New Block Off Plate and Insulation for Jotul

So after a lot of aggravation and some harsh words with the dealer they finally showed up this afternoon and pulled my insert. After they left I started tightening up my firebox.

Once it was out I could see that although the installer was originally supposed to have insulated the damper area w/ Roxul there was very little there. He must have done a decent job up top because I get no drafts outside the liner but I added about 4 bats worth of Roxul up to about 4' above the damper, all in the smoke shelf (a lot of dead volume up there) and then above and below the damper.

Then I added a 24 ga block plate and added another layer of Roxul. This should make a bigger difference than I thought it was going to since the damper area was not nearly as well insulated as I believed it was. There was only two small pieces sitting along side the liner with open space all around. It was as good as having nothing.

It supposed to go back in on Sunday. Cross my fingers.

Ansky said:

Enjoy the benefits!

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Did you run w/o a plate first then add one? Curious what to expect as far as stove top temps.

I dropped and did final fitting of my block off plate. Added one last layer of Roxul above the plate too. I layered the base with 3 pc of Durock to raise and level the unit. Lastly I have almost no room for insulation on the back, none at all for the sides and I don't want to block the air intake. So I split a piece of Roxul to about 1 3/4" and then used some metal to hold it in place. This should insulate the area where the secondary air enters the stove and the back corners which I've felt tended to be cool sections.

The stove goes back in tomorrow. Hope it's worth the effort.

Colorado Boy said:

Just curious how much one package of Roxol will do. I am wanting to insulate above the block off plate and below the top cap on the roof around the liner. Thanks

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I bought one pkg of the Safe and Sound. Used about half and was liberal with it. If I had the room I had enough to easily do the firebox too so one should be enough for an avg application.

So the 550 is back in her home safe and sound. The installers came back this AM. I was able to get a nice bead of high temp silicone around the edge of the block off plate and stuff the gap between the plate and the draw down adapter with Roxul.

During the first install they put the stove in place then tried to seal the gap between the liner and the draw down but they had a tough time because it's a tight space. This time I told them to do it first so much better seal was achieved this time around. I know it may not even be needed but I could feel air so I feel better about it.

The installer also added additional Roxul up top before resealing the top plate.

I doubt the liner at the top plateI gets very warm so that silicone is probably fine but I guess I'll give the silicone I used in the firebox time to cure before I fire up. Seems to dry to the touch quick.

Just as a follow up I had two small fires this afternoon and eve which was good since the silicone instructions call for that to cure the product and it wasn't too cold so worked out fine.

The first thing I notice is that the top temp is not very different so far but the air that comes out is a lot hotter. I think that's because the top shroud now has the plate right above it so the air is being heated by the top and the shroud. See more o ce I burn bigger hotter fires when it gets cold again.

I thought I would update my experience now that I've had a few weeks with the new setup. First off prior to the block off the stove top temp would easily rise to 650 or more, even with relatively small fires but would cool quickly compared to now. Even though by all accounts the Jotul can really take the heat It did make me wonder how I could really ever stuff the box full w/o over firing. Now stove temps seem to be more appropriate for the size of the fire. So for example now a mid sized fire will get the top to peak at say 550 and cruise at 450-500.

No longer getting high stove top temps with small fires might sound like a disadvantage but I believe it was because I was heating the stove with the pipe so even though it would get pretty hot peak and cruise temps did not last as long. Also as I have mentioned elsewhere the exterior brick at the level of the smoke chamber (12-18" above stoves top plate) could be as much as 80 F when outside temp was around 30 whereas now it's more like 40 or so. Again this was due to the pipe losing heat. Now that the pipe is retaining heat better I should get less creosote. I'm interested in what my next sweep looks like.

Before if I was at 5 or 6 hundred and turned up the fan the temp would drop. Now the stove holds the temp better and stays hotter longer. So overall although I can't really measure it my impression is that the stove seems to put out more meaningful heat for a longer period of time especially in the coaling stage. Also I feel like draft is improved and that stove is breathing better (pulling primary and secondary air) but there are a lot of variables so again w/o objective measurement it's hard to say for sure.

Heard many folks say that their stoves put out more heat with the surround off. I have the insert set so the surround is 3/4" off the brick which allows some of that trapped heat out. I haven't decided if it would be better to keep that heat trapped or leave it as it is.

Overall I'm comfortable to say that the stove is performing better and able to heat the house better than it was in the colder weather.

woodgeek said:

This is an exterior masonry fireplace? If so, why not line the whole masonry firebox with plenty of Roxul behind the insert? With the surround in place (and pulled out 0.75") it would be invisible.

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If you read post above you see I did not have enough room. The back corners of the insert almost touch the masonry on the sides. Even the layer I was able to put at the back could not be a full thickness batt.

The exterior brick at the level of the firebox where the insert resides never got that warm anyway so the losses there are comparatively less. The smoke chamber and above was a different story.

woodgeek said:

Sorry I missed those details....

I am still wondering why not cover all the brick. I don't follow your logic. Bricks getting warm...there must be loss there. Bricks not getting warm, less loss?? My walls are warm and my windows are cold...

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What do you want me to cover it with? It's not a question of logic it's a question of space.

woodgeek said:

If there's only room for half thickness...ok, a lot better than none. Just not clear why you did half of the area in the back, and not the whole back and sides? I think you answered....no space in those other areas? Brick is a great thermal conductor, so a lot of heat can just go around the batt you put in.

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OK I'll take a few minutes. I researched my options pretty thoroughly here and with one forum member in particular and was given the advice that Roxul alone was not terribly effective, probably as a result of air infiltration (insulation alone does not stop air movement) until a layer that stopped air flow was added such as Durock. Same reason a metal block plate is more effective than insulation alone.

So my plan was to line the entire box with Roxul and cover with Durock. Once I had the insert back out it turned out that that I did not have room to even line the firebox with Durock alone let alone Roxul and Durock.

I considered using Roxul fiber board (which is 1/2" but can be compressed) and a layer of sheet metal to block air flow then literally shove the insert in as far as possible. Ultimately I decided the space was so tight and the cost (time and material) was high enough that it was not worth it. I also had the concern that I could block air flow to the secondary air inlet.

I would rather have followed my original plan because I agree it would have been better and it would have been cheap enough. But as I mentioned when measuring the bricks with an IR thermo at the various levels, those bricks at the area where I was unable to insulate are just a few degrees warmer than those at the outer corners of the chimney so I think my cost benefit assessment was reasonable.

The back of the firebox angles towards the opening so if I had insulated all the way up the back it would have been touching the insert. Insulating the top of inserts seems to be a no no.

The metal plate (which was the primary goal) I added is right at the level of the lintel (there is only about 2 1/2" from the upper heat shield to the block off plate) and the area above the plate is stuffed full with Roxul so the upper area of the firebox is well attended to and was by far the problem area. As I indicated I would have rather have followed my original plan but before and after measurements are favorable so I think it was worth it.

woodgeek said:

Thanks for the explanation.

I think the priority has to be (1) having no airflow to the outside up the stack, around the liner (solved by either a sealed plate at the top OR a sealed metal block-off plate) (2) avoiding a convective (air loop) path between the firebox and the chimney (again outside the liner), solved by insulating the area above the firebox (either above a metal block-off plate, OR without a block-off plate if the top plate is well sealed) and then (3) insulating between the insert convection shell and the masonry firebox.

Looks like you have 1 and 2 covered, and have a partial coverage of (3). I don't buy the advice you were given that some roxul without an airbarrier e.g. metal would have been ineffective. A lot of folks do the roxul and painted sheetmetal and then leave their surrounds off---the metal there is functional and aesthetic. Behind a surround, though a lot of folks just stuff loose roxul all around the shell. So long as you are not blocking the airflow in the shell (or secondary air), insulating outside the shell does not appear to be a problem.

Not trying to open pandora's box here....sounds like you made the best of a tight fit situation.

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Hey, discussion and relating experience is why this forum is so good so let's open that box, I don't mind. Did what I did/could and trying to pass along what I'm seeing. Maybe someone is helped or can do better for themselves.

Not sure the individual who gave the opinion about Roxul would have said Roxul alone was wholly ineffective but the difference with Durock was apparently significant to the point that if given a choice of Durock alone v. Roxul alone, the recommendation was Durock.

A layer of Roxul and a layer of metal to reflect heat and block airflow is probably a highly effective combination. The Jotul has a pretty thick heat shield and the sides of the unit don't seem to get very hot (can't feel the back). I can touch the sides by sticking my fingers behind the surround and almost no appreciable heat is exiting from behind the surround on the sides so I'm inclined to think the Jotul's design is pretty effective at retaining heat in the vent. A fair amount of heat does exit from behind the surround at the top. I think that heat is coming from the 2-3" exposed section of pipe between the flue exit and the block off plate. Maybe I should push it in the rest of the way IDK.

One of the most favorable things is that the pipe is not giving up all it's heat to the brick. As I said previously I was seeing outside brick temps of 80 F in 25-30 weather in the area by the damper/smoke chamber which was a major heat loss. Under similar conditions it's now around 40 F. The block off plate is very low in the setup so that heat is not getting into the room but the chimney should function much better now. Feel like I'm getting better draft during operation and my understanding is that secondary air flow is improved with good draft characteristics.

Ran the Soot Eater up the flue and gave the box and baffles a brushing and sweeping. Thought I would post what I found since this is the first cleaning since I re-did the insulation and added the plate.

My last cleaning was 1/12/14 and usually ended up with a 1/2 coffee can that included a good deal of crunchy/shiny black creosote. Wasn't glaze creosote but had a bit of sheen. The flakes were 2-3 mm.

This sweeping (1/19/15) I got closer to a 1/4 can of fine brown with maybe a little crunchy black but not of the same consistency in that it was smaller and with less of a sheen. By far mostly it was chocolate brown fines. Went on the roof to check the cap and could see where the Soot Eater head had whipped around up there.

There was less "stuff" above the baffles too so all in all much cleaner.

kennyp2339 said:

Nice, is there more heat coming into the room?

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Previously very cold weather impacted performance. Now I no longer have any problems getting the unit hot and running right. Box holds heat better so blows hot longer and flue is not wasting heat to the great outdoors.