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Using ceramics in stove?

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by leoibb, Oct 14, 2012.

  1. leoibb

    leoibb Member

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    hello all. a question i have had in my mind. i was wandering. the old gas fires used ceramics to send the heat out, i wandered why they are not used in stoves? incorporated in to the baffle maybe and flames would hit them and then they get to glow thus throwing much more heat out? am i on the wrong track thinkingf ths? anyone tries it?
    i figure most the heat from the stove is from the logs glowing red and the ceramics would do the same thing? im quite tempted to somehow try this as an experiment to see if it does work

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  2. rideau

    rideau Minister of Fire

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    Would ceramic be more subject to damage from direct flame? I now the glass windows are ceramic, but flame doesn't hit them directly....I know flame impingement on ceramic cats is a major concern.....could call Woodstock and ask them for their opinion on this idea....they'd figure out the answer for you, I'm sure...
  3. Backwoods Savage

    Backwoods Savage Minister of Fire

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    Don't some stoves already use some ceramics?
  4. begreen

    begreen Mooderator Staff Member

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    They certainly do, in catalytic combustors.
  5. Backwoods Savage

    Backwoods Savage Minister of Fire

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    My point exactly.
  6. leoibb

    leoibb Member

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    thankyou for the replies. i did some reading on these cats and they are coated in some metal? however the cost of these is very high compared to ceramics of a gas fire. i suppose it is more a question of would using them generate more heat?
  7. leoibb

    leoibb Member

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    i will do some research on this. but thankyou for your imput.
  8. begreen

    begreen Mooderator Staff Member

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    Yes, like the catalytic combustor in a car, there is a rare metal catalyst coating on the ceramic, usually palladium for wood stoves. Some everburn stoves also use ceramics without a catalyst.

    The ceramic honeycomb in a gas stove works on a similar principal, but with some significant differences. In a gas stove there is a continuous supply of simple molecules of clean gas. The ceramic honeycomb is designed so that the gas flows through many parallel holes to the largest possible surface area for complete combustion. It's easy to control the flow of this gas across the honeycomb with a manifold.

    Wood gas on the other hand is not clean, nor consistent. It's a complex, somewhat diry gas with a lot of compounds, varying to a degree with the wood source. The gas peaks in the early part of the burn, then tapers off as the wood turns to charcoal.

    The difficulty in making a gas stove's ceramic to work in this case would be to pipe the wood gas to the ceramic at the appropriate time. Not too early or it might clog. The ceramic needs to be hot to work. That means the stove needs a bypass system for starting the fire. Everburn stoves like the Lopi Leyden and Harman Firedome stoves use a variation on this technology, routing the hot wood gas through a ceramic maze, but without the honeycomb.
  9. leoibb

    leoibb Member

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    thankyou for that , my consideration was to run it across the front of the baffle plate where the secondary burn happens as all the flames take that route to exit ...mmmm needs some thought i think
  10. begreen

    begreen Mooderator Staff Member

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    Here's a rear-side cutaway of the Leyden.

    leyden back.PNG
  11. Huntindog1

    Huntindog1 Minister of Fire

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    If you notice alot of cat stoves are designed so the the cat is mounted on edge so the flame cant directly go straight up and into the cat. Thermal shock is an issue as it can crack the ceramic cat.

    See how the cat is in this stove and the path the smoke must take to get to the cat so no direct flame can get to the cat.

    progress.PNG
  12. BrotherBart

    BrotherBart Hearth.com LLC Mid-Atlantic Division Staff Member

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    What would be different Non-cats have ceramic firebrick in them and forms of ceramic fiber boards or blankets for baffles. The stuff in the old gas stoves was the same stuff the firebricks are made of.
  13. Huntindog1

    Huntindog1 Minister of Fire

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    The ceramic cats are most likely sensitive due to them being thin ceramic. The honey comb structure and the fact they are made to heat up to activate.

    Dont know what ceramic does for the transfer of heat.

    Ceramic burn chambers for gasifier wood furnaces are for the fact the burning of the wood gases creates temps of 2000 degress in the ceramic burn chamber and it takes the ceramic chamber to withstand those temps as metal would not survive those temps.

    As for a wood stove the concepts is too keep the firebox hot to let the secondary burn tubes re-burn the smoke before its escapes up the flue.

    The concept is that these stoves have very little air flow as once you get the firebox temps up it takes very little air to burn the smoke a such high temps.

    Its the slow movement of air thru the stove that gives the heat time to radiate out the top of the stove and out the front glass of the stove.

    If you open the door the air movement and quantity increases and the heat has very little residual time in the stove in which to radiate out the top and front.

    Using firebrick with higher insulative properties, such as pumice bricks, works to keep the fire box hotter thus burning more efficiently which means more heat. And if you can keep the temps up hotter inside the firebox you can set the stove to lower input air settings and still keep the smoke burning mode going as in secondaries firing in the top of the stove.

    So what that gives you is a lower air setting means slower air movement thru the stove and more residual time for the heat before it goes up the chimney. The more residual time the more heat radiates out the top and front of the stove, which those locations are not insulated and you get alot of heat radiated out from the top and front.

    You notice on alot of these stoves the blower in the back has air coming up the back of the stove and hitting a bent back heat shield that dieflects the air flow over the top of the stove to take that heat radiating off the top of the stove and sends it out into the room. At first glance one would think the heat is mostly coming off the back of the stove but its actually getting most of the heat to blow off the top of the stove.

    So as far as fire bricks are concerned there are ones that basically fire resistant and durable then there are ones that insulate but are not as durable. There are fire bricks that store heat better(soapstone). Then there are fire bricks that reflect heat back to the center of the fire.

    Ceramic fire bricks or chambers? All I can say is ceramic can with stand very high temps.

    Ceramic insulation and boards are usually rated at 2300 degrees.

    I just bought 1/4" ceramic insulation and put a layer behind my firebricks to increase the efficiency of my stove.
    rideau likes this.
  14. rideau

    rideau Minister of Fire

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    Huntingdog, Thanks for a well-explained informative post.
  15. begreen

    begreen Mooderator Staff Member

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  16. Huntindog1

    Huntindog1 Minister of Fire

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    Here is some info on Wood Stove Ceramic and Stainless Steel Cats.

    http://www.chimneysweepnews.com/Combustors.htm

    But I guess as far as the OP original question of what can ceramics do for Wood Stove performance, we havent really answered your question.

    Its basically really just used as a high temp substrate for insulation and fiber boards.
  17. Huntindog1

    Huntindog1 Minister of Fire

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  18. Huntindog1

    Huntindog1 Minister of Fire

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  19. Huntindog1

    Huntindog1 Minister of Fire

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    Well it looks like alumina content of a fire brick is the same as saying it has ceramic content to the brick. There are different percentages of how much alumina is in fire bricks.

    If you look up alumina it is used to make ceramics. So not sure whats the difference between alumina and ceramic.

    There are fire bricks out there claiming to be ceramic fire brick, I think due to high levels of alumina in the brick. But I am not sure on this.

    These bricks are interesting:

    http://hotkilns.com/reflective-coating
  20. begreen

    begreen Mooderator Staff Member

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    ?? I think the question about performance was answered directly. Did you read the whole thread??
  21. Wood Duck

    Wood Duck Minister of Fire

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    The original question is whether placing ceramics in the firbox so that the ceramics get hot and thus increase heat output from the stove. I think the answer is no. Ceramics might be able to extend the heat coming from the stove the way soapstone does, but the extended heating is at the expense of quick heat output when the stove is first lit. The soapstone doesn't create any heat and neither would the ceramics, both simply absorb and then reradiate the heat from the fire.

    I am not trying to argue that ceramic firebricks are a bad idea is a stove just commenting on the notion that additional ceramic added to the inside of the stove in a manner that does not create additional insulation for the firebox won't increase heat output. I don't know whether additional insulation is better or not, or whether coating the firebricks with space shuttle tiles would increase efficiency, but I think there is some point where additional insulation would be counter-productive. All wood stoves are designed to contain the heat of combustion to some degree and thus make the fire burn better or more efficiently, but we also want heat to escape into the room, and excessive insulation might hamper heat transfer too much. Why do stoves have the amount of insulation that comes from the manufacturer. I'd like to think because it is the optimal amount, but maybe not.
  22. leoibb

    leoibb Member

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    slightly different but does anyone wrap there baffle plate with a material?
  23. Huntindog1

    Huntindog1 Minister of Fire

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    Most of those baffle plates are Ceramic material. Alot of stoves have a blanket of ceramic insulation laying on top of the baffle board to add to the abiltiy of the stove to keep the heat up around the secondary burn tubes.
  24. Huntindog1

    Huntindog1 Minister of Fire

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    Wood Duck,

    Just in general the idea of increasing the heat of the firebox is to do it at the lowest setting of the stove. As when your turning the stove down your turning it down to a point to keep your secondary mode going.
    As its a combination of how much heat is in the box and how much air is going in. So once you reduce the air and it reduces the amount of fire then the secondaries will go out when the heat level drops. . Wes999 already tried these tricks in his stove to improve the performance at the lowest air settings of the stove. His results were he was now able to keep his secondaires firing at his lowest input air settings due to it being easier to maintain that heat threshold for secondary mode of operation. Just for added information last week I insulated my fire box with about $30 worth of 1/4" ceramic insulation behind the firebrick and the performance boost at low settings is very noticeable, you can look my post up in the DYI forums.
  25. leoibb

    leoibb Member

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    hi thanks for that. ive been searching for the ceramic products to use but there is so many. which or what did you use? also what could i wrap the baffle plate with that will withstand the flames? any options and were to buy would be great?

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