Soapstone Stoves vs Everything Else?

[leeave96]

I had an interesting experience with my fine Woodstock Keystone over the weekend. When I bought the stove, I also bought additional soapstones for the stove top. The soapstones on the stove from the factory are recessed in some decorative (and I am sure structural) cast iron - so you don't really have a smooth/level surface for a large pot or pan to set on. Looks great, but I thought I'd like to have a smooth flat surface.

Fast forward to this weekend. I finally got around to putting the stones on the stove top and found the surface temperature of the new stones to be anywhere from 60 to 100 degrees cooler! I put them on and took them off to have an apples to apples comparison with regard to the temperatures. It was like the additional stones served more as an insulating blanket than radiant heaters.

In addition, the front of my stove is a cast iron frame, wth a very large window and a small strip of soapstone across the bottom. The right and left sides are soapstone with some cast iron structure.

The front of the stove radiates far more heat than the sides.

With the new stones removed from the top of the stove, the top radiated much more heat too.

So my question is this - from a heating stand point, is soapstone a gimmic? If the point of a stove to impart heat into a space, does the soapstone impede the full heat potential of a stove?

I do realize that the soapstone does eliminate the spikes when firing the stove because it absorbes the heat - like an insulator and releases it slowly into the room as the stove cools, but if you have a well insulated house (which I don't), would it be better to hold the heat in the room rather than in the stone?

Don't get me wrong, I love my fine Keystone and would make the same choice again, but I think that if you are looking for max heat output, a soapstone stove may not be the best choice. I do like the regulation of the heating spikes and I really like the looks of the soapstone stoves too.

Anyone out there who have used both cast iron and/or steel plate stoves would share their first hand experiences? I can only comment on my Keystone and the old smoke dragons of my past.

Just courious - not trying to stir the pot!

Thanks,
Bill

 

[Dakotas Dad]

My guess, not totally uneducated..

You added thermal mass. takes heat to "fill it". The more mass you have the lower the temperature you will be able to bring it up to with the same bTu's. Also, on the level of contact, the stones don't really touch very well, so there is an air gap insulator. If you mess with building computers, look up "thermal paste" the backside of a cpu and the underside of a heat sink sure seem smooth, until you want heat to jump the gap, then you use thermal paste to improve heat transfer efficiency by a huge amount.

Look up masonry heaters, or Russian stoves, etc. Instead of several hundred pounds of mass they have a couple, to many, TONS. They NEVER get near the surface temperature you do with your stove. Many of them only get around 90-110°F but it takes a LONG time for that much stone (thermal mass) to give off all it's heat. I dated a girl in Germany years ago who's family had one, I loved it. Even right during/after a fire you could lean right against it. Just slow low steady warmth.

rambled a bit there.. sorry.

 

[Fsappo]

For raw blistering heat, I'll sell someone a steel stove. For extra long heat life and a more steady heat along with excellent quality and looks, I do a soapstone, for kinda the reasons that Dakotas dad, chaser of german women, mentioned.

 

[YankeeFarmer]

I'm a brand new soapstone owner/user. We replaced our 18 year old VC Resolute Acclaim with a Hearthstone Heritage. just had our first "real" fire this past weekend, after 2 break-in fires last weekend. (I was away all week and my wife will tend the stove, but won't build a fire.) So my experience with this stove should be taken with with the knowledge that I'm still learning how best to operate it. Also, the Heritage is a larger stove than our Resolute Acclaim. There is no shortage of heat from the Heritage!

Radiant heat through the large front glass window is strong. True, the soapstone on the top hasn't approached the high temps i used to see on the cast iron griddle of the older stove. But I can have a very hot fire in the stove without the high stack temps I was running with the Resolute Acclaim. (I replaced the RA because i couldn't put it into high efficiency mode without it puffing and smoking. After reading about the cost and frequency of rebuilds, and considering my wife's desire for a stove that was attractive on the back side as well as the front and sides, the Heritage made sense.) I think the larger surface area of the new stove makes up for the slightly lower surface temps. The Heritage seems to be much more efficient, although a good chunk of that is likely due to the degraded condition of the old stove.

It seems to make sense that two stoves of equal size and surface area, one being soapstone and one steel or iron, the soapstone might put out slightly less heat.

Jerry

 

[branchburner]

I finally got around to putting the stones on the stove top and found the surface temperature of the new stones to be anywhere from 60 to 100 degrees cooler! I put them on and took them off to have an apples to apples comparison with regard to the temperatures. It was like the additional stones served more as an insulating blanket than radiant heaters.

I have a few 10x16 3/4" soapstone slabs I can put on the top of my cast iron stove. They seem to reach nearly the same temps, but take a LONG time to do so. It is hard to have an apples to apples comparison because to account for the lag time, you also have to take into account the length and stages of the burn cycle. If you keep adding wood and extend the hot burn you will eventually get them up there in temp.

All you are doing is making your stove thicker, therefore slower. Not good if you want to quickly heat all the air in your house. But you are not losing heat, just making it more usable as radiant heat over a longer time period.

 

[Slow1]

I have the 'cook stones' for my FV as well and also have noted the reduced surface temperatures. Now what to do with the data and what conclusions to draw from it...

First I don't believe it means that soapstone stoves are less efficient at getting heat from the fire into the room. Just look at the reality of the flue temps and burn rates - the heat has to be going somewhere and if it isn't up the flue where is it going eh? Then there are the lab tests that seem to indicate some support for at least as good efficiency (depending on if you like those definitions of efficiency).

So then what does it tell you when you put stone on top of a 500* stove top and the stone only measures 400*? Well, my conclusion is that the stone on top simply isn't getting heated efficiently. From my experience trying to cool chips on computers by attaching a heat sink (the stone on top playing the role of the heat sink here) any air gaps between the surface to be cooled and the heat sink can SERIOUSLY reduce the efficiency of thermal transfer. Thus the need for thermal 'grease' to fill the gap as well as very flat surfaces (polished in some cases) as well as tight clips to squeeze it all together. Not exactly the conditions between my cook stone and surface of the stove. There is an air gap there so direct conductive transfer isn't really happening for most of the surface thus heat has to rely on convection (via the trapped air) and radiation between the stones. Not very effective and I suspect enough to explain the drop in temperature.

I do wonder what effect running with the stones in place on the stove has on the overall efficiency of the stove - does it reduce the overall ability of the stove to get heat out or will the heat find other ways into the room? I don't know. I was thinking of trying to experiment with the stones on and off and check the flue temps but never got around to it as I believe it would require a large number of samples in order to normalize for expected variations in temps caused by different burn cycles/drafts/room temperatures etc. I ended up deciding to only put the stones on top when actually using them to protect the top (i.e. cooking) rather than all the time just in case it reduced overall heating efficiency.

 

[Backwoods Savage]

Good ideas Slow.

Even Woodstock will tell you to expect at least a 50 degree difference.

I just checked our stove that has the boot driers on top of the stove. There is about 100 degrees difference in the top of the driers compared with the stove top measured in the center of the stove. I have noticed from time to time when checking that I can expect from 50-100 degrees in difference.

As Slow1 mentioned, the heat has to go somewhere and in this case it is my bet that if you cover the top of the stove, more heat will come through the sides and front/back of the stove. So as he mentioned, the extra stone on top is to be used for protection and not to increase the heating effect.


For those interested, you can get the boot driers and glove driers direct from Woodstock. These things are great for drying things but also for heating up a pair of gloves before putting them on. I use them when cutting wood during the winter. I wrap up a pair of gloves with the driers in them. When my hands get cold, I switch gloves. Nice!

 

[Adios Pantalones]

First- "Heat" and "temperature" are not the same thing. Heat refers to total energy. Soapstone sucks up a lot of heat (water sucks up even more per pound), it takes a lot of heat to raise the temp, but it stores that heat and releases it longer.

Cast iron is more like a fire for cooking steaks- hotter and faster. Soapstone is more like BBQ- low and slow (that is the tempo).

So- if you want heat quick and hot- I'd forego soapstone. If you want heat longer, steadier, but a bit lower- go with soapstone.

 

[Renovation]

I do wonder what effect running with the stones in place on the stove has on the overall efficiency of the stove - does it reduce the overall ability of the stove to get heat out or will the heat find other ways into the room?

Hi Slow,

Your analysis makes sense to me. My best-guess answer to your question is "both"--less heat goes out the top because the soapstone not only holds heat but also insulates, more goes out other ways, including up the flue. Is it a meaningful loss of efficiency, considering someone said less of the heat goes out the top already? I'd guess not, but that's up to the user to decide.

To answer the original poster's question if soapstone is inefficient, because adding it to a stone reduces efficiency, my answer is "no". A stove is a system, with materials, dimensions, design, etc. all interacting. A good stove's design allows all those factors to interact to produce an efficient result, and a soapstone stove can be just as efficient as any other if designed correctly.

After market add-ons affect the design balance, as you have seen. Saying soapstone is an inefficient technology because a stove is less efficient with an extra piece on top is like saying gas engines are inefficient technology because a car gets lower mileage after putting a second gas engine in the trunk.

 

[Adios Pantalones]

Again- it takes more heat to get a given temperature rise in soapstone, but that energy is still there. It takes longer to transfer out because the soapstone has a higher "specific heat capacity". It all comes out anyway, just slower.

It's like when you are done cooking in your oven- if you open the door, the heat comes out quick. Leave the door closed- the heat comes out anyway just slower. It's the same amount of heat, just distributed differently.

The coupling of stove top to the soapstone may or may not introduce an inefficiency that's measurable. I dunno.

 

[DanCorcoran]

The Shelburne woodstove is in my cabin. Our house here in Richmond (built 1921) has hot-water cast-iron radiators. They only get up around 120 degrees, but the heat is wonderful! It's a warm glow that doesn't fluctuate nearly as much as forced air heat. The house always feels cozy, and with radiators in every room, there's that glow throughout the house.

I think the effect is much like soapstone or the German stoves: lower temperatures at the appliance that's radiating the heat, but the mass keeps it coming in a steady flow.

 

[Renovation]

Again- it takes more heat to get a given temperature rise in soapstone, but that energy is still there. It takes longer to transfer out because the soapstone has a higher "specific heat capacity". It all comes out anyway, just slower.

In case it is interesting, and at risk of being a PITA, I'll point out that adding extra 3rd-party soapstone to a surface adds not only thermal mass, but insulation too, that the stove was not designed for. This means that not as much heat will flow through that path. The effect could well be minor, but I wanted to point it out.

 

[cptoneleg]

I wanted a soapstone stove but changed my mind, made asoapstone hearth instead, and thats apiece of soapstone under the kettle, keeps it from boiling over on my stove. The stuff really does hold the heat. The only place it gets real hot is directly behind the stove.

 

[Lynch]

i have read and understand what everyone is saying here but, doesnt the soapstone's heat last 1-2 hours if not more even after the fire has gone out ???

now i know with my dads wood stoves (cast iron) once the fire goes out the stove is pretty much cooled off by then . thats even with some coals left from the night befor.



so not having a soapstone i would think it sounds like a better stove in some cases. lower temps on surface but last longer. and wont drive you out if you really put the wood to'er

just my opion of what i have read

 

[shawneyboy]

i have read and understand what everyone is saying here but, doesnt the soapstone's heat last 1-2 hours if not more even after the fire has gone out ???

now i know with my dads wood stoves (cast iron) once the fire goes out the stove is pretty much cooled off by then . thats even with some coals left from the night befor.



so not having a soapstone i would think it sounds like a better stove in some cases. lower temps on surface but last longer. and wont drive you out if you really put the wood to'er

just my opion of what i have read

That is the advantage to soapstone. Once you get the puppy up to temp, even as the fire dies down the stone is still hot. It retains and releases the energy , in the form of heat, over a longer period of time. Also it gives off what some call a softer heat, again, it is releasing the heat slower and steadier, as opposed to the extreme peaks and valleys that some stove can give you.

 

[Bigg_Redd]

I had an interesting experience with my fine Woodstock Keystone over the weekend. When I bought the stove, I also bought additional soapstones for the stove top. The soapstones on the stove from the factory are recessed in some decorative (and I am sure structural) cast iron - so you don't really have a smooth/level surface for a large pot or pan to set on. Looks great, but I thought I'd like to have a smooth flat surface.

Fast forward to this weekend. I finally got around to putting the stones on the stove top and found the surface temperature of the new stones to be anywhere from 60 to 100 degrees cooler! I put them on and took them off to have an apples to apples comparison with regard to the temperatures. It was like the additional stones served more as an insulating blanket than radiant heaters.

In addition, the front of my stove is a cast iron frame, wth a very large window and a small strip of soapstone across the bottom. The right and left sides are soapstone with some cast iron structure.

The front of the stove radiates far more heat than the sides.

With the new stones removed from the top of the stove, the top radiated much more heat too.

So my question is this - from a heating stand point, is soapstone a gimmic? If the point of a stove to impart heat into a space, does the soapstone impede the full heat potential of a stove?

I do realize that the soapstone does eliminate the spikes when firing the stove because it absorbes the heat - like an insulator and releases it slowly into the room as the stove cools, but if you have a well insulated house (which I don't), would it be better to hold the heat in the room rather than in the stone?

Don't get me wrong, I love my fine Keystone and would make the same choice again, but I think that if you are looking for max heat output, a soapstone stove may not be the best choice. I do like the regulation of the heating spikes and I really like the looks of the soapstone stoves too.

Anyone out there who have used both cast iron and/or steel plate stoves would share their first hand experiences? I can only comment on my Keystone and the old smoke dragons of my past.

Just courious - not trying to stir the pot!

Thanks,
Bill

I wouldn't use the term "gimmick" I would use the words "unsightly fad" or "huge rip off"

 

[ddddddden]

It may just be wording, but I think of soapstone as a reservoir or buffer rather than an insulator. Mr. Pantalones is on the money. The relevant characteristc is the specific heat of the material. The specific heat of soapstone is approx double that of iron/steel. Keeping it simple, a 500-lb piece of soapstone stores heat like a 1000-lb piece of iron does. There are some other factors. . .A 1000-lb stove would probably have a larger surface area, so it would transfer heat more quickly than a 500-lb stove. . .

 

[ddddddden]

It may just be wording, but I think of soapstone as a reservoir or buffer rather than an insulator. Mr. Pantalones is on the money. The relevant characteristc is the specific heat of the material. The specific heat of soapstone is approx double that of iron/steel. Keeping it simple, a 500-lb piece of soapstone stores heat like a 1000-lb piece of iron does. There are some other factors. . .A 1000-lb stove would probably have a larger surface area, so it would transfer heat more quickly than a 500-lb stove. . .

 

[pinewoodburner]

Just reloaded my Fireview. Top tempature had gotten down to 214 degrees. After 10 minutes, the side soapstove is at 240 and the cast iron door is at 468 after 10 minutes. Door also cools down alot quicker than the soapstone.

 

[Slow1]

Just reloaded my Fireview. Top tempature had gotten down to 214 degrees. After 10 minutes, the side soapstove is at 240 and the cast iron door is at 468 after 10 minutes. Door also cools down alot quicker than the soapstone.

I lit mine about an hour and a half ago - cold stove as it was strangely warm here last night and today. Predicted low of 25 (from high of 49) tonight so decided to go ahead and light it up and set up for a nice long low burn... have to use that cat eh?

Anyway - temps right now are:

Top - 380 (no cook stone, center stone)
Top - 270 (side with cook stone - measured on edges as there is a large 4 gallon stew pot of water that was room temp sitting in middle of stone, calculate the thermal mass of that eh?)
Door - 420
Other side (stone) - 320
Glass - 465
Pipe (18" above stove, single wall surface) - 190

I imagine that it is pretty much stabilized for the burn and will hold these temps for quite a time - although the surface temp will most likely go up a bit sometime (always does for some reason). In the morning I'll be surprised if the surface is below 250.

Bottom line in my opinion is that the overall design of the stove is more important than the actual materials. Put another way - I don't believe that the materials make the stove, rather a well designed stove makes the most of the materials it is made of to deliver on some consumer's set of needs/desires. Take a BK - they are a steel stove but I don't think folks who own them complain of being blasted out of the room from intense heat when they don't want to. Instead they report being able to get steady heat either low or high as they need/desire. The stove is designed to work that way. If you want to feel like you are standing in front of a blast furnace with the doors open then there are stoves that can give you what you want - thank goodness for the free market options we have eh?

 

[Renovation]

It may just be wording, but I think of soapstone as a reservoir or buffer rather than an insulator. Mr. Pantalones is on the money. The relevant characteristc is the specific heat of the material. The specific heat of soapstone is approx double that of iron/steel. Keeping it simple, a 500-lb piece of soapstone stores heat like a 1000-lb piece of iron does. There are some other factors. . .A 1000-lb stove would probably have a larger surface area, so it would transfer heat more quickly than a 500-lb stove. . .

My point, minor as it may be, is that any material has both characteristics--specific heat, and conductivity. Soapstone is coveted for its specific heat, and manufacturers take it's conductivity (insulation) into account when designing stoves, so it's not an issue. Adding soapstone after the fact increases both thermal mass and insulation, and may or may not affect the stove's output and efficiency, since it was not designed for the added soapstone.

I am not mentioning this to criticize soapstone as a material, for I personally would love to have a soapstone stove, all else being equal. I'm criticizing making conclusions about a design feature by slapping it on an existing stove--in this case, adding soapstone to an existing stove affects it, small as those effects may be.

To answer the main question of the OP, I think soapstone is not a gimmick, but a useful technology, like catalysts, thermal (non-cat) secondaries, thermostats, firebricks, welded steel, cast iron, shields, and blowers. Soapstone has the very useful characteristic of storing/releasing heat, and smoothing temperatures. And it looks great. Definitely not a gimmick.

 

[leeave96]

Very interesting replies.

One of the reasons I asked the question is that one can't simply go out and try/buy multiple stove type, soapstone, steel or cast - so everyone's input is informative.

One thing about my Woodstock Keystone that is very impressive is the construction of it and how it effects the heat cycle. Though it's mostly soapstone, it behaves like both a soapstone and cast iron stove - let me explain.

The soapstone is slow to heat-up - as expected. But while the stove is heating-up, the front of the stove (which is mostly glass and cast iron) is radiating heat from the get-go. As the stones come up to temperature, the whole stove is radiating heat. Once the stove hits a crusing temperature, it almost seems like there is a thermostat at work and that, I believe, is the soapstone. It is dampening the spikes and releasing it's heat into the room as the fire burns down - just like a thermostat. The other night while watching a football game, I was amazed how constant the room temperature stayed over a period of about 3 hours, then as the wood continued to burn down, the room temps started to drop a little at a time until I reloaded the stove for another burn cycle.

So in the end, the soapstone really holds heat and releases it - but nothing like a brick or soapstone hearth, there is simply not enough mass to the stove's stones. But in terms of regulating the temperature spikes, both low and high, the soapstone is working as advertised.

Not owning a steel plate stove or a cast iron stove, it's hard to know how they really compare in terms of even heat over a period of time. If anyone would comment on that aspect, I'd like to know.

One thing I know is that I am really impressed with most all of these newer epa type stoves with their quality and clean burn heat outputs! I could be happy with just about any of them. Maybe if I hit the lottery....

Thanks!
Bill

 

[Bone1099]

I grew up on plate steel freestanding. Seems hard to beat to me if you want intense you got it. If you want soft you got intense at a bit lower level. Now I have a plate steel insert less intense heat from it but I also have trouble keeoing my home warm even with a blower, but I do have the insert in one end of the house and the bedrooms in the other with very poor circulation. Still I cant help but think that if i had a freestanding stove i could more effectively heat my home. For a short period of time i had a VC vigilant the cast iron is beautiful and it seemed to me to be a better conductor. Such as when the stove was hot the top, sides, back, doors even the ash lip seemed the same temp. This surprised me because with my fisher insert the stove top may read 650 on the gauge but the front of the stove (Doors) never seems to radiate very intensely. Both stoves have cast iron doors but the fisher doors are probably 3x as thick. I kinda like the intensity of cast iron but i dont know if it is worth the extra maintenance.

 

[savageactor7]

...So my question is this - from a heating stand point, is soapstone a gimmic? If the point of a stove to impart heat into a space, does the soapstone impede the full heat potential of a stove?...

LOL I always thought so and would never own one. You hear all the Madison Ave hype ..."even heat" talk. Good folks have 'em so I don't press it just like the Amish heater fireplaces on TV. Here in CNY we want a nuclear pile type wood stove ...one that will make your eyes water with discomfort and that's a metal stove only.

As far as the extra soapstone's I suppose once heated you could put it at the foot of your bed to keep the feet warm...folks have been known to do that.

 

[Renovation]

oops, please ignore