ceramic vs steel baffle

My Jotul Oslo has a vermiculite baffle with about a half inch of rockwool insulation laying on top. They used to come with cast iron baffles, but the company says they moved to vermiculite due to a problem with the cast iron warping in the Oslo.

I just saw a Jotul F600 on the showroom at the local dealer and it had a CAST IRON baffle. So, maybe people run the smaller F500 Oslo hotter, thus the warping. Who knows eh?

My baffle is cracked right now, I have another ready to put in but will wait until summer to do so.

My Morso has a 2 piece cast iron baffle with insulation on the top.

The two pieces pop, ping, and move a bit when the stove gets up to temp.

I have always wondered this myself; seems to me like a thermal-mass issue, as well as a thermal-insulation issue.

Is it better to have a "heavy" baffle that will hold some heat and help with re-ignition of the secondary burn after a reload, or is it better to have a light baffle that can cool off, but then gets up to temperature quickly?

I would guess you could only really get insight into something this subtle by having two stoves side-by-side, burning under identical conditions and with identical fuel... i.e. the kind of thing manufacturers do in their labs.

All that said, I myself would favor either stainless or firebrick, but for practical reasons rather than performance reasons... durable in the first case, cheap to replace in the second. The various refractory boards ("high-temperature drywall") seem too fragile, and cast iron can/does crack.

I insulated my Jotul 8's cast iron baffle with ceramic wool, but have to admit I'm now kind of just waiting for it to crack. $150 part. Will probably try to add a stainless baffle in front of it when it does crack, though that will cut into firebox volume a fair amount.


Eddy

p.s. if anyone *really* wants to impress their friends, Titanium would seemingly make just about the ideal woodstove baffle... low thermal conductivity, light weight (low thermal mass), and just about impervious to ordinary flame combustion temperatures. Just take out that 2nd mortgage to pay for it!

I have just replaced the baffles on my Napolean 1900 with dura rock slabs. I think the origonal baffles where made of vermiculite but can not tell. Does anyone have any idea how well these new dura rock slabs should perform or how they may effect the stove over time. The reason I used dura rock slabs is that I have a lot of it around the house and its very inexpensive compared to buying new baffles from the manufacturer.

Durock ? You mean like tile backer board? I thought that the durock would just crumble under the heat. Very interesting if it works since in a pinch, we all could pick up a piece at the local hardware store.

ansehnlich1 said:

My Jotul Oslo has a vermiculite baffle with about a half inch of rockwool insulation laying on top. They used to come with cast iron baffles, but the company says they moved to vermiculite due to a problem with the cast iron warping in the Oslo.

Click to expand...

Ha! My baffle warped last season, one year out of warranty. I just noticed it one day. the right baffle (there are 2, as I'm sure you know) is "curling" up on the left side. It's not real bad so I'm still burning it that way, but I wondered exactly what I did to cause it.

How much for the replacement vermiculite baffle? I priced a replacement cast iron one at about $50.

Highbeam said:

Durock ? You mean like tile backer board? I thought that the durock would just crumble under the heat. Very interesting if it works since in a pinch, we all could pick up a piece at the local hardware store.

Click to expand...

I think BeGreen corrected me a while ago on the name of the substance I am using. In this post:

https://www.hearth.com/econtent/index.php/forums/viewthread/9392/P22/

I think he correctly identified it as Durock.

So now the stove has been in a high, hot burn for about 4 hours since putting in the new Durock baffles.

It seems to be working well. It will be a while befor I start noticing any difference in the burn efficiency or effects on the stove.


There is a picture of the stuff at this location:

https://www.hearth.com/econtent/index.php/forums/viewthread/9392/P0/

Scroll down the page untill you see the first picture of a Napoleon 1900 stove on a tile floor.

It would be interesting to know what the thermal characteristics of ideal baffle material should be and and how close to Durock comes to meeting those specifications. All I know if Durock is that if you put a blow torch on one side of it, for many minutes, you can still touch the other side without burning your fingers. So sure its very thermally insulative.

Hi again,

I did some research on the thermal properties of Vermiculite vs Durock and found that the thermal conductivity of Vermiculite can be found on this table and is 0.058 W/mk
http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html

The thermal conductivity of Durock can be found at this site and is 0.040W/mk:
http://www.rockwool.hr/graphics/RW-HR/Tehnicki listovi/DUROCK-C/Tehnicki list DUROCK-C ENG.pdf


1 W/(mK) = 1 W/(moC) = 0.85984 kcal/(hr moC) = 0.5779 Btu/(ft hr oF)

So it looks like Durock is a better insulator than Vermiculite.

BTW, the thermal conductivity of copper is 401W/mk

Durock is far more durable than my old Vermiculite baffles.

I almost scored some Gemcolite. I inquired looking to not have to get ***** on ceramic fiber baffles from the manufacturer. The guy as ready to see how they performed in my brand of stove but someone else at the plant shut him down. Anyhow he recommended the material withstand 2600F. He said he would not use the 2300F as a stove baffle.

http://www.rsifibre.com/fiberboard2600.html

Durock MSDS

http://www.usg.com/USG_Marketing_Co...nts/MSDS/Drck_CementBoard-MSDS_14-090-001.pdf

Performance

What is the maximum temperature that DUROCK® Brand Cement Board can handle?

DUROCK Brand Cement Board can withstand temperatures of up to 175 degrees F.

Does not look like a good choice for Baffle Material.

Good catch. So far the ones I have installed have lasted all night without any signs of wear. They are as clean and "new" as when I put them in. That is there is no soot on them at all.

HeatsTwice said:

Good catch. So far the ones I have installed have lasted all night without any signs of wear. They are as clean and "new" as when I put them in. That is there is no soot on them at all.

Click to expand...

If you take them out, do they appear brittle? It's always hard to tell what is meant by "withstand temperatures to X". That could mean for it to still function in it's intended purpose. Just like it can only withstand 100 freeze thaw cycles.

I'd be very careful. Should they fail you may encounter a runaway fire. My baffles only leave a one inch wide opening at the glass to allow exit out the flue. Without them, that opening increases by a factor of 36 for me.


Now I wonder how they would perform wrapped in fiber blanket.

carp said:

HeatsTwice said:

Good catch. So far the ones I have installed have lasted all night without any signs of wear. They are as clean and "new" as when I put them in. That is there is no soot on them at all.

Click to expand...

If you take them out, do they appear brittle? It's always hard to tell what is meant by "withstand temperatures to X". That could mean for it to still function in it's intended purpose. Just like it can only withstand 100 freeze thaw cycles.

I'd be very careful. Should they fail you may encounter a runaway fire. My baffles only leave a one inch wide opening at the glass to allow exit out the flue. Without them, that opening increases by a factor of 36 for me.


Now I wonder how they would perform wrapped in fiber blanket.

Click to expand...

I havn't taken them out since they are well over 500 degrees right now. But I have poked them with a fire iron and the "sound" (thud) they make is the same as before I put them in.

BTW, I agree with your comment on the intended use. I am using Durarock for something it was not intended to be used for. But it "seems" to be working. That is, the temperature is well over 175 degrees, the baffles are still there, in one peice, clean, there is no smoke comming out of the chimney and the fire is burning down to the usual bed of coals without any unusual other type of activity occuring (yet).

When I empty the ashes next time (and the stove has cooled off) I will inspect the baffles and report my findings.

did the baffles on your 1900p break ? If so, how long have you had the stove ?

They are fragile to begin with but after 10-12 cords they do get banged up (two years after purchase). The sell for $65 from the manufacturer. They still can be used but I felt I would try out this Durarock idea.

I usually use a couple pieces of firebrick as a simple "grate" to keep my fire up off the firebox floor and allow some air circulation under. This year I didn't have any firebrick handy but I did have some concrete brick, kind of like cinderblock but brick-shaped, so I tried that. It worked fine (not that it's a difficult job) for a couple months, then developed cracks and gradually fell to pieces.

The lesson I drew was that there's a reason why firebrick exists, and there's jobs that ordinary concrete can't do despite its seeming inertness.

Eddy

HeatsTwice said:

They are fragile to begin with but after 10-12 cords they do get banged up (two years after purchase). The sell for $65 from the manufacturer. They still can be used but I felt I would try out this Durarock idea.

Click to expand...

you have burned 10-12 cords of wood in 2 years, in your napolean ? Seems like alot , ecspecially in California.

do you ever have any smoke enter your house from your stove, if its windy outside ?

rumme said:

HeatsTwice said:

They are fragile to begin with but after 10-12 cords they do get banged up (two years after purchase). The sell for $65 from the manufacturer. They still can be used but I felt I would try out this Durarock idea.

Click to expand...

you have burned 10-12 cords of wood in 2 years, in your napolean ? Seems like alot , ecspecially in California.

do you ever have any smoke enter your house from your stove, if its windy outside ?

Click to expand...

I am in Northern California where it usually hovers in the mid 30's durrin the night and 50's durring the day. I also work from home so I run the thing 24/7 from Nov 1st to March 15th (about). My house is 4000 sq feet and I have 2 daughters and one wife (girls = big heat sinks)

My chimney is 16 foot and I never get any smoke ever. I love the stove. There are pictures of it at the URL I posted earlier. This baffle thing is just an experiment. But I have to say the vermiculite baffles the stove came with can't be "magical". Its simple thermodynamic that describes a good baffle. So far, I can prove that durorock has a lower thermal conductivity. At least that is what I see in the charts I've looked at. Also I have not been able to find where it says that 170 degrees F is the max temp it should be exposed to.

My Endeavor uses a combination of steel supports and fire brick. I'm curious to see how well they hold up over time. That's a lot of constant heat, so I'm not expecting any miracles. But of course the tight wad in me is hoping for the best! ;-)

Pagey said:

My Endeavor uses a combination of steel supports and fire brick. I'm curious to see how well they hold up over time. That's a lot of constant heat, so I'm not expecting any miracles. But of course the tight wad in me is hoping for the best! ;-)

Click to expand...

The tight wad in you will appreciate, then, that you can replace every brick in your baffle for like ten bucks. You'll be the envy of every guy with a custom refractory baffle, on that day at least... ;-)

EddyKilowatt said:

Pagey said:

My Endeavor uses a combination of steel supports and fire brick. I'm curious to see how well they hold up over time. That's a lot of constant heat, so I'm not expecting any miracles. But of course the tight wad in me is hoping for the best! ;-)

Click to expand...

The tight wad in you will appreciate, then, that you can replace every brick in your baffle for like ten bucks. You'll be the envy of every guy with a custom refractory baffle, on that day at least... ;-)

Click to expand...

LOL, that's good to know! I wonder how well the steel supports will hold up over time. They look to be harder to replace!

HeatsTwice said:

They are fragile to begin with but after 10-12 cords they do get banged up (two years after purchase). The sell for $65 from the manufacturer. They still can be used but I felt I would try out this Durarock idea.

Click to expand...

I have a 1400 and the baffles are fragile. Touch them with wood while loading or anything else and pieces will come off them or they will gouge. I haven't even put 6 cords through mine in 3 years and they are about toast. You can see where there may have been holes in the mold to cast the baffles. They look like little plugs and are about to fall out making holes.

I will not be spending a single penny on a Napoleon baffle.

Since I have about 65sqft of durock in the garage I may also test it out. My stove cools every day while at work so I can put a durock in just one side and yank it every day to check on it.


The 175 Degree temperature limit I noted for Durock above was directly from the manufactures F.A.Q. for the product.

http://www.usg.com/navigate.do?reso...ils/DUROCK_Brand_Cement_Board.faq.html#N20174

carp said:

HeatsTwice said:

They are fragile to begin with but after 10-12 cords they do get banged up (two years after purchase). The sell for $65 from the manufacturer. They still can be used but I felt I would try out this Durarock idea.

Click to expand...

I have a 1400 and the baffles are fragile. Touch them with wood while loading or anything else and pieces will come off them or they will gouge. I haven't even put 6 cords through mine in 3 years and they are about toast. You can see where there may have been holes in the mold to cast the baffles. They look like little plugs and are about to fall out making holes.

I will not be spending a single penny on a Napoleon baffle.

Since I have about 65sqft of durock in the garage I may also test it out. My stove cools every day while at work so I can put a durock in just one side and yank it every day to check on it.


The 175 Degree temperature limit I noted for Durock above was directly from the manufactures F.A.Q. for the product.

http://www.usg.com/navigate.do?reso...ils/DUROCK_Brand_Cement_Board.faq.html#N20174

Click to expand...

Hi,

I know how you feel. The baffles are very fragile and mine match the description you gave - pretty beat up.

With out a doubt, I think Napolean has done a fine job on my stove and, after exchanging emails with their engineering department on a separate subject I can tell they know what they are doning (or talking about). The stove has been great so far but being of scotish decent, I would always look for a pennyless work around. If Napoleon never got any repeat buisness from me or anyone else because the thing is so well built, their marketing department would have been fired (laid off) because the stove would sell itself. Selling replacement baffles must keep them in bread and butter.

So, now for the status of the Durock after two solid days of burning.

First I should say that I took the trivit off and with my infrared thermometer, measured the temp just below it. As usual (and those who know Napolean will already know this) the temperature was approx 900 degrees. I expect all sorts of yammering from everybody about the safty of this but for two years it has always been this temperature (even with the factory baffles) and others on this site have witnessed this independantly. The top plate of this stove is 1/4 steel. And yes I know that the manual says never run the stove hotter that 500 degrees when measured below the trivet. But this is practically impossible given the size of the fire box and I suppose it was put in the manual as a disclaimer.

So after over two solid days of high burn I let the stove cool and took out one of the Durock baffles. This is what I saw:

1) There was some "twist" warpage like that seen on an airplane propeller but not nearly as severe - maybe an 1/8th of an inch at most.
2) There where cracks here and there which did not compromise the structural integrety but it is conceivable that they could one day connect and crack the baffle in half. But I can see that if it did fail, it would do so in the "short length of the rectangle" direction, not the "long length of the rectangle". This means that if the baffle failed catastrophically it would do so in a way which was no worse than the way the factory baffles already had. That is, my factory baffles have holes knocked in them because they have been banged around from firewood insersion, which let hot air (plasma) escape from the fire box directly into the chamber above. These holes are in the direction of the "short side of the rectangle" and have not failed yet.
3) There is no discoloration on either side of the baffles. That is, they are exactly the same color now as they where when I first put them in. To me this interesting because if they where not burning of all of the soot on them by the intended "post burn" mechanism, they would have shown some discoloration by now.
4) There was no crumbling of the baffle even at the points where one may expect it (corners, edges experiencing the highest heat exposure, etc.).
5) Even though the fire had burned down to a very low level, The baffle was hotter than heck and I began to feel the heat of holding it through the welders gloves I bought at harbor freight and had to put it down very quickly.


I fully expect these baffles to fail in an amount of time which is far less than that of the factory provided baffles. But I can make them in 5 minutes and for about 75 cents.

If requested, I can post some pictures of the tested baffles. For now, at the very least, I would say that in a pinch such baffles are good enough to get you through until the manufacturer ships you new ones.