Materials used to line fireboxes - a test

[precaud]

For the first time in decades, I am 602-less. Kinda weird.

 

[johnn]

best of "Luck", precaud,,,dealing with your seperation anxiety :ahhh:

 

[precaud]

sorry, double post

 

[precaud]

Thanks ml, it didn't last long... within minutes after that post, I felt total relief!

 

[BrotherBart]

For the first time in decades, I am 602-less. Kinda weird.

Post-Jotul depression?

 

[precaud]

Irrational, for sure. Guess you could say it had cast a spell on me.
My steely resolve was quickly restored by lighting up the X33.

 

[BrotherBart]

Irrational, for sure. Guess you could say it had cast a spell on me.
My steely resolve was quickly restored by lighting up the X33.

You were baffled I am sure.

 

[precaud]

You were baffled I am sure.

Totally. But admittedly, that was secondary.

 

[jeff602]

Durability is also a factor in fireboxes. It took almost 20 years for my Jotul 602's inner burn plates to warp and crack. That's pretty durable and the servicing of them was fairly easy. The outside castings of the stove still look like new.

where were you able to locate the side liners for an older Jotul 602 mine need replaced one is warped and cracked other cracked.

 

[begreen]

I got them from Stove Parts Unlimited. See link for their catalog in the other thread that Rick spun off of this question. Local dealer should also be able to get them for you if that's more convenient.

Inspect the upper baffle plate closely as well. Ours was warped and needed replacing with the side plates after 20+yrs. service. The good news was that afterwards, the stove performed better than it had in years.

 

[karri0n]

To this day, this is my favorite thread on hearth.com

 

[Battenkiller]

This is a very interesting thread, one that I wish I was part of when it was unfolding. Still, there is a lot of contradictory info given, with most of the techniques being useful to forge technology, where the idea is to keep the heat inside to keep temps up in the forging range. The cook stoves mentioned, like the Rocket stove, are open stoves that work by getting the internal gases extremely hot so combustion is complete and greater efficiency is achieved. In these designs, you are actually cooking over the searing hot flue gases themselves, not with heat conducted through the stove surface and into the pan bottom. Sure, you want high internal temps in a wood-burning heating stove as well, but you also want to get the heat transferred out of the firebox and into the room, not up the flue.

There was no explanation here of the physics behind the ability for ceramic insulation to simultaneously raise internal temperatures and still transfer heat efficiently through itself to the stove walls. Temperature doesn't get transferred, heat gets transferred. All insulating materials work by slowing down the rate of heat transfer - period.

My wife's glass kiln uses electric resistance coils embedded into low K-value insulated firebrick, which serves as the interior lining of the chamber. Internal temps gets as high as 1400ºF, yet the steel jacket on the outside only gets a few hundred degrees, even if the stove kiln has been running all day at that temp. If heat was efficiently transferred through insulating firebrick, shell temps of her kiln would get even higher that stove temps, yet clearly, this is not the case.

There are other inaccuracies as well, such as the color white being IR reflective, and this is simply not true. White is reflective only is the visible range of the spectrum. Refractory coatings like ITC-100 don't dry pure white and they do a fine job of reflecting IR radiation. People often get these things confused because a black object gets hotter in sunlight than a white object, but that has to do with the enormous amount of visible light energy that sunlight carries. Black things look black because they don't reflect visible light. Don't assume this carries over into the infrared world. According to the first law of thermodynamics, energy is always conserved. If no visible light is reflected from a black surface, it must be absorbed. The energy from the light will be converted to heat energy and raise the temp of the material. It will then be emitted as IR radiation (or conducted into your hand, making it feel warm to the touch). That radiation will then strike other objects and change from radiant energy to heat energy. The actual color of these objects is irrelevant to their ability to absorb or emit this IR radiation. I'm not an engineer, so if any engineers or physicists here can show me I am wrong about this, I will gladly retract this statement.

 

[karri0n]

This is a very interesting thread, one that I wish I was part of when it was unfolding. Still, there is a lot of contradictory info given, with most of the techniques being useful to forge technology, where the idea is to keep the heat inside to keep temps up in the forging range. The cook stoves mentioned, like the Rocket stove, are open stoves that work by getting the internal gases extremely hot so combustion is complete and greater efficiency is achieved. In these designs, you are actually cooking over the searing hot flue gases themselves, not with heat conducted through the stove surface and into the pan bottom. Sure, you want high internal temps in a wood-burning heating stove as well, but you also want to get the heat transferred out of the firebox and into the room, not up the flue.

There was no explanation here of the physics behind the ability for ceramic insulation to simultaneously raise internal temperatures and still transfer heat efficiently through itself to the stove walls. Temperature doesn't get transferred, heat gets transferred. All insulating materials work by slowing down the rate of heat transfer - period.

My wife's glass kiln uses electric resistance coils embedded into low K-value insulated firebrick, which serves as the interior lining of the chamber. Internal temps gets as high as 1400ºF, yet the steel jacket on the outside only gets a few hundred degrees, even if the stove kiln has been running all day at that temp. If heat was efficiently transferred through insulating firebrick, shell temps of her kiln would get even higher that stove temps, yet clearly, this is not the case.

There are other inaccuracies as well, such as the color white being IR reflective, and this is simply not true. White is reflective only is the visible range of the spectrum. Refractory coatings like ITC-100 don't dry pure white and they do a fine job of reflecting IR radiation. People often get these things confused because a black object gets hotter in sunlight than a white object, but that has to do with the enormous amount of visible light energy that sunlight carries. Black things look black because they don't reflect visible light. Don't assume this carries over into the infrared world. According to the first law of thermodynamics, energy is always conserved. If no visible light is reflected from a black surface, it must be absorbed. The energy from the light will be converted to heat energy and raise the temp of the material. It will then be emitted as IR radiation (or conducted into your hand, making it feel warm to the touch). That radiation will then strike other objects and change from radiant energy to heat energy. The actual color of these objects is irrelevant to their ability to absorb or emit this IR radiation. I'm not an engineer, so if any engineers or physicists here can show me I am wrong about this, I will gladly retract this statement.

The data shows here that it's not the insulating or r-value we're looking for, but low mass and high refractory ability. Another factor to consider here is that most stoves do not have insulating material on every surface of the firebox, notably the stove top(which is where I believe precaud took his readings, and is often the most paid attention to surface on the stove in terms of heating). I'd imagine your wife's kiln is also not designed to be a space heater, and probably has either some shielding or some convective means that cools the outer surfaces. If not, I think the UL would take issue with a device that is not a space heater getting hotter than a space heater.

Bear in mind that the front glass is far from an insulator, and the entire flue gas path is generally designed for good heat transfer, with bare metal being above the baffle in the exhaust stream. I would also venture that, for a majority of stove installs, people aren't putting them in the center of a room where heat radiating outward from all sides is ideal. many people install a stove in a hearth or alcove, where radiant heat from the back and sides will be going directly into a wall, or worse, a masonry mass that has an exposed to outdoor surface. A higher internal temp, and more shielding on the back and sides, equals more heat into the actual living space.

Higher internal temps will always result in a cleaner burn,Though I can agree with you that if no other variables are changed, you very well may end up sending more btus up the flue this way.

 

[PAJerry]

Very interesting thread! I managed to get a box of PA-23 insulating firebrick from one of our suppliers (an advantage of working in a foundry). I had need for only 1 brick since one in the back of my Vista broke but he gave me the whole carton. Anyway, the new brick weighs about 1/2 as much as the originals. I will be replacing the rest after the season is over so next winter will be interesting, seeing if the heat output, which is already very good, gets even better. I burn mostly slab wood since it is easier to use in a small stove, but when I have burned cord wood, I seem to get a lot of 'clinkers' rather than the fine ash. Maybe the IFB will help in that regard. If anyone wants to check, there is a lot of technical information at the BNZ Materials website. I had toyed with the idea of using 1" kaowool as a stove lining as it is amazing material - at work it can be red hot on one side and you can place your bare hand on the other - but it is probably too fragile to hold up long. Maybe the IFB will do as well but hold up better.

 

[Battenkiller]

The data shows here that it's not the insulating or r-value we're looking for, but low mass and high refractory ability.

Not sure what we're looking for, but Precaud is using insulating ceramic material for its insulating qualities:

-The measure of this is called Thermal Coefficient, K for short. A high K says the material readily collects and stores heat. A low K says the material is a good insulator, and resists the flow of heat through it.

-As you can see, cast iron and the heavy firebricks are poor insulators. It’s no coincidence that they were widely used in pre-EPA stoves, when designers were trying to pull as much heat as they could OUT of the firebox. The lightweight firebrick is the better insulator by far

-High insulation and low mass is best.

-Ceramic refractory is a superior lining material, giving better insulation AND better heat transfer through the walls.

The claim is that cast iron liners are inferior because of their poor insulating qualities, and that dense firebrick will only slow down the "response time of the system". This is not explained, but I'm left to assume that these materials don't insulate but merely slow down the heat loss from the stove. Well, that's all any insulator does. A basic tenet of heat transfer is that heat will always flow from a material with a higher temperature to one of a lower temperature until equilibrium is reached. Insulators can only slow down the rate of heat loss, not stop it.

I'd imagine your wife's kiln is also not designed to be a space heater, and probably has either some shielding or some convective means that cools the outer surfaces. If not, I think the UL would take issue with a device that is not a space heater getting hotter than a space heater.

The kiln is certainly UL approved if installed as per instructions. I welded up a custom steel stand for it, and the kiln itself sits up on three insulated firebricks placed on their sides. The insulating firebrick interior retains the enough heat inside the kiln that skin temps are relatively low. Temperature is controlled with an infinite switch via a thermocouple and a programmable digital controller. Without the switch and controller providing temperature control, both internal and external temps would continue to rise until the unit was producing as much heat externally as a space heater of the same wattage/BTU rating. That's the beauty of using thermodynamics to analyze a system, the basic laws can never be ignored.

Higher internal temps will always result in a cleaner burn,Though I can agree with you that if no other variables are changed, you very well may end up sending more btus up the flue this way.

Clearly, the EPA stoves work to give a cleaner and more efficient burn. Hotter temps and correctly administered secondary air seem key to the non-cat stoves. Many of the older designs achieved extremely hot temps in the primary burn zone the old fashioned way - by delivering air at higher velocities directly through the coal bed. This also creates turbulence, which increases the mix of air and wood gases before they have a chance to escape the intense heat of the primary burn zone. The only place I can see that insulation helps is in retaining heat in the secondary burn zone.

A lot of thought and engineering has to go into this just to keep a few grams of particulate matter out of the exhaust gases. The last chapter has not been written in this story, so I suspect that the stoves of 2020 will have more going on than the stoves of today. I applaud all of the thinking that goes into these possible improvements. All I am saying is that there are omissions in the explanation of how this material might improve a stove. That is does improve a certain owner's stove in a certain set of circumstances... well, I'm not disputing the data that Precaud provided. His thermometers did their job, and he dutifully reported the results here. What the mind sees, the heart must believe. I'm just not convinced it is happening for the reasons claimed.

 

[maxed_out]

Well, I spent some time reading thru the firebrick discussions over the weekend and all I can say is wow!. Its good to know I'm not the only one pondering this stuff. Good to know one is not alone.

Anyway, its time to order firebricks for the (used-2007) Quadrafire Isle Royale. My first season with it! Theres a couple cracked and the back ones with the holes are pretty bad. So after reading thru the thread, I have to ask which ones should I use? Pummice, clay or other. Clay on bottom? pummice on sides? Fire away.

The guy I got the stove from seemed to think there is some type of upper firebrick required. I havent seen a real live stove or studied the pics enough to know. If anyone can help me with this let me know as well.

thanks!

 

[precaud]

I'd stick with the pumice brick. No clay. You can safely move the broken/cracked ones to the bottom, ash will fill them in, no problems. You probably will have to buy the ones with holes drilled.

I don't think there is "upper firebrick" on these, it's most likely a high-temp ceramic fibre board. You can download the users manual for your stove on Quad's website, all the details should be in it. Enjoy your stove.

 

[maxed_out]

precaud, thanks for your advice and all the testing and sharing you've done on this topic. Been an eye opener. I'm headed for the pumiced land.

 

[maxed_out]

Just a brief update on this QF IR. I'm finding the pumice firebricks really easy to work with and cut. I setup my radial arm saw with a masonry blade-cuts very well. Some dust so if your travel this road do it outside. I used a small masonry bit in my drill, made a swiss cheese hole pattern and knocked out 2 pretty good if I dont say so myself holes.

The upper baffle refractory-above the air tubes? Dealer wants 50. Is that what I want to do? I thought I saw somewhere in this thread another source but that remains elusive. If anyone knows a source or another means to save any $ over the dealer quote please post.

I think after I get the baffle in, she'll need some of that stove magic wipe on stuff and then bring on the cold.

Oh yeah forgot to ask...35 for fiber handle also seems harsh. Anyone got a better way here as well?

 

[vvvv]

if the wood gassifies too fast for the available supply of combustion air its an inefficient burn

 

[precaud]

Well done, maxed. Did you buy the pumice bricks from Quad? How much were they?

Pricing on the fiberboard baffle is a hard call. So far, noone has been able to find a place to buy small quantities of this stuff, except through a dealer. It's higher density than the stuff available through normal retail channels. 50 doesn't impress me as a terrible price.

 

[maxed_out]

The bricks were 5 a piece from the dealer. The 2 piece set with the holes were 30 for the set so I saved a little there. I think I have enough bricks that if needed I could go 2 deep on the bottom. Who knows what thats gonna do.

On the baffle, do you think kaowool would work? Maybe thats more of a insulator than a refractory material. I guess I could use a clay sheet of firebrick if I could get something close to the right thickness.????

Or you can stop me from trying to jump thru flaming donut holes and just buy the sheet from the dealer.

 

[precaud]

Why would you want to go 2 deep on the bottom? Only makes your firebox smaller.

Kaowool is too soft, it has poor abrasion resistance. I get away with it in the X33 because the firebox is so tall and wood never even gets close to it. In your Quad it would get chewed up in no time. The standard baffle material is a high-density version of Kaowool. No clay! Just buy the sheet and be done with it, and don't jam wood into it when loading. If you have any 1/4" kaowool blanket laying around (every household should...) put a layer of it on top of the board. It seals any leaks around the edges of the board and provides more insulation. Quad started doing it on most models a few years back.

 

[maxed_out]

precaud, On the bricks just me being thrifty! I'll put them away for a rainy day.

Kaowool on top of the board. I'll do that.