't want to install the liner in our chimney because it's an 8*12 and the 5.5" insulated liner would have been brutal to get down. To me it was worth paying someone with insurance to install it.)

So now that the stove's in of course I'm getting sub standard results, good burn temps but cool rooms. First thing I'm going to do is fill air gaps in the house, next is install a blockoff plate. I have a good 9" above firebox to work with the HI300 in place. Think I can sneak a 2pc blockoff plate in there?

-Gil
 
I installed my rockwool and steel block off plate with the insert in place. I have about the same amount of room, maybe a little more, and didn't have much trouble. The difference is I didn't use tapcons, or masonry fasteners, to hold it in place. I figured since it's an insert with a surround who cares if it looks perfect benind it. I made the plate fit nice and snug with the insulation above it and then cut some steel tube the right length to wedge it up between the fireplace floor and the blockoff plate. No drilling or screwing required and if I take it out I can simply kock the pipe loose and remove the blockoff plate. Not perfect but much better than a huge hole.
 
I like that idea. Did you make it a 2 piece plate ?
 
I have a two piece blockoff plate that I fabricated myself, I used Tapcon screws and furnace cement to try to make it as airtight as possible. It has rockwool behind it as well. Works very well and eliminates the need to try to get an airtight surround around the insert.
 
Yes, I used a two piece plate but I didn't make it split in half. Below in the pictures you'll see how I knotched the plate to slide in and around the chimney liner. The first picture shows the rockwool insulation fitting very snuggly in the damper area. I cut it a little big and actually had to hammer it in place. The stuff is pretty stout since its 2" thick and it held itself up without any problems. I did not make my blockoff plate with beveled sides, only the back. The front is wedged very tightly against the angle iron and the sides just fit flush with the brick. In the pictures you'll see where I was test fitting the plate and a piece of wood on the left side is holding the plate in place, that is where the steel pipe is now that it's done. I didn't caulk it yet but easlily could. To fill the gap where behind the chimney liner, in the plate, I just cut a long rectangle of sheet metal and used that to span the missing area. On both sides of the "missing piece" is where the two vertical pipe sections are that hold the entire plate in. I will say if you don't have everything fitting snug this probably wouldn't work. I also used heavy guage sheet metal so it doesn't bow anywhere either. It's far from perfect but I doubt I'll be in this house for a long period so it seemed a little less permanent. I may not caulk it since everything fit so snug and the insert is heating my house fine. I have much bigger air leaks to take care of before I worry too much about the small ones.
 

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Here it is with the plate. Pics were too big to fit in one post and I don't have time to screw with them. And, yes I like furnace cement everywhere! hahaha
 

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I just did a two piece block off for a friend with a Lopi Declaration, we put rock wool in above it as well. It fit snug everywhere around the perimeter and we ran two tapcons in each half to hold it inplace until the hi temp silicone dried. It probably would have been fine with just the silicone once it was dry but we wanted to put everything together and fire it up.
 
It looks like the installers hacked apart the fireplace firebox to get the insert to fit. They didn't do a visit and believed my measurements (how foolish). There are numerous fire bricks missing from the back of the fire box. I would have taken an angle grinder and notched the bricks a bit to get the insert to fit. I wouldn't have taken them completely out. Oh well such is life!

I guess I'll have to come up with a 3 piece block off plate. One to go up the back of the fire box where the bricks are missing and the other two pieces to go around the chimney liner. Without the insert going you can really feel the cold air rip down the chimney.
 
when I said I wantd a block off plate the installer told me that the one he put at the top was fine, NO I want a block off so he brought in many pieces of about 1/8"metal(tin?) and put them together and cut them around the pipe. NOt sure why he did not just take two big pieces and cut to fit but the smaller ones he used and stuck together do work and they have some kind of insulation he poped adn it sort of exploded it the opening which of course was done before the block off plates. Works
 
sandie so ur saying the block off plate makes a big difference ? my installer said the same thing he blocked off the top part of the 30 foot chimney, i asked for him to install a block off plate above my merrimack and he quoted me 475 bucks. at this point i was thinking to just jame installation between the merrimack and where the damper was...



Anyway anyone know where to get rock wool from, i cant find it in the stores around here and my online search hasnt been productive.
 
micaaronfl said:
Anyway anyone know where to get rock wool from, i cant find it in the stores around here and my online search hasnt been productive.

Do they have a carter lumber close by? Thats where I got mine (Roxul AFB).
 
Do you have a little mom and pop hardware store? How about a stove shop? I got mine from the little mom and pop hardware store. $8 for a 2*4 sheet.

Now if I could just figure out how to make the blockoff plate with the insert in place.
 
gil said:
It looks like the installers hacked apart the fireplace firebox to get the insert to fit. They didn't do a visit and believed my measurements (how foolish). There are numerous fire bricks missing from the back of the fire box. I would have taken an angle grinder and notched the bricks a bit to get the insert to fit. I wouldn't have taken them completely out. Oh well such is life!

Oh boy. I imagine it's been done many times, but as I understand it the fireplace is supposed to be intact for the insert to meet code. You might want to start another thread to get some info on that.

I have an insultated block-off plate above my insert, infact I insulated over the fireplace walls with rockwool & sheet metal which is admittedly a bit of overkill. I don't think you'll see a night& day difference, but definitely worth doing to me.
 
The installation passed inspection. I can re-brick part of the fireplace with fire bricks, but there's still gotta be some removed for the liner to fit through. It's my understanding that as long as they put a plate in the fireplace that it's not usable it's fine.
 
$475 is WAY too much for the block off plate to be placed. Chimney sweep should do it and for maybe $100 at most.
 
Well due to constraints of insert/firebox/fireplace relationship a blockoff plate is almost impossible to fashion. I'm sure this summer I can pull the insert and try to fashion a blockoff plate. Tollerances are very tight, mainly due to the way the install guys did things and the nature of my 1929 fireplace :) I shoved an entire 2*4 sheet of rockwool up around the damper area, but couldn't fashion a piece of sheet metal to fit it. Maybe I'll have a chimney sweep fix it up for me....
 
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