Soapstone replacement for insert firebrick

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SolaGracia

New Member
Dec 24, 2009
32
Northeast Ohio
Does anyone know if is would be possible/advantageous to replace the factory firebrick in an insert with soapstone shaped as duplicates?

I would like to get longer periods of heat output once the fire dies down for overnight burns.

My insert is the Regency i3100l.
 
Welcome to the forum SolaGracia.

I'd stay with firebrick. The key to longer burns is in the wood that you burn.
 
SolaGracia said:
Does anyone know if is would be possible/advantageous to replace the factory firebrick in an insert with soapstone shaped as duplicates?

I would like to get longer periods of heat output once the fire dies down for overnight burns.

My insert is the Regency i3100l.

Of course you can replace firebox firebricks with soapstone duplicates. But, why would you want to?

Here is why I would not do it:

1. Soapstone is considerably more expensive.
2. Soapstone is soft compared to firebrick and will get scarred up more easily.
3. Soapstone has a rather high thermal conductivity compared to (fire)brick (soapstone being some 6 to 7 times more conductive;see below). This factor alone means you will LOSE heat faster from your firebox with soapstone than firebrick. From a materials standpoint, to retain heat in the stove, the firebox should be INSULATED, not conductive. This is one of the reasons the Mfg put firebrick in the metal stove in the first place.

MATERIAL                   THERMAL CONDUCTIVITY
W/mK   (Btu-in/hr-ft-F)

Cast Iron                                75 (520)
Soapstone                          6 - 7 (42 - 48)
Granite                                   3 (20.8)
Face brick                             1.29 (9)
Firebrick, Clay (ASTMC62) 0.95 (6.6)

Aye,
Marty
Grandma used to say, "Most likely, you will not have to reinvent the wheel."
 
The reason for firebrick is to be an insulator. The insulation helps maintain higher internal temperature for more complete combustion. The reason for soapstone is to be a thermal mass. This is to even out the highs and lows of the cyclical nature of wood burning. I think the two are non-interchangeable.
 
Hearthstone uses soapstone to line the inside of their fireplace insert. It will keep the firebox warmer longer than a firebrick lined insert. It has also proven to be much more durable. It is softer, so it will scratch, but it's not a beauty contest inside of the stove. It doesnt seem as brittle as firebrick and I have yet to have to replace one out of dozens of inserts sold. I have a number of customers tell me that the heat retention is so good that the convection blower doesnt shut down between the time they let the stove burn out for cleaning the ashes and they rekindle the fire. Also, coupled with the cast iron of the insert, it makes for a very even heat. I'm sure a Hearthstone dealer could sell you the bricks. A full set of Clydesdale bricks retails for $200. Not sure if it's worth the cost to try it. Money aside, it would be a fun thing to try.
 
Franks said:
Hearthstone uses soapstone to line the inside of their fireplace insert. It will keep the firebox warmer longer than a firebrick lined insert. (SNIP)

Gee. This sounds like a sales pitch and is counterintuitive, considering the physical properties of the two materials.

Any data to support your claim: "It will keep the firebox warmer longer than a firebrick lined insert."? The Hearthstone website compares soapstone to cast iron and steel for heat retention ("HeatLife"), not fire brick.

Aye,
Marty
 
Right, because I want to sell a box of stone to someone 600 miles away from me. No Pook, no data, just 25 years of burning wood and customer feedback. You can go test it at a lab, I'll use experience and common sense. YOU can try this. Heat a 4x9x1.5 inch firebrick and a piece of soapstone with a 2 torches for 15 minutes. Come back 30 minutes later and see which one is warmer.
 
No need to throw stones and no point in getting into a pissing match. I think if you spoke to the engineers at Hearthstone they'd tell you the soapstone stove was designed from the ground up with the characteristics of soapstone in mind. If a stove is engineered for firebrick, chances are they are relying on the insulating and reflective properties of the firebrick. That is why most non-cat EPA stoves will have firebrick on all 5 sides.
 
Franks said:
Right, because I want to sell a box of stone to someone 600 miles away from me. No Pook, no data, just 25 years of burning wood and customer feedback. You can go test it at a lab, I'll use experience and common sense. YOU can try this. Heat a 4x9x1.5 inch firebrick and a piece of soapstone with a 2 torches for 15 minutes. Come back 30 minutes later and see which one is warmer.


The soapstone will be warmer, because the firebrick will have done exactly what it's supposed to: reflect the heat.

Lining a steel or CI firebox with soapstone when it is engineered to be lined with firebrick will lower the temperature inside the firebox during the burn, and very well may prevent any secondary burn whatsoever.

Franks,

I know you've only been on this site for a couple months, so you probably haven't seen Precaud's experiments using different types of refractory inside of fireboxes. The results by and large showed that the lighter the material, along with the higher of the refractory propertes of the material, are what contribute to better temps inside the firebox and greater efficiency of the stove. this is the same reason Quadrafire uses pumice brick as opposed to standard firebrick. Adding thermal mass to the inside of the firebox makes it take that much longer to reach optimum secondary combustion temp. If I recall correctly, the best material that he tested a far as refractory properties and real-world stove temps was Skamol refractory liners, with lightweight pumice bricks coming in at a close second place. Here is the thread:

https://www.hearth.com/econtent/index.php/forums/viewthread/34651/
 
Karrion, thanks for the link there. My only point was that the soapstone would stay hot longer. Nothing to do with reflecting heat. The OP asked what the pros and cons are. I never claimed the stove would heat better, just stay hot longer. LLI, I just get defensive when I offer my opinion and someone accuses me of making a sales pitch. Wasn't looking for a pissing match.

If you reread my post and find something that I actually wrote that was not factual, let me know what it is and why.
 
Thanks for all the great information. I understand now the purpose of the firebrick is to insulate. It makes sense that the Thermal Conductivity would need to be as small as possible for this. It looks like maybe they tried to balance the coverage of the firebrick in the box? There are a decent number of square inches not covered by any firebrick at all in my insert. Presumably this is to provide some path for the heat to the outside?
 
yanksforever said:
So much for all the jealous soapstone haters! ;-)

FYI:

Most of us are not engineers and have no clue of what goes into the R & D of designing and making a wood stove, or any other accessory heating device, burn the best it can.

The stance "I've done it and it works for me and some I know" or "put a torch on it and see which is hotter after a while" is simply retrogressive thinking and may explain why todays metal wood stoves and their fuel source are a dichotomy.

Aye,
Marty
 
Most of us also lack reading and comprehension skills. When a poster says "soapstone will keep a firebox warmer longer", some folks need to read more into it and offer a rebuttal as if the poster said "Soapstone will make any stove burn better and hotter and longer can someone please try to belittle my opinion and use an expanded vocabulary to do so"

You see, when people believe what they read with little or no hands on knowledge of an subject they need to be offered simple experiments to help them understand. I claimed soapstone will stay hotter longer than firebrick which would keep the firebox warmer for a longer period of time, which it will. If you couldnt comprehend that, the torch idea is the simplest way I can help you learn. You need to get your hands a little dirty sometimes.
 
Soapstone is not typically used as an insulator like firebrick. I would not do it. What would you gain? You need to add a lot of soapstone to gain any significant thermal mass.
 
Franks said:
Most of us also lack reading and comprehension skills. When a poster says "soapstone will keep a firebox warmer longer", some folks need to read more into it and offer a rebuttal as if the poster said "Soapstone will make any stove burn better and hotter and longer can someone please try to belittle my opinion and use an expanded vocabulary to do so"

You see, when people believe what they read with little or no hands on knowledge of an subject they need to be offered simple experiments to help them understand. I claimed soapstone will stay hotter longer than firebrick which would keep the firebox warmer for a longer period of time, which it will. If you couldnt comprehend that, the torch idea is the simplest way I can help you learn. You need to get your hands a little dirty sometimes.

No offense intended. Just asked for some (objective) data to support your (subjective) statement.

I am having difficulty relating a torch, 2 different masonry products and a thermometer to an engineered metal stove with different masonry firebox liners. This "simple experiment" is missing something: metal.

Is it not logical that soapstone, with more than 6X the thermal conductivity of firebrick, will lose heat faster when placed against a metal, cast iron, which conducts heat some 10X faster than the soapstone than the same comparison using firebrick, which conducts heat some 6X slower than soapstone?

Experience is a good teacher but it is not the entire story.

Aye,
Marty
PS: You'd be surprised where my hands have been.
 
May not gain much doing that, but it would still be fun to try. I like to get my hands dirty and experiment. If those stones werent so expensive I would do it with a model in our showroom. I did once put about 50lbs of soapstone on top of a quad 3100. Those stones would still give off heat when the sides of the stove were cool to the touch. Just some fun stuff and an interesting question. Here is another question. If you "replaced" the bricks with soapstone in a steel stove, would to risk damaging the interior of the stove because the soapstone didnt reflect the heat back into the firebox? If thats the case, you would need to add a layer of soapstone over the firebrick, cutting your firebox capacity down some.

Just some ideas, not looking to get slammed or accused again
 
Marty S said:
Marty
PS: You'd be surprised where my hands have been.

Now I just think your flirting with me.
So I think I have a half dozen of those soapstone bricks someplace. I can place them along one side of a steel stove in my showroom (inside of course) replacing the firebrick. I'll burn a 4 log fire which should be on the decline after a few hours. Then, I'll take a heat reading on both sides (outside) of the stove after the fire has been just about out for an hour or so. If my theory is correct, the side with the soapstone should be radiating heat into the room longer than the firebrick side. Am I missing something with this idea?
 
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Firebrick is intended to be used in high heat applications to protect the steel of the stove. Soapstone is intended to be used as a heat sink to retain heat for long periods of time. You don't really want to replace one w/ the other. I have seen soapstone inside of a steel stove. Hearthstone does this on their Craftsbury. They use 4 soapstone blocks in the firebox to increase the thermal mass of the stove, but this is a very small stove to begin with and that is how it was designed.

Oh, and I am an ME.
 
It's not a matter of damaging the stove; you just end up with lower temps because the heat isn't being reflected back into the heart of the fire, is being absorbed by the higher thermal mass, and is conducted outward by the higher conductivity of the stones. The increased thermal mass, heat conductivity, and lack of reflective radiation could very well prevent the stove from reaching secondary combustion temps.


What I think would be a great experiment would be to add some refractory lining to a hearthstone stove, or replace the interior soapstone bricks with lightweight pumice firebrick. I'm quite certain this would raise temps and efficiency inside the stove, but it might make it a bit too hot for those fragile hearthstone panels.
 
cycloxer said:
Firebrick is intended to be used in high heat applications to protect the steel of the stove. Soapstone is intended to be used as a heat sink to retain heat for long periods of time. You don't really want to replace one w/ the other. I have seen soapstone inside of a steel stove. Hearthstone does this on their Craftsbury. They use 4 soapstone blocks in the firebox to increase the thermal mass of the stove, but this is a very small stove to begin with and that is how it was designed.

Oh, and I am an ME.

Isnt the Craftsbury cast iron? I never sold one of those, but I assumed it was
 
karri0n said:
It's not a matter of damaging the stove; you just end up with lower temps because the heat isn't being reflected back into the heart of the fire, is being absorbed by the higher thermal mass, and is conducted outward by the higher conductivity of the stones. The increased thermal mass, heat conductivity, and lack of reflective radiation could very well prevent the stove from reaching secondary combustion temps.


What I think would be a great experiment would be to add some refractory lining to a hearthstone stove, or replace the interior soapstone bricks with lightweight pumice firebrick. I'm quite certain this would raise temps and efficiency inside the stove, but it might make it a bit too hot for those fragile hearthstone panels.

In 25 years of selling Hearthstone I have yet to (knocking on wood) replace a damaged soapstone. I know it has happened to others in the past to other folks. I just never considered them to be "fragile"
 
I've seen several threads on here regarding cracked stones on hearthstone stoves. I'm not bashing them, as I know they make a good product, but I haven't seen anything about a cracked stone on a woodstock stove.
 
I don't think replacing firebrick with soapstone would result in any sort of nuclear meltdown of the stove per se, but it could change the required clearance to combustibles (CTC) enough to create a fire hazard. If CTC is not an issue, it could still move the sweet spot of the stove to where it affects the EPA rating and efficiency.

That said, with my stove I time the removal of ashes with the outdoor temps and subsequent need for heat. With fewer ashes in the stove, I get a lot more heat out of it. I would not dare change out the firebrick for fear of changing the CTC as my stove is a zero clearance and as such has no possible additional margin of safety. I run my blower when the stove is putting out max heat but in a power failure without the blower, it is pushing the CTC to the max.

Any major modification to a stove that affects the transfer of heat one way or the other could create a hazard. If you kept more heat in by lining the top/sides with soapstone it could raise flue temps. If you wick away heat by removing insulation, it can cause a CTC hazard. I'm pretty sure both the stove manufacturer and your insurance company would take a dim view of such mods.
 
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