Plate steel vs cast iron vs stone

[karri0n]

Ok, so I've heard conflicting reports on this. Conventional wisdom as well as my own knowledge would tell me it's a matter of heat transmission, radiance, and retention. If we were looking for the highest possible amount of heat transmission, stoves would be made of copper. This obviously is not the case. If we were looking for the highest possible amount of radiance, stoves would be aluminum. Another advantage would be the stoves would be far lighter if this were the case. Extremes in any category are obviously not what we are looking for. I'm uncertain of the thermal properties of soapstone compared to cast iron or plate steel, but I would imagine that it retains heat the most out of the 3 materials. I would also be confident in taking a guess to the reason for soapstone as opposed to, say, granite, would be that soapstone is a lot more soft and workable than a hard, brittle stone. Now, on to the actual question.

I am fairly certain that steel is a better transmitter of heat than cast iron, and therefore heats up faster, but also cools down faster. This would mean that cast iron retains heat much better than plate steel can. According to some reports, however, this is not the case. Some say that the cast iron not only refuses to transmit heat well, but that it heats up unevenly and even cools down faster than a similar steel stove. This seems counter-intuitive, as I cook with both cast iron and steel pans and I know that my cast iron has a much more even heat, as well as better heat retention, than any steel pan, even on an uneven heat source. The steel pans tend to get hot and cool spots even with a relatively much more even heat source.

Are these conflicting reports based on user bias, improper stove design/setup, or just based on users not getting their exact expectations out of their stove? Also, has anyone owned all three, or owned both a metal and stone stove, and, if so, did you notice any major difference in heat retention or transmission between the different materials?

Personally, I don't think I would purchase a steel stove. I've always been fond of the look and feel of cast iron, and employ it in my decor as well as cooking. I am, however, very interested in the soapstone stoves, as they seem to me like they would have the best heat retention of all, and therefore continue to stay warm for quite some time after the stove has burned down to coals. Any insight or discussion on this would be great.

 

[thechimneysweep]

I've burned all three, and my experience agrees with this chart from Hearthstone:

It is my understanding that plate steel and cast iron are both about 86% heat transfer efficent. The difference in heating qualities between those two materials seem to be mostly about weight and thickness (cast iron stoves tend to be thicker and heavier than plate steel stoves, and the difference is due to the resulting extra thermal mass).

 

[karri0n]

Very interesting. Thanks for your reply!

 

[fossil]

That's pretty interesting...Hearthstone actually trademarked the neologism "Heatlife". I wonder why nobody's trademarked "Burntime", or some clever variant thereof. Rick

 

[jqgs214]

Actually the TM symbol does not mean its registered only that they have intention to and may be financially compensated, if Hearthstone is deemed to have lost money by the use of the word by another user. If another company uses that phrase and Hearthstone had it registered, a circled r afterward, then they would need prior authorization and compensation to use the word.

In other words WXMAN tm is now trade marked but if you use it I would need to prove financial loss to get compensated.

 

[Jags]

I've got a trademark on "gription" :coolsmile:

Yep, I think that mass has a bunch to do with the characteristics of each type of stove. Lets face it, if you have 300 pounds of plate steel heated to 600F and 600 pounds of cast heated to 600F there is a HUGE difference in energy there. Of course there are the differences in the materials themselves, but mass has a whole bunch to do with it.

 

[fossil]

Mass has everything to do with it. Keep in mind, though, that it's not just the mass of the space heater that's involved in the overall system. The mass of everything surrounding it comes into play. After a few hours' burning, the room and everything in it, and the structure inside the insulation envelope have all been warmed substantially by the radiant and convective energy produced by the stove. Even after the stove has completed a burn cycle and is well into cooling down, the room will still feel warm, because the surroundings are re-radiating the heat they absorbed while the stove was hot. I think proper sizing of the stove to the task, and attention paid to insulation and overall heat efficiency of the structure might be more important to the performance of the system than the material from which the appliance is constructed. Rick

 

[Highbeam]

"Also, has anyone owned all three, or owned both a metal and stone stove, and, if so, did you notice any major difference in heat retention or transmission between the different materials?

Personally, I don’t think I would purchase a steel stove. I’ve always been fond of the look and feel of cast iron, and employ it in my decor as well as cooking. I am, however, very interested in the soapstone stoves, as they seem to me like they would have the best heat retention of all, and therefore continue to stay warm for quite some time after the stove has burned down to coals. Any insight or discussion on this would be great."

I owned both a modern large plate steel insert and now a soapstone freestander. I agree with the chart. When the fire went out in the plate stove, the heat went away. Not so with the stone. Notice also the peak temps. I would rather sit by the 500 degree stove then next to a 900 degree stove.

 

[VTSR5]

Something is fishy here. Note that the areas under the curves are not really equal. The soapstone stove seems to have "magically" created energy somehow. Hey, wait a second...somebody get me the White House. I think I have solved the energy crisis!

 

[Jags]

Something is fishy here. Note that the areas under the curves are not really equal.

??? I'm lost.

 

[johnnywarm]

Something is fishy here. Note that the areas under the curves are not really equal.

??? I'm lost.

Same here

 

[fossil]

We don't really know anything about that graph...how the data was collected, what stoves/fuels were used...not much of anything. What we do know is that Hearthstone published it. Doesn't really matter. What matters is that the OP said, "Personally, I don’t think I would purchase a steel stove. I’ve always been fond of the look and feel of cast iron, and employ it in my decor as well as cooking. I am, however, very interested in the soapstone stoves, as they seem to me like they would have the best heat retention of all, and therefore continue to stay warm for quite some time after the stove has burned down to coals." I can't think of a better reason to make my choice between the available appliance materials than my personal preference. After that, it's all about the installation and how it's operated, and the overall system into which it's incorporated. Fuel in, heat out. Rick

 

[fossil]

...Something is fishy here. Note that the areas under the curves are not really equal...

I'm totally amazed by how quickly you derived the equations for those curves and integrated each of them! Nice work. %-P Rick

 

[Jags]

Rick - quit confusing me using sensible logic.

Edit: The OP can't really know what she wants yet, we haven't told her yet :lol:

 

[VTSR5]

??? I'm lost.

The line of each graph plots the temperature of a stove at different points in time. The area under each line therefore could be taken as an approximation of the total energy output of each stove. For a fair comparison between different stoves, you would expect the stoves to be loaded with equal quantities of wood (energy), and therefore you would expect the area under each graph (also energy) to be about the same. Indeed, the steel and iron stoves are fairly compared to each other because the areas, though differently shaped, are about the same. But the area under the green line, representing the soapstone stove, is significantly larger than the other two areas, suggesting that stove released more energy. No one has ever claimed that a soapstone stove is more efficient at converting wood to heat than is a steel or iron stove, though that is one implication of these graphs. I found that humorous, so I poked a little fun at it.

 

[Todd]

I wonder why the old Hearthstone literature had the soapstone curve topped up to 600 and now it's down to 500? Maybe they stretched out the line more? Those damned soapstone guys are trying to cheat! ;-P

 

[VTSR5]

I'm totally amazed by how quickly you derived the equations for those curves and integrated each of them! Nice work. %-P Rick

Just eyeballin' it, as usual. :cheese:

 

[Todd]

Actually the graph is pretty close to my 12 hour burn and temps, but I top out higher. Everyone should draw their own graphs and report back for a real world comparison.

 

[Highbeam]

Also the soapstone never cools off, just runs at 200 forever. I can tell you that the stove can take hours to get from 200 to zero. Tough to eyeball but I agree that the areas should be the same under the curves.

Let's just call it a qualitative graph.

 

[fossil]

Asymptotic to ambient. I like highbeam's suggestion...I think the graph is qualitative, and probably fairly representative of the behavior of stoves of different materials over time. BUT...and it's a big but I've got here...this thing is showing stove temperature, not the total system (room) temperature. There are many other factors at play in how a stove is going to perform to provide the heat desired in a given installation. I go back to stove sizing, placement, and insulative properties of the structure. Rick

 

[karri0n]

Rick - quit confusing me using sensible logic.

Edit: The OP can't really know what she wants yet, we haven't told her yet :lol:

Is it because I used the word "decor"? 23/M/CT here.

I understand now what you mean by area, as in X axis x Y axis. However, with the soapstone, the reason the area would be higher is not necessarily(not ruling it out) due to hearthstone fudging the numbers, but because the ambient temp in the room is not likely zero, and therefore the heat loss would slow as the stove cooled. The graph is, after all, meant to show that a hearthstone stove retains and radiates the heat in a more efficient manner than an Iron or steel stove.

 

[Islander08]

One of the factors that might effect the area under the curve in that comparison is how much of the energy was lost up the chimney. If the comparison was between two clunky traditional steel and cast iron stoves vs a highly efficient soapstone one, perhaps the curves make more sense.

 

[BJ64]

One of the factors that might effect the area under the curve in that comparison is how much of the energy was lost up the chimney. If the comparison was between two clunky traditional steel and cast iron stoves vs a highly efficient soapstone one, perhaps the curves make more sense.

All I know is the chart makes my barrel stove out in the shop look like hammered crap. Like you guys said, it is all about thermal mass.

I figure some of these old rotted off locust fence post must be 60 years old. They are still solid and if they were not too short I would use them again as fence post. They served so well for so long, it is a shame to burn them, but 6 of them in that shop stove is all you want - for 30 minuets.

 

[BrotherBart]

Big honkin heavy steel stoves rule! 500 pounds of steel and bricks does that 200 degrees for a long time trick too. Stick that sucker in a brick fireplace and the bricks get to pay their way too. :coolgrin:

 

[Todd]

BB hit on another good point. You can also get some thermal mass from a nearby brick or stone hearth and fireplace.