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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. skidud

    skidud Member

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    Can someone tell me the differences between the light weight and the regular fire brick? My manual calls out the use of both and I noticed that the last owner had them installed in a different order than the manual states. I guess I'm interested in knowing which one insulates better and what kind of difference there would be if one were swapped for the other. Thanks

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  2. FyreBug

    FyreBug Minister of Fire

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    The insulation qualities of either are almost identical. The heavier refractory bricks however will last year's if not decades. Whereas softer pumice bricks might only last you a couple seasons or more depending on usage.
    ScotO likes this.
  3. skidud

    skidud Member

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    I read somewhere that the pumice bricks were better and worth the shorter lifespan. I guess I couldn't figure out the actual difference besides they were softer and had shorter lifespans. I also wasn't sure if the pumice bricks were indeed what my manual refers to as light weight. I'll have to do some research on pumice bricks then. I've got enough of either to completely reline the stove but want to use the best brick.
  4. BobUrban

    BobUrban Minister of Fire

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    Not sure if one is better insulating than the other but we use both in our forge and it gets in the 2000 degree range. I do know when I am heating finished blades for normalizing and heat treat I use a small chunk of either to keep the blade off the forge floor for more even heat. If I leave a small piece in the center of the forge it will melt - no matter which type I am using :)
  5. Todd 2

    Todd 2 Feeling the Heat

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    The light ones came in my summit new, the third season they started to powderize and break ( bumping them with bigger splits when loading full ) Installed the heavy solid clay ones and they seem to be much more durable ( the dealer said they would last alot longer. The only difference I can tell is that with the new heavy ones the stove seems to take a little longer to heat up on cold starts, but on the plus side the stove seems to be warmer at the end of the burn cycle. 20 - 25 deg. warmer surface temp. They don't move around when you catch the edges of them with your ash shovel or chip as bad as the light ones either. As far as installing them I followed the mfg. instructions, one would think that is how they tested them and maby gives the best fire box protection & performance. As far as insulating, I can't really tell any difference.

    What part of northern OH Skidud ?
  6. precaud

    precaud Minister of Fire

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    Now that is a flat out lie, and from someone who knows better. Spare us further displeasure and correct your own mistake.
  7. begreen

    begreen Mooderator Staff Member

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    Our pumice bricks are going on 4 seasons and still look good. I don't have the numbers but I thought they have a significantly higher insulative value due to the trapped air in the pumice.
  8. oldspark

    oldspark Guest

    ." Hardbricks are very dense
    and durable and used for their structural
    qualities. They can be found most often as
    the main building component of large kilns,
    chimneys, fireboxes and burner ports—anywhere
    around direct flame. Softbricks are
    lightweight and made from a refractory
    clay body containing combustible materials.
    When fired, the materials burn out
    leaving a sponge like matrix of air pockets,
    which serve to provide insulating qualities
    to the brick. Also known as insulating firebricks
    (IFBs), these bricks absorb about half
    the energy as hardbricks during a firing.
    Softbrick range from 2000°F to 3300°F
    and are used as the brick of choice for constructing
    electric kilns or as insulating liners
    in reduction kilns."
    Jags likes this.
  9. Jags

    Jags Moderate Moderator Staff Member

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    Ummm...still on the original pumice bricks (8 yrs). "A couple of seasons" may not be accurate. And YES, there IS a difference in the absorption and reflective properties of the two types of bricks.
  10. precaud

    precaud Minister of Fire

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    Yes, by a factor of 4 to 6 over the clay firebricks. And as I've pointed out many times, the high thermal mass of clay bricks works further against their effectiveness in a place where low-mass, high-isulation factors are needed. Clay bricks are used solely for economic reasons, not for performance.
    Jags likes this.
  11. FyreBug

    FyreBug Minister of Fire

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    Some facts regarding bricks:
    • K factor for either pumice or refractory almost identical
    • Heat transfer for either almost identical
    • Heat retention is much better for refractory due to its mass
    • Mechanical properties much better for refractory
    • Weight of pumice about 1/3 of similar size refractory
    • Cost of pumice about 1/3 less than refractory
    I can post the MSDS if you'd like.

    Why would a MFG use pumice vs. refractory? 1) On a larger wood stove you save almost 50Lbs in shipping weight. You can therefore cube out before you weight out. ie. saves on shipping. This is particularly important for imports 2) Cost: Obviously there is cost savings associated with the brick itself.

    Since we use both, we are well aware of the properties of either. We use the lightweight bricks for our 'value' brands and the heavier for our premier brands.
    ScotO and raybonz like this.
  12. madison

    madison Minister of Fire

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    Thanks for the info FyreBug and all responders.

    4th or so season with the OEM soft brick with my T6, after the first yr, the bricks in front of the stove (@ the air inlet) started to deteriorate and now have lost ~ half of their thickness, I have flipped and rotated these with the rear and side bricks. I picked up some hard bricks at Tractor Supply for replacing, but have not used them yet. I will try these heavier bricks in the front in the future...

    Soft bricks are not locally available .
  13. precaud

    precaud Minister of Fire

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    When I looked into is a couple years ago, normal "refractory" firebrick K factors were between 4 and 15, with ones used in stoves averaging about 5.5
    Pumice and other IFB were in the 0.88 to 1.1 range. That's hardly identical.

    If they're the same size yet 3 times the weight, then heat transfer cannot be identical.
    And why does one want "heat retention" in a firebox lining? In reality, the insulating properties of the liner become undesirable as soon as the flames die, just like secondary air. The more heat "retained" in the firebox, the more is carried away up and out the chimney, due to the "always-on" air systems.

    Directly related to the weight. The higher-density IFB's are just as good, though prohibitively expensive.

    And is that a bad thing?
    Huntindog1 likes this.
  14. TMonter

    TMonter Minister of Fire

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    Not true. Pumice bricks are an insulating firebrick and the dense bricks are not. If you look at a refractory schedule for both you will find a immensely higher insulating value on the pumice versus refractory brick. (Experience from working with both products in boilers).

    Dense firebrick is used for wear value, not necessarily insulating value.

    I don't have the refractory schedule I used to have handy but I did find this:

    http://stoves.bioenergylists.org/stovesdoc/Andreatta/Heatloss.htm

    Remember maintaining a good clean burn with the secondaries on a modern stove requires that the temperatures remain relatively high. Pumice bricks are good for doing this while dense firebricks are not.
    Huntindog1 and raybonz like this.
  15. begreen

    begreen Mooderator Staff Member

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    Please do. And tell me where I can find pumice bricks for anywhere near 1/2 cost. Everywhere I have checked has them at about 2x the cost of common firebrick. Though you mentioned refractory which I don't believe is the same animal. Maybe we should be sure we are talking about the same products here? The MSDS will help.
  16. BrotherBart

    BrotherBart Hearth.com LLC Mid-Atlantic Division Staff Member

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    What I have said here for years was probably the reason for using the things.
  17. TMonter

    TMonter Minister of Fire

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    But 50 lbs on something that heavy which is going freight anyway unless it's air freight, isn't going to significantly change the price unless you're at a common break point for weights.
  18. FyreBug

    FyreBug Minister of Fire

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    I should have said around 1/3 less on the cost. At retail the cost differential might be around 10% 15% less. (we do anyway - dont know about other vendors)

    I've asked for the MSDS but something to ponder on in the meantime... If pumice provided a distinct advantage in efficiencies and caloric values, you would think all MFG's would avail themselves of this advantage. However, many 'premium' brands despite the shipping weight disadvantage and revenue loss on replacement parts and higher cost of the heavy duty brick brings to the unit see this as a benefit. This is a Lopi video where they discuss the advantages of the heavy bricks around the 1 min. mark.


    Finally, I'm a bit puzzled by the argument against additional mass in the firebox. This is seen as a benefit for thermal mass heaters such as Tulikivi and brands such as Heartstone which line their firebox with soapstone. Not to mention cast iron stove. More mass evens out the heat curve for radiating heat for a longer time. This is typically seen as a benefit not as a detriment.
    raybonz and ScotO like this.
  19. oldspark

    oldspark Guest

    Well I wondered about this a couple of years ago and did not find out what I wanted to know, maybe now we will get some good answers.
  20. Jags

    Jags Moderate Moderator Staff Member

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    Something else to ponder (and I mean that, I don't have the answer), is it possible that the pumice style, with better insulating properties is used in places to protect the shell of the stove? As an example - my Isle Royale only requires ember protection - no specific R value for the hearth pad. It also uses the pumice style bricks on the bottom. Simply coincidence or intentional? Inquiring minds want to know.
    rideau likes this.
  21. begreen

    begreen Mooderator Staff Member

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    The video is a sideline, not on topic. Lopi has a reputation of building tough stoves. Conventional firebrick is tougher. Lopi smartly is touting this as a feature, the same way SBI boasts the toughness of it's c-cast baffles. Good marketing but a bit off topic I think.

    It will be interesting to see what firebox insulation materials are used in the new stove challenge. My guess is that they will be using some more exotic thermal insulation and maybe pumice bricks. But I wonder how many will be using regular firebrick? My guess is none, but I could be wrong.
    Huntindog1 likes this.
  22. Huntindog1

    Huntindog1 Minister of Fire

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    I have recently been looking into the different brick types as some of you know I recently put a 1/4" ceramic insulation behind all of my firebrick, sides and bottom.

    I was also looking into using a more insulative firebrick.

    What I found is that firebrick can have a higher alumina content and are rated as such as what percentage they have of alumina in some fire brick.

    As there is another aspect of firebrick that was mention and that is its reflective properties. Heat radiation can be reflected back into the fire box.

    I suspect that the alumina content may point to how well it reflects heat. But it may conduct heat more , I am not sure.

    Ceramic and ceramic made from alumina is said to be more highly reflective material. It also can also take more heat.

    Take a look at this webpage and notice what it says at the bottom about efficiency.
    http://hotkilns.com/reflective-coating

    Think of your old fashioned thermos bottle had the highly reflective almost mirror like glass liner with a vacuum air space all around as in insulator.

    So would it be better to use the more reflective fire brick with ceramic insulation behind it.

    Insulative fire brick points to less conduction of heat , then fire brick that are more reflective points to reflecting the heat radiation back into the fire box.

    As with heat you have convection,conduction and radiating heat (heat radiation).
  23. TMonter

    TMonter Minister of Fire

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    But that isn't what has been claimed. It doesn't have anything to do with efficiency directly but rather keeping temperatures up in the firebox during extended burns so that the secondary burn system stays lit. If the stove is designed with insulating firebrick swapping it out can have detrimental effects on how fast the stove heats up and how it performs.
  24. milner351

    milner351 Member

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    Interesting. My Summit factory bricks are starting to erode, one has broken. The vertical bricks on the sides seem to be taking more of a beating than those on the floor of the firebox. I've been wondering what the best course for replacement would be.

    Thanks for the information, I have some pondering to do.
  25. FyreBug

    FyreBug Minister of Fire

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    I have reviewed the MSDS, however it doesn't list any of the caloric qualities of the bricks; only the Health & Safety Hazards. I'll make a request of engineering for their comments since I would also like to get a definitive answer. However, at this time of the year they are up to their neck in projects and workload so I wont push too hard.

    I will offer this comment though... Performance, BTU output, emissions etc... is the 'holy grail' of all wood burning appliances MFG and their engineers. They talk to all types of suppliers and review components performance on a regular basis in order to get an edge. Many have their own labs so they can test to their hearts content.

    If a particular brick provided a significant performance advantage, they would immediately ensure to use this particular component. Instead what do we see in the market? Heavy duty bricks are favoured by many (not all) higher priced units despite weight, cost and replacement part income loss. Some of what are considered very high end will use Skamol (Scan), soapstone (Hearthstone) or a high grade of vermiculite (Valcourt).

    Therefore, based on this I doubt very much the performance is enough to justify all this debate in smaller fireboxes. It could be that in larger applications such as Kiln and large commercial/industrial ovens it provides better benefits. I would also suggest the advantage of using one firebrick over the other has more to do with financial considerations than anything else.

    Keep in mind the efficiency testing is relatively easy with the 'stack loss' method. Therefore comparing either or any bricks is not a big deal and no doubt most engineers are aware of the differences if any...

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