Materials used to line fireboxes - a test

[karri0n]

Still very interesting. I badly need to replace several bricks n my IR, and I plan on researching further and following this thread so we can find a good brick with a decent performance:rice ratio.


@Precaud: as to the sketchiness of firebricks.com, I think you are supposed to go there already knowing what you're looking for. The site seems to be for manufacturers.

 

[Peter B.]

I'm also interested in finding insulated firebrick splits... (9" x 4" x 1.25" or 1.0") but don't feel myself knowledgeable enough to evaluate their properties... even if I were to find a source myself. (I'm also on a dialup connection which makes 'dedicated' web searching an agonizingly slow process.)

So, I'm hoping precaud will 'spill' if/when he finds a source...

Please and Thank You.

Peter B.

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[precaud]

Today I did the usual round of three burns, with the Zircar side liners plus the vermiculite bottom in place. Results:

Load 1 : 680 Top...500 Side
Load 2 : 820 Top...520 Side
Load 3 : 780 Top...570 Side

Compare this to the original set with standard cast iron liners:
Load 1 : 550 Top...370 Side
Load 2 : 670 Top...430 Side
Load 3 : 730 Top...450 Side

VERY fast warmup, and almost a 100F average increase in output temps on the top and sides with the same size fuel load and same air settings. Not bad. I've never felt this stove radiate like it now does. It's now in the same league as our fave the old 602. The clean burn pattern on the side liners extends even farther back into the stove and is almost completely free of residuals. Smoke out of the chimney was the cleanest I've seen out of this thing. The 2ndary flames on the second and third loads were like nothing I've ever seen on this thing. (Too bad you have to lay on the floor to see it...) All three loads left no unburned wood in the back - the raised internal temps appear to be enough to gassify the whole load now. This stove is now performing as I thought it would when I bought it, and is no longer an underperformer.

All this from better insulating the firebox and taking 21+ lbs of mass out of the lining. I hope this demonstrates clearly that the whole concept of using mass to "hold the heat" inside a firebox is a bad idea. To hold it, you must take it from where it's really needed. Low mass and high insulation is where it's at.

I think that's about as far as I can go with the F602 stove, except maybe adding some leakage air at the bottom rear and a few air holes at the very back of the secondary manifold. I wish I had something that uses standard firebrick splits to play with. (The Quad does, but it's lining is already excellent.) I'll continue to look for 1.25" IFB's but someone else will have to try them out. Meanwhile, I'm keeping an eye out for 1" ceramic material to replace the Skamol on the sides of the Nestor Martin.

 

[Jimbob]

Very interesting. It seems to support the argument that the light firebrick would work better than the heavy, dense stuff. I't not exactly what you were testing but sort of along the same lines.

 

[begreen]

Good data and nice results. To summarize so far:

Zircar refractory liners only
Load 1 : 650 Top...440 Side
Load 2 : 750 Top...500 Side
Load 3 : 770 Top...510 Side

Zircar liners and vermiculite bottom liners
Load 1 : 680 Top...500 Side
Load 2 : 820 Top...520 Side
Load 3 : 780 Top...570 Side

Original set of standard cast iron liners
Load 1 : 550 Top...370 Side
Load 2 : 670 Top...430 Side
Load 3 : 730 Top...450 Side

How would you rate the durability of the vermiculite bottom liners? Weak, moderate, strong? For cost reduction have you considered casting with any of the refractory mixes that the VC owners have been experimenting with to cast their own combustion boxes? It would be pretty easy to make your own forms for standard brick sizes.

 

[precaud]

Very interesting. It seems to support the argument that the light firebrick would work better than the heavy, dense stuff. I't not exactly what you were testing but sort of along the same lines.

Jimbob, it does very much support that argument. The iron/ceramic wool sandwich is likely the worst case, but the heavy colored firebrick would be next to it at the bottom of the list.

 

[precaud]

How would you rate the durability of the vermiculite bottom liners? Weak, moderate, strong?

It appears to harden to a more brick-like consistency after being fired a few times. Based on the Skamolex in the Nestor Martin, used on the sides and bottom, I'd say it's very strong. (The slabs I used are from Skamol.)

For cost reduction have you considered casting with any of the refractory mixes that the VC owners have been experimenting with to cast their own combustion boxes? It would be pretty easy to make your own forms for standard brick sizes.

For unusual shapes/sizes, it might be a good idea, I'd have to look into the material properties. It's so much easier to work with readily available material of the right thickness, if it can be found...

It also would have been nice to have a few more sensors, capture the output with a data logger at regular intervals, and plot the sequence of burns so one can better see the area under the curve. I have the logger but not the thermocouples...

 

[kenny chaos]

It would be interesting to know the fluctuations in the flue temps during each firing cycle. Those can be very telling.
It'd also be interesting to know the variations in burn times. Maybe by reducing mass, you will be reducing time of total burn (soapstone affect).
It sounds like you're convinced of your resluts and I applaud your time, effort, and sharing, on this project.

 

[karri0n]

Precaud, what is the difference in the R value of the vermiculite and the zircar liners? I'm wondering if vermiculite might be a possible low cost alternative to the zircar for the lining.

 

[jebatty]

The vermiculite slab, since it cuts so easily, would it make sense to install it behind the firebrick lining? Would reduce the size of the firebox but would add the heat resistance value.

 

[precaud]

Precaud, what is the difference in the R value of the vermiculite and the zircar liners?

The thermal coefficient (Tc) of these materials (K) at 1000º are (lower numbers are better insulators):
Skamol V-1100 Vermiculite slab : 1.10
Zircar RS-1200 : 0.66

These numbers are per inch of thickness, so you multiply it by (1/thickness in inches). So 1/2" RS-1200 is 0.66 x 2 = 1.32, and 1" vermiculite is 1.10 ( I have never seen any Skamolex other than 1" thick).

This Tc rates the material's convective (i.e. air-coupled) resistance to heat transmission. The basic test has two chambers at equal temperature with a piece of the material being tested in between. One chamber's temp is raised by X amount, and the time it takes for the other chamber to rise by Y degrees is measured. That's basically how the Tc is calculated.

Compared to a woodstove firebox, what is missing from this test? Radiant heat. The heat source is outside the chambers and piped in. A large amount of the heat in a firebox is radiant, from the flames and the hot coals. The darker the color of the liner, the more it will absorb the radiant heat. It is no accident that the best insulators are white or nearly so. And that requirement dictates the materials that can be used to make it. Materials that are either white or colorless and can withstand high temps are expensive.

I'm wondering if vermiculite might be a possible low cost alternative to the zircar for the lining.

Sure, especially on the bottom, where it's color would be buried in ash so it won't absorb the radiant heat. For the sidewalls, it's not as good as a good lightweight firebrick.

But it's important to say again... which material you choose is going to be largely dictated by the thickness of the liner you're replacing.

 

[precaud]

The vermiculite slab, since it cuts so easily, would it make sense to install it behind the firebrick lining? Would reduce the size of the firebox but would add the heat resistance value.

See previous post. Sure, it adds insulation, but it adds weight too. You want high insulation AND low mass.

 

[precaud]

These guys sell vermiculite slab in 1" and 1.5" thickness:
(broken link removed to http://www.euclids.com/kilnbuild&repair;.htm)

I'm still looking for a good source for IFB splits in the 60-70 lb. density range. All the 1.25" bricks I've found so far are not the insulating type.

There is a seller on eBay that has 2800º 65 lb. density IFB in 2" and 2.5" thicknesses, made by Thermal Ceramics, 30 bucks for a box of 15, and has lots of it available. That's a super price, but you'd have to cut it down to the desired thickness with a tablesaw or handsaw. I got the spec sheet on the stuff, and it's better material than any stove mfr is putting in their stoves right now, and would hold up as well as or better than the stuff PE and Quad are using.
http://cgi.ebay.com/Firebrick-kiln-ceramic-oven-15-pr-bx-Morgan-K-28-silica_W0QQitemZ290263097610

 

[kenny chaos]

Being a typical guy, I also waste too much time trying to invent a better mouse trap but it is fun to tinker.

 

[precaud]

whadya mean, "also" ? Speak for yourself.

 

[precaud]

Here are a couple interesting articles with tests of insulation materials for wood cook stoves, which are commonly used in poor countries around the world.
http://www.hedon.info/InsulativeCeramicsForImprovedCookingStoves
(broken link removed to http://www.repp.org/discussiongroups/resources/stoves/Andreatta/Heatloss.htm)

Though his numbers for thermal conductivity are lower than others I've seen for the same materials, his vermiculite and pumice brick formulations performed quite well in these tests. Pumice brick, which many believe is used in PE and Quad stoves, has very high insulation properties, on a level with K23 insulating firebrick. Density is around 50 lbs/cu ft., about the same as K23 bricks. I haven't found any specs on crush strength (an indicator of ruggedness) but it must be higher than the K23 which are quite soft and crumbly. Home Depot sells pumice brick pavers in several sizes if anyone wants to experiment with them. Masonry blades for a table saw are just a few bucks, and would probably be best for slicing them down to desired thickness.

Also interesting is their finding of the superiority of the low mass/high insulation firebox combination for clean combustion AND highest heat transfer.

 

[karri0n]

How does castable refractory match up with the thermal properties of the other materials listed?

 

[precaud]

Good question, I don't know the answer. Also there are many types of castable.

 

[johnn]

Precaud: Your thoughts on K28, thermal ceramics,45%alumina,52%silicia, 1% ferric oxide. Better than K23`s??? MY mind keeps telling me whenever I read.,(...the brick used in kiln manufacturing...) that a kiln wants a brick which holds ,,rather than transfers heat,,. Does my mind have a mental block ,
or are these the type I want??
Regarding the installation of a BAFFLE: Between the secondary tubes,baffle,1"insulation blankett, a lot of cu.ft gets consumed> Your thoughts on a free 1/2 in. stainless baffle coated with itc100 ceramic coating, to minimize cu.ft. reduction by not using the 1" insulation blanket. I think cost would equal out and leave more space. I`ve read all threads numerous times along with each added text and find myself still confused at times, not being able to understand the charts,,,I have been trying!!
would cutting brick thickness down to 1" be acceptible?? IT seems that the "whitest " "or""( absense of color) in a brick are manufactured in either India or China. Not exclusive of course,,its just when I find a new link,,,its far away, and again I cant decifer the test charts. Thanks

 

[precaud]

Hey ml, good questions.

Precaud: Your thoughts on K28, thermal ceramics,45%alumina,52%silicia, 1% ferric oxide. Better than K23`s???

If you're referring to these:
http://cgi.ebay.com/Firebrick-kiln-ceramic-oven-15-pr-bx-Morgan-K-28-silica_W0QQitemZ290263097610

I have the specs on them. The 51 pcf density is pretty much equal to the pumice bricks. Crush strength is higher than the K23, so my guess is they are pretty much on a par with the pumice bricks in their handling of abrasion and bumps. They have better radiant reflection due to their whiter color. I may order a box of them this week. The price can't be beat.

MY mind keeps telling me whenever I read.,(...the brick used in kiln manufacturing...) that a kiln wants a brick which holds ,,rather than transfers heat,,. Does my mind have a mental block, or are these the type I want??

Yes, they are the type you want. And yes, it's a mental block, caused by the use of the word "hold." Why do you want to hold heat in the lining? What for? You don't want to hold it, you want to stop it from escaping so that the interior space stays hotter. You have to separate in your mind:
1. the physical kiln from the space inside it. And for a woodstove,
2. Keeping the combustion environment hot from getting the heat out (the heat exchanger.)

If you try to do both in the same space you'll do neither very well.

Imagine this: you're in a one-room house with steel walls. You're putting heat into it, and you want to get the temps as high as possible inside the house. To achieve this, what treatment would you apply to the inside of the steel walls: line them with 2.5" of heavy brick, or spray 2.5" of lightweight foam insulation? The brick will store heat and even out the temperature fluctuations in the room. But that isn't the goal. The insulation will be MUCH better at stopping the loss of heat and making the inside temperatures higher.

You don't want even heat over time inside the firebox; you want it as hot as possible while flames exist in it.

Regarding the installation of a BAFFLE: Between the secondary tubes,baffle,1"insulation blankett, a lot of cu.ft gets consumed> Your thoughts on a free 1/2 in. stainless baffle coated with itc100 ceramic coating, to minimize cu.ft. reduction by not using the 1" insulation blanket. I think cost would equal out and leave more space.

Interesting idea. But how about a 1/2" ceramic fiber board? It weighs alot less than the stainless baffle and is a better insulator.

would cutting brick thickness down to 1" be acceptible??

I'm thinking of the doing same thing, to replace 1" of vermiculite. As long as it's dense enough to hold up, I don't see why not.

IT seems that the "whitest " "or""( absense of color) in a brick are manufactured in either India or China. Not exclusive of course,,its just when I find a new link,,,its far away, and again I cant decifer the test charts. Thanks

Yeah, the dust created is nasty stuff... inside-the-factory health regs are probably looser over there... make sure you wear a mask if you cut bricks down.

 

[johnn]

Precaud: Thanks for your reply. In regards to the 1/2 in. ceramic board,,, would a coating still be worth trying to increase the temps near 2ndary reaction,,assuming the exhaust would create addequate stove top temps as it exits. That stuff really reflects heat, but life use is unknown. There is a much cheaper coating than the itc 100.
Regarding cutting bricks: I remember years ago while cutting a concrete path with masonry blade,,,my step son shows up hollering about my not using a mask,,,claiming that the process of cutting was creating glass at the point of contact. I`ve worn masks since then, but would like to note: Reading the articles about poorer countries making brick,,and the natural fillers used which burn away at firing ect.ect...These pores playing a large roll in the design and function, it may be worth noting that a fibre cutting disk leaves the cut surface of a paver brick quite smooth, almost glossy. Just saying that,a diamond blade along with the use of water to combat heat and wear (those such as masons use) may be in order. I`d just hate to disrupt the pores by glazing them shut???

 

[precaud]

Precaud: Thanks for your reply. In regards to the 1/2 in. ceramic board,,, would a coating still be worth trying to increase the temps near 2ndary reaction,,assuming the exhaust would create addequate stove top temps as it exits. That stuff really reflects heat, but life use is unknown. There is a much cheaper coating than the itc 100.

ml, I haven't experimented with it, but I have my doubts about the effectiveness of coatings in a wood stove. It's not as if that stuff has magic insulative properties; best I can tell, it's a radiant barrier. But it's worth a try to see if it helps or not.

Regarding cutting bricks: I remember years ago while cutting a concrete path with masonry blade,,,my step son shows up hollering about my not using a mask,,,claiming that the process of cutting was creating glass at the point of contact. I`ve worn masks since then, but would like to note: Reading the articles about poorer countries making brick,,and the natural fillers used which burn away at firing ect.ect...These pores playing a large roll in the design and function, it may be worth noting that a fibre cutting disk leaves the cut surface of a paver brick quite smooth, almost glossy. Just saying that,a diamond blade along with the use of water to combat heat and wear (those such as masons use) may be in order. I`d just hate to disrupt the pores by glazing them shut???

A smooth, glossy surface will be better, it's more reflective. The pores that matter are the ones inside, not on the surface.

 

[precaud]

Since temps are on the rise around here, since the X33 needs a new door glass gasket (already...), and since a tendon tear is stopping me from doing more interesting things, last weekend I decided to put the modded F602 back in and live with it for a while. But before doing so, I decided to address the problem of no air (hence no combustion) in the back half of the stove. I drilled five holes in the secondary manifold in the very back of the stove, see the photo for locations. The yellow dots mark where the holes were drilled, 1/8" for the upper four and 7/32" for the bottom one.

The results are very good. As expected, there is now combustion in the back. No more unburned chunks to rake forward. The "clean burn zone" (the area that burns clean on the side plates), extends another couple inches toward the rear. (One has to wonder why Jotul didn't put these holes there in the first place; every other EPA stove has 2ndary air back there. I'd bet it was a marketing decision - heaven forbid the little F602 outperform the F100...)

If I could do the holes over again, I'd do say six 1/16" holes above and one 3/16" below.

Everyone loved the pre-EPA 602 because it put out an amazing amount of heat from such a small box. The F602 came along with great fanfare but clearly underperformed its predecessor. But with these mods, this stove is now on a par with the old 602. It heats up as quickly, burns as hot, burns through each load reliably, and doesn't build up coals as quickly. So if you can pick up a used one for cheap (I've seen them for 300-350 around here,) it's probably worth doing these insulation and air mods and have yourself one nice little heater.

 

[ernie]

Interesting, I have been thinking of replacing my firebrick in my Quad 7100 Fireplace with Skamol liners. What do you think about that? I think it might burn hotter and keep the glass cleaner.

Ernie

 

[precaud]

I think it might burn hotter and keep the glass cleaner.

More likely the opposite. 1" thick Skamol is a poorer insulator and weighs more than the 1.25" pumice bricks. That's not what you want. I think the only step up would be the K28 firebricks mentioned above. But you'd have to slice them in half to get the right thickness, easily done with a masonry blade on a table saw. But it's a dirty job. The dust is nasty stuff.

With the Quads, dirty glass isn't caused by low firebox temps, but by the design of the primary air system. The air feed is asymmetrical and weak at the edges. Despite that, they're one of the most efficient stoves out there.