Opinion on Soapstone

[Todd]

I'm saying the hotter the stones are, the more btu they have in storage. I suppose given two equal blocks of soapstone, if you bake one to 600 degrees and bake the other to 1200 degrees my guess is the hotter one has twice as much stored energy.

My point is that there is a maximum to the btu storage. The stone backed at 1200 degrees may only have 1.5 times the amount of stored energy. I don't know at what point the max is but I believe that with normal firebox temperature the maximum storage capacity is reached.

So you think once that max is reached the heat will escape up the chimney? I know what your thinking about the insulating properties but I think heat transfer will go towards the cooler living space vs the hot chimney.

 

[willmcb]

(SNIP)"I once read that soapstone will peak out at 500 no matter how much wood you put in it." (SNIP)

Sorry. This is not true. Soapstone, as well as other masonry, withstands heat much higher with ease; look at Tulikivi - all soapstone w/ firebox temps in the 2000* F range.

If there is a limiting factor to soapstone in a metal + soapstone wood stove, it is the metal, not the soapstone, that cannot take the heat w/o damage, over firing, etc. When you discuss heat qualities of soapstone when combined in a stove with steel or cast iron, you are not discussing just the soapstone.

Aye,
Marty

I knew it was not true because I have reached higher temperatures than that myself. True soapstone would remain intact longer than steel in the presence of super high temps, but given that you have a soapstone and steel stove with the same firebox temperatures the steel stove would have higher stovetop temperatures. The firebox temps of 2000 F makes me think of how soapstone is more of an insulator than a conductor. I do believe that the maximum storage of btu's can be reached in soapstone with a "normal" fire. I believe the maximum capacity is reached on the surface of the stones inside of the stove and because the heat is conducted slower (in relation to steel or cast), heat is pushed back into the firebox. Normal is defined as how the experienced stove operator operates the stove.

 

[Martin Strand III]

Another point or so...

An advantage of heating up masonry, including soapstone, is that with enough mass of masonry, you do not want hot surface temperatures on the stove as seen on a metal stove. Lower surface temperatures (around 200* F or so) produce radiant energy (heat) of lower amplitude than a hot surface. This lower amplitude energy heats objects (more dense) before heating the air (less dense than objects) which is more natural (like the warmth of the sun on a cold clear day) and healthier with less indoor weather (convection air currents circulating fried dust particles, cat dander,etc). Lower surface temperature all masonry stoves are also safer (can't burn skin quickly at 185* F).

Unfortunately, metal stoves, even with masonry or soapstone slabs on their sides and top, do not have the masonry mass to achieve this and, so, must be fired to achieve hotter surface temperatures (say, above 350* F) to heat the room.** This hotter surface radiates energy of greater amplitude which tends to heat spatially separated (compared to solid objects) air molecules as well as solid objects producing convection air currents.

**Just consider the difference in how a typical room would feel with a 300 lb rock at 185* F sitting there with you compared to an 8000 lb rock at the same temperature. The 8000 lb'er is called "thermal mass heating". Combo metal/soapstone stoves can do it only to a lesser degree.

Don't mistake my comments to put down metal/masonry combo stoves. I think they are a step in the right direction. They just don't go far enough; need much more masonry.

Aye,
Marty

 

[willmcb]

Will, that is a good looking install.

I do not think that soapstone is particular about the wood as I have detected no difference burning the same wood that we used to. Did I state that we now burn only half the amount of wood that we used to but stay warmer in the house?! The old stove was steel.

As you know Will, even standing dead wood will hold lots of moisture. Most of the time when we cut standing dead wood we season it the same as if it were green. The only exception we've had to that is with elm. If we wait until all the bark has fallen off then we can actually burn the top half of the tree right away. The bottom half though still needs much time.

It does take a lot of time to get ahead with your wood supply and I used to struggle with the same problem. But once you reach that point to where you have 3 years of wood on hand you'll never want to go back. It is a whole new ball game with wood burning when everything is right; especially the fuel. I like to ask what would happen if you put bad fuel in your car. Compare that with putting bad fuel into the stove. You just do not get the same results.

I also find it amazing that this store owner has lots of experience but yet is not really that knowledgeable. I guess it might boil down to the question: Do you have 10 years of experience or 1 year of experience 10 times?

Thanks- Well as far as fire experience I have more than ten years. I have always been a firebug. Whenever my friends couldn't get I fire going I had a blaze. I have been operating stoves as long as I can remember. I have just taken an interest in the designs and efficiencies in the past 2 or 3 years. Now I am about 2 years ahead on firewood. Standing dead wood is pretty dry in the summer when it has not rained in a couple weeks. I know that if my wood was seasoned longer it would be higher grade fuel, but when I made my comparison I was using wood of the same general quality. Don't worry I don't just burn pure hickory either. That was just for effect on the experiment. I burn a mixture of poplar, maple, oak, and hickory.

 

[ms440]

Interesting research. I have to add that I am convinced that soapstone stoves more so than steel and cast must have DRY wood. I have experienced this myself with wood that was not quite there. I can take my Mansfeild to 600 stovetop everytime I want with dry wood. With semi seasoned wood (say spring cut split and stacked in the sun) I stuggle for 450-500. The difference is huge in output. Where I live there are two distinct heating seasons, fall/spring and winter. The soapstone is incredible in the ammount of variation and personatlity it can take on. A few sticks to keep the rock cruising at 350-400 in spring/fall heats the whole house, load it up in the winter. I burn from October to April on 4 cords of wood heating very well insulated 2500 squares on the north slope of a hill without using my furnace. I guess I am saying I like soapstone.

 

[woodjack]

Will, don't let anyone talk you out of what you witnessed. . . especially the ones that make believe they're scientists. You saw what you saw. Thanks for sharing your results.

 

[Martin Strand III]

Interesting research. I have to add that I am convinced that soapstone stoves more so than steel and cast must have DRY wood. I have experienced this myself with wood that was not quite there. I can take my Mansfeild to 600 stovetop everytime I want with dry wood. With semi seasoned wood (say spring cut split and stacked in the sun) I stuggle for 450-500. The difference is huge in output. Where I live there are two distinct heating seasons, fall/spring and winter. The soapstone is incredible in the ammount of variation and personatlity it can take on. A few sticks to keep the rock cruising at 350-400 in spring/fall heats the whole house, load it up in the winter. I burn from October to April on 4 cords of wood heating very well insulated 2500 squares on the north slope of a hill without using my furnace. I guess I am saying I like soapstone.

It's widely known that

"Moisture content significantly affects burning rate.
A difference in moisture content of 10% results in a change of 20–30% in burning rate."

and that is supported in my own scientific research.

Actually, I found this tid-bit here:
http://www.fpl.fs.fed.us/documnts/pdf1992/tran92b.pdf

Aye,
Marty

 

[ms440]

No question that moisture content is a big part of it, but I am convinced that for soapstone, it is even more important to have dry wood. The stones just dont put out like a cast or steel stove can with moisture buring off. Maybe it is just my perception.

 

[Martin Strand III]

(SNIP)The stones just dont put out like a cast or steel stove can with moisture buring off. Maybe it is just my perception.

Masonry (rock, stone, marble, soapstone, etc) does not "put out" heat like metal because of the difference in heat transfer quality between to two different materials.

Cast iron conducts heat some 10X faster than soapstone.

This is simple physical properties of the materials and does not have any bearing to dry or not dry wood you burn.

Aye,
Marty

 

[Backwoods Savage]

Okay, it conducts heat faster. Question, if two stoves have the same btu's in the firebox, will a steel stove produce more btu's than the soapstone stove? If so, where exactly would that heat go from the soapstone stove? Certainly not up the chimney with the low flue temperatures we get. Simply put, I do not think you will get more btu's from steel or cast or soapstone. I think you will get the same amount of btu's. Otherwise where would the heat go? It has to go somewhere and I think it was Todd stated the heat would go toward the cooler room air. Makes sense to me.

 

[Slow1]

Okay, it conducts heat faster. Question, if two stoves have the same btu's in the firebox, will a steel stove produce more btu's than the soapstone stove? If so, where exactly would that heat go from the soapstone stove? Certainly not up the chimney with the low flue temperatures we get. Simply put, I do not think you will get more btu's from steel or cast or soapstone. I think you will get the same amount of btu's. Otherwise where would the heat go? It has to go somewhere and I think it was Todd stated the heat would go toward the cooler room air. Makes sense to me.

Perhaps the answer is in the rate at which these BTUs can be released to the room. With a steel stove perhaps they could be more rapidly released to the room than with an otherwise identical stone stove - if this were to be true then I would expect that the fuel load would be more rapidly consumed in the steel stove if all other factors (flue temp and velocity of gases up said flue) were held constant. Total energy released from two (theoretical) identical loads in the two hypothetical stoves would be the same, but one would finish first, the other would have a longer burn time.

EDIT to add -

IF the same two hypothetical stoves were to burn these identical loads at the same rate (adjust air or whatever) so that the fire burns for the same length of time and again the flue temp and gas velocity is identical, then we accept the statement that steel conducts the heat faster than the stone. I would expect the steel stove to begin releasing the heat to the room sooner than the stone (i.e. warm up faster) and perhaps reach a higher peak temperature (depending on the burn profile) than the stone. The stone version of the stove I would expect to heat up slower and not peak as high but then release the energy for a longer period of time after the fire has died out. Again - the total amount of energy released to the room I would expect to be the same.

 

[Martin Strand III]

Okay, it conducts heat faster. Question, if two stoves have the same btu's in the firebox, will a steel stove produce more btu's than the soapstone stove? If so, where exactly would that heat go from the soapstone stove? Certainly not up the chimney with the low flue temperatures we get. Simply put, I do not think you will get more btu's from steel or cast or soapstone. I think you will get the same amount of btu's. Otherwise where would the heat go? It has to go somewhere and I think it was Todd stated the heat would go toward the cooler room air. Makes sense to me.

Perhaps the answer is in the rate at which these BTUs can be released to the room. With a steel stove perhaps they could be more rapidly released to the room than with an otherwise identical stone stove - if this were to be true then I would expect that the fuel load would be more rapidly consumed in the steel stove if all other factors (flue temp and velocity of gases up said flue) were held constant. Total energy released from two (theoretical) identical loads in the two hypothetical stoves would be the same, but one would finish first, the other would have a longer burn time.

EDIT to add -

IF the same two hypothetical stoves were to burn these identical loads at the same rate (adjust air or whatever) so that the fire burns for the same length of time and again the flue temp and gas velocity is identical, then we accept the statement that steel conducts the heat faster than the stone. I would expect the steel stove to begin releasing the heat to the room sooner than the stone (i.e. warm up faster) and perhaps reach a higher peak temperature (depending on the burn profile) than the stone. The stone version of the stove I would expect to heat up slower and not peak as high but then release the energy for a longer period of time after the fire has died out. Again - the total amount of energy released to the room I would expect to be the same.

The amount of the heat that a stove actually transfers to a room depends on a number of factors:

1. Combustion efficiency.
How well the stove converts the wood to carbon dioxide and water, minimizing the production of other substances. Hotter and dryer is better.

2. Heat transfer efficiency (thermal efficiency).
How much of the firebox heat goes up the chimney into the atmosphere (stack loss) depends on the firing strategy and the thermal mass of the heater. Metal stoves and fireplace inserts with firebrick lining are designed to be clean burning but still have poor thermal efficiency because they lack a thermal mass that functions as a heat exchanger. Soapstone slabs in sides and tops of some models do not qualify as "thermal mass" heaters. They fall short on mass.
Combustion efficiency multiplied by the heat transfer efficiency, is the overall efficiency, but this term still does not fully characterize the true efficiency of a heater. An IDEAL wood heater has high combustion efficiency and "moderate" (not "high" as with an all metal stove) heat transfer efficiency. Soapstone, or other masonry, is sometimes added to an otherwise all metal stove to "moderate" the heat transfer efficiency.

3. Linearity of output.
For clean combustion, wood requires a brisk, hot fire which results in short burn times. If the heater has no storage capacity, as in metal and metal/soapstone combos, the fire must be damped, otherwise all the heat is transferred into the room during the burn time not to mention over firing the stove or losing the heat up the chimney. Thus, the room becomes overheated while the fire is burning and under heated after the fire has died down. An overheated room loses more heat to the environment because of the higher temperature differential between the room air and the outdoor air.

4. Partial charge efficiency.
Most metal and metal/soapstone stoves do not handle small fuel charges efficiently because high temperatures are needed to obtain non-smoldering combustion. In the milder days of the heating season when only a partial charge is required, burning smaller fuel charges is the idea but some stoves, simply put, are not designed to do this.

In short, soapstone paneled metal framed stoves act like a mini-heat bank but do not have the mass of a thermal mass heater. They warm up slower, bank some heat and cool down slower than their all metal cousins. Neither fire box nor stove can take the full bore full air supply to burn a full fuel load without dampening.

This help?

Aye,
Marty

 

[Backwoods Savage]

Nope. No help at all Marty. I know you mean well but we just try to keep things simple so more folks can or will understand better. Therefore, I say if a steel stove produces 30,000 btu's and a stone stove produces 30,000 btus, the heat is the same. It is true that some heat will be stored in the rock for later transmission to the cool room but once the rock reaches a certain temperature, then all the heat is being transferred the same as it is in the steel stove. You can no hide the btu's. Yes, the efficiency of the stove matters but if the stoves are the same efficiency then you get exactly the same amount of btus in each stove.

 

[DanCorcoran]

If you're correct (and I think you probably are), the areas under the 3 curves on the chart should be equal and should represent the total BTUs consumed:


http://www.hearthstonestoves.com/stove-guide/Why-soapstone

 

[Martin Strand III]

Nope. No help at all Marty. I know you mean well but we just try to keep things simple so more folks can or will understand better. Therefore, I say if a steel stove produces 30,000 btu's and a stone stove produces 30,000 btus, the heat is the same. It is true that some heat will be stored in the rock for later transmission to the cool room but once the rock reaches a certain temperature, then all the heat is being transferred the same as it is in the steel stove. You can no hide the btu's. Yes, the efficiency of the stove matters but if the stoves are the same efficiency then you get exactly the same amount of btus in each stove.

You are correct. It is simple.

Apply the same heat (BTU's) to a 5 lb soapstone chunk and a 5 lb chunk of cast iron/steel.
They absorb the heat at different rates and release it at different rates. Stone slower, metal faster.
After all is said and done, the heat absorbed equals the heat released.
The difference is time. Stone slower (longer time), metal faster (shorter time).

Aye,
Marty

 

[willmcb]

If you're correct (and I think you probably are), the areas under the 3 curves on the chart should be equal and should represent the total BTUs consumed:


http://www.hearthstonestoves.com/stove-guide/Why-soapstone

This chart is going to be biased. Hearthstone is mainly a soapstone producer. So you can expect the chart to be skewed, they want to sell their product. You can't rely on information that is advertising stoves. It hard to rely on anything found on the internet. To truly figure things out you have to do it on your own.

 

[Backwoods Savage]

Nope. No help at all Marty. I know you mean well but we just try to keep things simple so more folks can or will understand better. Therefore, I say if a steel stove produces 30,000 btu's and a stone stove produces 30,000 btus, the heat is the same. It is true that some heat will be stored in the rock for later transmission to the cool room but once the rock reaches a certain temperature, then all the heat is being transferred the same as it is in the steel stove. You can no hide the btu's. Yes, the efficiency of the stove matters but if the stoves are the same efficiency then you get exactly the same amount of btus in each stove.

You are correct. It is simple.

Apply the same heat (BTU's) to a 5 lb soapstone chunk and a 5 lb chunk of cast iron/steel.
They absorb the heat at different rates and release it at different rates. Stone slower, metal faster.
After all is said and done, the heat absorbed equals the heat released.
The difference is time. Stone slower (longer time), metal faster (shorter time).

Aye,
Marty

Now you are talking Marty. Thanks.

 

[willmcb]

Nope. No help at all Marty. I know you mean well but we just try to keep things simple so more folks can or will understand better. Therefore, I say if a steel stove produces 30,000 btu and a stone stove produces 30,000 btu, the heat is the same. It is true that some heat will be stored in the rock for later transmission to the cool room but once the rock reaches a certain temperature, then all the heat is being transferred the same as it is in the steel stove. You can no hide the btu. Yes, the efficiency of the stove matters but if the stoves are the same efficiency then you get exactly the same amount of btu in each stove.

Yes it would be true if both the stoves released 30,000 btu, that would be an equal measure of heat. But the fact is stove btu ratings are do not reflect how much heat is released. The ratings depend upon the firebox size and how much wood you can put in them. While comparing efficiencies of Quadrafire and Hearthstone stoves I noticed that the Quadrafire stoves generally had higher efficiencies by 1-2 percent and the design behind these stoves are very similar. But this doesn't mean much to me. The thing is efficiency percentages based on the EPA tests come from tests of extraction efficiency rather than heat transfer efficiency (this came from my research of EPA stove testing in an interview). This measure is a relation of the weight of ashes left in the firebox to the weight of the load put in. The EPA is not so concerned with heat transfer efficiency. They are concerned with air quality and in turn their tests deal with particulate matter emission. The stove companies can say what they want when it comes to heating qualities.

 

[willmcb]

Nope. No help at all Marty. I know you mean well but we just try to keep things simple so more folks can or will understand better. Therefore, I say if a steel stove produces 30,000 btu's and a stone stove produces 30,000 btus, the heat is the same. It is true that some heat will be stored in the rock for later transmission to the cool room but once the rock reaches a certain temperature, then all the heat is being transferred the same as it is in the steel stove. You can no hide the btu's. Yes, the efficiency of the stove matters but if the stoves are the same efficiency then you get exactly the same amount of btus in each stove.

You are correct. It is simple.

Apply the same heat (BTU's) to a 5 lb soapstone chunk and a 5 lb chunk of cast iron/steel.
They absorb the heat at different rates and release it at different rates. Stone slower, metal faster.
After all is said and done, the heat absorbed equals the heat released.
The difference is time. Stone slower (longer time), metal faster (shorter time).

Aye,
Marty

Now you are talking Marty. Thanks.

You can apply the same amount of heat and get a different amount of heat stored in each material. This is true especially in a wood stove where air is constantly flowing in and out. Yes, time is the variable that makes the difference. That goes back to my house theory. The quicker transfer absorption and transfer rate of the metals makes them superior when it comes to heating efficiency. Common sense says that two stoves made from different materials of the exact same design would transfer a different amount of heat in the presence of equal air and wood input because heat absorption rates are different while the air flow out is constant. Marty pointed out that cast iron transfers heat 10x faster than soapstone. That is why the heat coming off steel or cast iron at a specific surface temperature is much more penetrating than it is coming off soapstone. So you can assume at a given surface temperature steel or cast iron would actually be putting out more heat than soapstone. Dennis it was incorrect to say that once the soapstone reaches a certain point it transfers heat just the same as steel. Where the transfer rate varies in soapstone it will also vary proportionately in steel.

 

[willmcb]

I hate to sound like I am criticising soapstone. I am but only in one aspect. Soapstone stoves are great. They have many benefits. I just don't think they have the capability to transfer as much heat. Where they can't transfer as much heat in the short run they will surely make up for it in the long run. Soapstone is a much more durable material. On top of that I find soapstone stoves to be the best-looking. That is why the Mansfield rather than the Oakwood is burning in my living room right now.

 

[yanksforever]

Asking the opinion of Soapstone is like asking do you like Democrat or Republican..Catholic or Jews. Very volitle
subject. And then again you have some that can't afford them and just put them down for that reason. The reason I like it is
because it doesn't burn you out of the room the stove is in. And better looking than most steel stoves any day. IMHO

 

[willmcb]

Again I am a happy soapstone owner. Don't take this as me putting them down. I just examine all types of stove and I see their pro's and con's. In the end it all just depends on which benefits you prefer to have. So you can see once more:

 

[woodjack]

Nope. No help at all Marty. I know you mean well but we just try to keep things simple so more folks can or will understand better. Therefore, I say if a steel stove produces 30,000 btu's and a stone stove produces 30,000 btus, the heat is the same. It is true that some heat will be stored in the rock for later transmission to the cool room but once the rock reaches a certain temperature, then all the heat is being transferred the same as it is in the steel stove. You can no hide the btu's. Yes, the efficiency of the stove matters but if the stoves are the same efficiency then you get exactly the same amount of btus in each stove.

That makes perfect sense. So, which is better to heat a house? The answer, I think, depends on the house. For a well insulated house, I'd think a soapstone stove would be perfect, providing a steady comfortable heat. For a house with a leaky envelope (like mine) I think a steel stove is probably more effective. I need heat fast, and for the stove to get very hot, plus I need to feed the stove often to maintain a high temp.

 

[REF1]

After reading all of this I have to agree with woodjack to some degree. Depends on the house. This is my second soapstone. I've had the Hearthstone 700 pounder back in the 90s and now have a Homestead. I had a super-insulated 3000 sq' new house in the 90s. This house is an older one, with just 3.5" of insulation in the walls, crawl space floor, and in the attic walls. The house is only 1300 sq'. Right now, with the stove running at 550 for about an 2 hours now, it's only 58 in here. Nice and warm upstairs, to be sure, but 20' feet from the stove it's pretty cool. Takes a long time for soaps to heat things up.

The soapstone heat 'feels' even compared to steel stoves I have had in the past. I haven't owned a full cast iron. But a 3' steel/cast iron Cat Elm proved the best overall heat for the 3000' house. The soap heated well but still killed us in the Spring. Too much heat. Too long to heat up. In this house, the Homestead takes forever to heat the downstairs. The fact that soaps hold heat does not make it appreciable heat. This morning the stove was very warm. I couldn't hold my hand on it. But 6" from the stove no heat could be felt. I am getting a steel stove to replace it because I want fast heat. It's also going to be convection because I'd rather have the heated air than fully radiant. A bigger soap might do better for really cold days in this house, but than it would cook us out for fall and spring. Steel will give this house a needed fast warm-up and then we can cruise while at work when the temp hits 40-50 here at this time of year. I'd rather have a fast heat and long burn in this house.

I have definitely seen this soap REQUIRES a full load of smaller wood to perform at its best. It doesn't like a half load nor large splits. My highest temps are full loads of smaller splits and branches. That may be the case with all EPAs, I don't know.

 

[BrowningBAR]

I have definitely seen this soap REQUIRES a full load of smaller wood to perform at its best. It doesn't like a half load nor large splits. My highest temps are full loads of smaller splits and branches. That may be the case with all EPAs, I don't know.

This baffles the hell out of me as I have seen and used soapstone stoves with one or two splits and they still shoot off a nice load of heat.