Blockoff plate vs insulation only blockoff...

tickbitty · Jan 29, 2014

I still haven't done a blockoff plate, though I think about it a lot! I notice that some folks have done the roxul only blockoff with wires or something holding it in. That would be an easier way out, because I'd have to remove the stove and disconnect it from the liner to do a plate. Plus, when my damper was taken out, two bricks were removed from the smoke shelf so that the insulated flex liner could fit through there. The level where the bricks are missing is pretty much on a level where the lintel is at the front of the fireplace, so somehow the blockoff plate would have to be fit on a slant or something so that it is even with the front and still covers that gap. Or I suppose I could make the plate on a level, minus the gap, and just stuff the 2-brick gap with roxul or something?

Back when we did the install (installer/friend balked at the blockoff plate) I did get a nice large bat of THICK Kaowool from a sculptor friend who works at a forge. Am I to understand that while Roxul is OK to leave exposed to some extent, Kaowool is not? The stove (which is an insert that sticks out a lot) does have a blower, and I don't want to leave any insulation uncovered unless it's safe, of course.

HybridFyre · Jan 29, 2014

You'll probably see some debate on it. My installers just shoved fiberglass insulation up there to block the drafts and gave me a hundred reasons why a blockoff plate and roxul wasn't necessary. Sadly I wasn't confident enough to not listen to them since they've done hundreds of installs. I do plan on pulling my faceplate in the spring and taking the insulation out and putting in roxul. but i'm in the same boat as you...not sure if i want to disconnect the liner and pull the insert to add a blockoff plate.

hamsey · Jan 29, 2014

Same boat here. Installer did not want to do it when he showed up even though I told him that I wanted it. He did stuff roxul up there. Not happy with the install at all. I contacted a certified installer that is coming to the house to take a look at things. I need some work done at the top of my chimney so I will have him install the plate. He know the importance of them and an insulated liner.

weatherguy · Jan 29, 2014

You don't have to disconnect or remove the stove to do a block off plate. I did mine last year and just did it in two pieces, easy peasy, there's some threads on how to do it without removing/disconnecting the stove.

tickbitty · Jan 29, 2014

weatherguy said:
You don't have to disconnect or remove the stove to do a block off plate. I did mine last year and just did it in two pieces, easy peasy, there's some threads on how to do it without removing/disconnecting the stove.

Yeah, I think I pretty much would though - I don't use a faceplate so I can see it, but the liner goes in at an angle and there is the issue of the missing bricks/odd shaped area and etc and if I am going to do it I'll have to take the stove out. That might not be the case for some folks but will be in mine, unfortunately. Now if I was stuffing roxul up there, I could prob leave it in place.

bholler · Jan 29, 2014

if it is visible we usually make cardboard templates to make sure it fits nice and tight it takes a few tries sometimes but cardboard is cheap and easy to work with and you can easily make a 2 piece plate look good

HybridFyre · Jan 29, 2014

bholler said:
if it is visible we usually make cardboard templates to make sure it fits nice and tight it takes a few tries sometimes but cardboard is cheap and easy to work with and you can easily make a 2 piece plate look good

Good advice. i have about a 2" gap to work with to shove my hands up there...that's the other issue. but i'm certainly going to give it a try!

Hogwildz · Jan 29, 2014

Insulation insulates, it does not block or stop airflow.

mstoelton · Jan 30, 2014

I had an installer tell me a block-off plate was un-necessary as well, but the instructions with my insert were clear - it is required. I followed directions on the forum to make a block-off plate and it fit like a glove.

I think installers tend to not want to take the time to measure, cut the plate to size, fit it in place, cut the hole and get the stainless liner through it. It takes extra time, and extra materials. The 20 ga. steel plate I had cut locally was $25.

In all it probably took and extra 2-3 hours to get the steel, mark it, bend the edges, test fit, cut the hole in the plate, fit the liner through it, get it in place, secure it with tapcons, and seal it with furnace cement.

For me it is well worth the knowledge that it is done right.

rwhite · Jan 30, 2014

I did mine in 2 pieces. The back of my fireplace was almost identical to yours. Will the bricks on either side of the 2 missing ones come out? I removed the entire run of brick and just rested the plate on top of those in the back of the firebox. I used a bit of adhesive that came with the liner to hold the insulation to the plate. Then I slid it into the firebox and rested on the back shelf and used self tapping screw to screw it to the lintel in front.

Lumber-Jack · Jan 30, 2014

I would do both. I would by a bag of the Roxul and tightly stuff half of it around the liner at the top, and the other half liner just above the the block off plate area.
If you stuff the roxul tightly it will insulate, but it will also help prevent the free flow of air up the chimney, it won't be perfectly airtight, but then nether will a block off plate unless you can get a perfectly fitting seal. Where you cut the round hole for the liner there is likely to be a bit of a gap, and unless you use some stove gasket cement when securing the metal to the brick there will likely be some air leakage.
Stuffing the roxul at the top will help keep the warmth in the chimney space and help keep the liner warm, and the warmer you keep your liner the better it will preform.

hamsey · Jan 30, 2014

Funny thing is, I had the plate installed. All that had to be done was cut out the hole for the liner. Going to cut a U out of it and see if I can get it into position. Also going to have an insulated liner installed over the summer. Was told that I do not need an insulated liner even though I was willing to pay the up charge. Just what this thing as efficient as possible.

wireedm · Jan 30, 2014

I just sealed the cap at the top where it mounts to the chimney and around the flue liner sticking up. That'll stop any flow of air. Then stuffed insulation around the liner above the fireplace.

Rudyjr · Jan 30, 2014

The difference in performance of the insert with and without the block off plate can be substantial in some cases depending on the variables of the fireplace. On one friends exterior wall fireplace the performance between with and without was unbelievable. i know that when I installed mine it was very little extra cost and work and I have been satisfied with the performance of my stove from the beginning. I would have never even thought of doing this step it weren't for the good information I was given on this site. Every single installer in my area will tell you that it is not needed and that they don't do it when they install inserts. When you really try to nail them down as to why it is because they either don't want to do the extra work or they are unsure of what is involved.

hamsey · Jan 31, 2014

I installed the plate. Some cursing involved, but it is in. Since I am new to this not sure if it making a difference but I have peace of mind knowing that it is in.

bens_igloo · Jan 31, 2014

Can someone comment on the best type of Roxul insulation to use? They have many different types.

Rudyjr · Jan 31, 2014

What I used was considered Roxul fire stop insulation. I went to a local commercial insulation contractor around the corner from where I work and told them what I was doing, they gave me a piece.

tickbitty · Feb 1, 2014

rwhite said:
I did mine in 2 pieces. The back of my fireplace was almost identical to yours. Will the bricks on either side of the 2 missing ones come out? I removed the entire run of brick and just rested the plate on top of those in the back of the firebox. I used a bit of adhesive that came with the liner to hold the insulation to the plate. Then I slid it into the firebox and rested on the back shelf and used self tapping screw to screw it to the lintel in front.

Good idea, I had not really considered that, but will have a look. In any case I guess I"ll be waiting till the end of the season but thank you for the ideas.
Anybody have any thoughts on the idea of using the thick kaowool pad, or whether that stuff is more dangerous?

Rudyjr · Feb 1, 2014

tickbitty said:
Good idea, I had not really considered that, but will have a look. In any case I guess I"ll be waiting till the end of the season but thank you for the ideas.
Anybody have any thoughts on the idea of using the thick kaowool pad, or whether that stuff is more dangerous?

Seems to me that someone mentioned Kaowool being nasty stuff to work with from an airbourne fiber perspective, not positive.

Blockoff plate vs insulation only blockoff...

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