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regular and light weight firebrick differences

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by skidud, Oct 16, 2012.

  1. oldspark

    oldspark Guest

    Here's some more info-two different uses, you decide whether it makes a difference, there is a reason they use them IMHO.
    "Do not confuse lightweight insulating fire bricks with heavy dense firebricks. Insulating bricks are refractory too and of course withstand very high temperatures range BUT for purpose they have very low thermal conductivity and don’t absorb the heat well at all. [​IMG] Those are intentions for heat insulation. For instance if you used them for building of the hot face in a wood fired oven (for cooking) the oven wouldn’t cook, because it wouldn’t store and hold almost any heat. You can however use these insulating fire bricks on the outer side (of the heavy firebrick walls, vault or under the floor bricks and slab) to prevent the soaked in heat in the chamber’s body mass from escaping and achieving superb results. Meaning well insulated oven which will hold the absorbed heat in its mass, where it should be to cook for long time."

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  2. Huntindog1

    Huntindog1 Minister of Fire

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    The numbers left to right:

    MaterialDensity (kg/m^3) - Specific Heat (J/kg-C) - Thermal Conductivity (W/m-C) - Estimated heat loss(MJ)

    Ordinary Brick 1600 - 840 - 0.7 - 5.7
    Pumice Brick 770 - 835 - 0.107 - 1.5
  3. TMonter

    TMonter Minister of Fire

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    I'm of the opinion you should use the type of brick the stove was designed for. Using a denser more conductive firebrick could lead to reduced performance on some stove designs. At the very least you should try to find firebrick with similar characteristics to the ones currently in your stove.
    oldspark likes this.
  4. Jags

    Jags Moderate Moderator Staff Member

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    Exactly the reason I posted my query above. If the pumice style gives my stove more insulating value for the floor of the stove - which allows for ember protection only....will the denser brick offer the same advantage??? Could replacing the bricks with the wrong type be a clearance to combustibles issue??
    raybonz likes this.
  5. TMonter

    TMonter Minister of Fire

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    It would be an interesting question to ask Quadrafire about. I would guess the type of brick has at least something to do with it.
  6. Huntindog1

    Huntindog1 Minister of Fire

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    I like the idea of maintaining a higher temp in my firebrick lined firebox at the lowest primary air setting of my stove. I can maintain my secondary flame action at a much lower setting.
    I think we all would like to be able to turn our burn tube stoves down like a cat stove can be turn down, we wont be able to go as low as a cat stove but every little bit helps.
  7. bryan

    bryan New Member

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    Ordinary Brick 0.7 W/m-C
    Pumice Brick 0.107 W/m-C

    A 7 fold difference in thermal conductivity seems very substantial assuming the bricks are of equal thickness.
  8. begreen

    begreen Mooderator Staff Member

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    In a smaller stove I think a superior insulator would be even more important, especially when you want to have the largest firebox in the smaller form factor. This is why they are using more exotic insulation in most European stoves.


    PS: I'm still waiting for some links for pumice bricks that are cheaper than regular firebrick. Lots of folks would benefit from these sources. Everywhere I have looked they are about 2x the price.
  9. Huntindog1

    Huntindog1 Minister of Fire

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    If you are having trouble finding cheap insulating pumice fire brick, A while ago I exchanged some emails with John Gulland about the use of Ceramic insulation behind my fire brick.
    He said he had thought about the idea to replace his pumice fire bricks with the more durable ones then use the ceramic 1/4" insulation to get the insulative properties back that he got with the pumice bricks. It took about $30 worth of ceramic insulation to do all of my stove.

    If you get the fire bricks with the high alumina content , the higher reflective properties would reflect the heat radiation back into the fire. Add the insulative properties of the 1/4" 2300 deg ceramic insulation with the added reflective properties of the high alumina content fire brick, should provide a nice little performance boost in the stove especially at your lowest all night burn settings.

    Being that most of the heat from a wood fire and its coals is radiated heat I suspect that firebrick with high reflective properties would do more to keep the heat concentrated at the fire.

    I seen online a report of a study done on the effects of preheated secondary air verses non heated secondary air.

    Secondary air heated to 500 deg provided a 7.7 percent increase in efficiency and secondary air heated to 1000 degrees provide a 23 percent increase in efficiency.

    So this indicates to me that with increases in temp, makes the efficiencies better.

    Lastly I suspect that pumice bricks are required in some stoves to meet their clearance specs to walls and such. If you replace your required pumice bricks with regular fire brick then more heat will radiate out the back and sides rather than the top and front as the stove was designed thus heat your walls close to your stove to a higher level.
  10. Huntindog1

    Huntindog1 Minister of Fire

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    I would like some fire bricks made out of this stuff.
    Looks like you can buy a brush on coating.

    http://www.eaglecoatings.net/video/emmissivity.html

    http://www.axner.com/itc100htceramiccoating.aspx

    http://www.axner.com/what-author-nils-lou-has-to-say.aspx

    http://www.hightemptools.com/itcproducts.html

    ITC-100 forge refractory coating
    Invented by Feriz Delkic, founder of International Technical Ceramics, ITC-100 has been been used by the ceramics industry for over 25 years. This versatile high temperature ceramic coating can be applied to a variety of gas forge materials: ceramic fiber blanket, fiber board, refractory brick and castable refractories. In the blacksmithing and bladesmithing world, those who have used ITC-100 in their forges swear by it's value. Most homemade forges cannot reach forge-welding heat without an application of ITC-100.
    EfficiencyITC-100 increases a forge's fuel efficiency 30 percent by reflecting 98 percent of the forge's infrared radiation.
    SafetyITC-100 protects against respirable silica. Refractory materials like Kaowool begin to break down at 1800 degrees F. releasing a form of respirable silica known as cristobalite. When applied to fiber blanket and cured, ITC-100 eliminates this problem.
    Durabilty ITC-100 coats the ceramic fiber blanket forming a protective shell in the forge interior,greatly extending the life of the insulation.
  11. precaud

    precaud Minister of Fire

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    I was intrigued by these coatings as well, but decided against experimenting with them. Here's why.

    They all claim to work by reflecting infrared (that is wavelengths longer than our visible spectrum). Look at them and you'll see they are all white in color, or nearly so. Their reflectivity is largely dependent on their color. If they were black, they would absorb visible and infrared. Inside the kilns in which they were designed to operate, they stay white, unless an accident happens.

    But woodstoves are different. During the warmup stages of a fire, the stove interior (firebrick included) is covered with carbon and soot, and they stay that way until the adjacent area is hot enough to burn them clean. So during the stage of the fire when you really want the coating's reflectivity to be working to help the firebox come up to operating temp quickly, it is covered with carbon and no help at all. (Remember, for an EPA stove, the majority of the emissions occur at the beginning and end of the burn cycle.)

    So I decided that coatings wouldn't be effective in a stove.
    Huntindog1 likes this.
  12. precaud

    precaud Minister of Fire

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    I understand how you're concluding this, concentrating on the radiated energy. My experiments support the efficiency conclusion but the rest didn't work out that way. Increased insulation raises the temps in the firebox, with two consequences:
    1. Increased firebox temps = hotter bricks = more heat conducted into the stove body = hotter stove surface temps = more heat into the room during the flaming part of the cycle. (Higher mass firebrick will lessen this gain by storing more of this heat. Not a good idea.)
    2. Increased firebox temps = the wood in it gassifies at a quicker rate. This definitely can change the way a stove burns. I can imagine in some cases it being harder to control the burn rate. It can also help a stove to burn a load more completely all the way to the back of the firebox. The Jotul F602 definitely benefited from this.

    So if lower numbers for clearance specs on a radiant stove is what you want, use refractory firebrick.
  13. Huntindog1

    Huntindog1 Minister of Fire

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    After putting in the ceramic insulation I have noticed the ash left is lighter and fluffier maybe an indication of a more complete burn.
  14. BrotherBart

    BrotherBart Hearth.com LLC Mid-Atlantic Division Staff Member

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    If you ship 50,000+ stoves a year and have to pay the freight, try to get that sucker EPA certified with the lightest bricks you can find. And be the only place to buy replacements. >> Kinda like Quadrafire with those with the holes drilled in them in the back.
  15. Huntindog1

    Huntindog1 Minister of Fire

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    I thought I read someplace about a coating and it still working once it became dirty, Its called Super Therm.

    Reflective Coating vs. Fiberglass vs. SUPERTHERM ®
    Manufacturers in the past have marketed "reflective" coatings by making claims that they continuously repel heat, and have specific "R" values. The problem with such claims is that these coatings only reflect visual light or short wave radiation, and when they become dirty they stop working completely. Once these claims proved false, all similar coatings were put into the same category and deemed non-viable.
    SUPERTHERM ® was designed and developed with the assistance of NASA, a fact that can be substantiated. The "ceramic compound" blends found to work the best, and are now used in SUPERTHERM ®, resulted from 18 years of testing and research. The difference between the technology of "reflective" coatings of the past and SUPERTHERM ® today, is outlined below.
    SUPERTHERM ® has the ability to block all the different radiation waves. SUPERTHERM ® not only blocks these waves when first applied, but continues to block them after the coating becomes dirty, which happens to all coatings. The ceramics used in SUPERTHERM ® were chosen from over 3,200 compounds, which were studied and tested in order to prove that they would block the different radiation waves the most effectively, producing the following results:
    1. SUPERTHERM ® blocks 99% of UV heat
    2. SUPERTHERM ® blocks 92% of Visual Light (short wave) heat
    3. SUPERTHERM ® blocks 99% of Infrared (long wave) heat
    This results in an average of over 96% of heat load blocked!
  16. rideau

    rideau Minister of Fire

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    To add to Jags pondering, if there really is a significant difference in the insulative values of the different bricks, wouldn't the choice of bricks then affect necessary clearances? That doesn't seem to be the case....at least I've never heard of a MFG who cautioned against changing type of firebrick? Again, asking. I don't know.
  17. rideau

    rideau Minister of Fire

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    Where is Supertherm used? An any standard firebricks?
  18. ScotO

    ScotO Guest

    I'm confused, fellas. Isn't the whole point of having a woodstove in your home to put out heat? I understand you want some reflectivity back into the stove to aid the secondaries and give you a good clean burn, but I want lots of heat out of the stove. I installed regular firebrick in my Napoleon 1900 after burning out all the pumice brick, and it still has a very clean burn and great secondaries.....not to mention it stays hotter for longer periods of time.......Not bashing anyones scientific research, just trying to figure out why you want the majority of the heat in the stove, when I thought the point of efficiency was to get the majority of the heat OUT of the stove....
  19. begreen

    begreen Mooderator Staff Member

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    That's a subjective observation. The stove mfg. needs quantifiable and repeatable emissions reductions that are verified by a certified testing lab.
    Huntindog1 likes this.
  20. nate379

    nate379 Guest

    I have a mix in my stove. I had to replace 7 or 8 bricks this summer when I cleaned it. (they were broken or broke when removing them!)

    The replacements where the lightweight ones. Was all the stove place had.
  21. charly

    charly Guest

    The Esse uses the light weight bricks and it states not to use the heavy bricks as the light weight bricks reflect the heat back into the firebox. For what it's worth. Woody talks about the firebrick. Sorry volume is low on the video. If you have speakers turn them up.

  22. Huntindog1

    Huntindog1 Minister of Fire

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    I just like making people do the "What If Double Check" instead of the "Discount Double Check"

    I think in these newer type stoves most the heat comes out the top and front. as they are lined with firebrick to insulate the fire box. What we are talking about here Is just taking it a little further and using an insulated brick instead of a not so insulated brick, they all are insulated. Its like going to Lowes and looking for the better R-Value in Fiber Glass insulation. With bricks there is a trade off in durablility. But I wanted to point out that in wood stoves there is more to insulative value due to the radiant heat that is the majority of the heat that a stove puts out. As its the radiant heat that allows the reflection factor to be a big factor in wood stoves. All bricks radiate heat back into the fire box just some can do it better. The ones with higher alumina content.

    I also want to point out again even tho some may not agree, that if you can more easily maintain firebox temps , you then can more easily get your stove operating nicely at its lowest setting as most of the time I am working with my stove to get it set to its lowest setting that I can get but still maintain secondary burn. I already have the ceramic insulation in my stove behind the fire brick , instead of insulated fire brick, and the results are noticeable and I like the $30 tweak I made.

    Too make this simple, in these secondaries type stove we all know from experience its all about the heat. We all know if you cant get the heat up in the stove , the stove doesnt perform as well, if you leave the door cracked it wont heat up for you. If your draft is too strong people have experience not being able to get the stove as hot as they would like, putting a manual draft damper in and slightly reducing draft mysteriously allows the stove to heat up a little more. Its all about the heat. Its the extra high heat in the fire box in these type stoves that allows the stove to burn more efficiently. 60 percent or more of the heat in wood is in the smoke gases. As you increase the temps the more efficient the stove burns more of the smoke gases. Thats how a wood gasifier boilers burn more efficient than a wood stove.
    ScotO likes this.
  23. precaud

    precaud Minister of Fire

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    Sure, it does a good job of blocking radiation that NEVER REACHES IT when it is dirty!
  24. Huntindog1

    Huntindog1 Minister of Fire

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    Yep, its hard to believe their claims its almost magical. Only product I found to make that claim.
  25. precaud

    precaud Minister of Fire

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    I'm with you, Scotty. I want the most heat out of the stove. What confuses things is, in discussing this, different people use the same words with different meanings/connotations behind them. For example, efficiency. Is it measured by emissions? By wood consumed vs heat produced? By stove surface temps? By how long your stove "stays hot"?

    I think the best measure of an EPA stove's ability to deliver the most heat is it's Firebox-Volume-to-Weight Ratio. Kinda like power-to-weight ratio that race car enthusiasts use. The higher the ratio, the more heat the stove will produce in a given period of time.

    The most efficient stove is going to burn cleanly and then do a good job of extracting the generated heat as and when it is produced and getting it out into the room. What is described here is not a heat storage system. Storage inevitably involves energy loss, and the losses will be greater where the temperature differentials are the greatest (i.e. firebrick). So, instead of trying to store heat in the firebox lining, get it out into the room and have your "storage" there.

    I have examples of this here. I have two clean-burning stoves, identical firebox sizes lined with IFB, one weighs 100 lbs less than the other. Guess which one delivers more heat into the room from one load to the next? There's no comparison. It's directly proportional to the weight difference.

    If you're going to store heat in a stove, do it away from the firebox.

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