Lets compare soapstone, cast, and steel stoves

[Bill]

Lets compare soapstone, cast, and steel stoves.

You have all three stoves installed in three identical rooms, 15' X 15' and 8 feet in height
Each stove has the same chimney, draft
Each stove has 40 pounds of dry white oak
Each fire is started with the same kindling at the same time
The room temperature is 50 degrees, when you start the stoves
Your object is to keep the room comfortable all night

How would you compare these three stoves?

Would you get back the same amount of heat from each stove with the oak?

Which stove could be started in the morning by using the embers?

Which stove would give off the most even heat? And why?

Does a heavy non steel stove loose more heat and efficiency up the chimney before putting out heat?
Or does a heavy non steel stove return lost heat by staying hot longer and improving efficiency after the fire dies down? By efficiency I mean btu's returned to the room from the same amount of wood from the stove. Not burn efficiency.

 

[Rob From Wisconsin]

No Fair
You're stacking the parameters in favor of soapstone!!

But...if you were to ask me from a purely objective standpoint....
I would have to say you get more absolute total heat to your surroundings
with a steel stove. The only problem with steel is that you may get more than
you want in a short period of time.

"Pay me now or pay me later...."

Rob

 

[Bill]

From one cheeshead to another I am not trying to stack the deck. I am just curious how much heat is going up that chimney and how much in the room. I have had several stoves in my lifetime and just recently I got up in the morning and my cheap steel Ashley was warm to the touch and a nice bed of coals on the bottom. So that's fairly long even heat also. I am a curious person and if we have nothing to discuss we don't have an active forum. As Cup's use to say the lively art of conversation.

 

[elkimmeg]

Nice expirment but there are other factors to consider Is a stove a cat stove? Does it have thermatically controlled air?
Are they all tested to the same effeciency The more effecient stove equates to more captured heat.. Are all the fireboxes the same size?
Meaning a large stove will take longer to heat up witha large fire box also more open air space around the wood. It will not produce the same heat withall that extra volume or air around and above the wood load. Are you jugding preformance of h even heat over the longest period of time or when finally they get to the desired point. Soap stone may hold heat longer at the end of the burn cycle but other stoves got to the desired heat level quicker. Are you comparing cat stoves with thermatically controlled secondary air ? to other cat stovess

Are all stoves in the same price range? =Is it fair to compare a Yugo to a BMW? are they all the same weight or does thermal mass not equate?

Actually you are asking comparison to that of lab conditions then I would suggest you look at the GPH for most heat delivered. That is the only published tested data by the EPA.
All other claims are that of manufactures and we all know the fudge factor

 

[Rob From Wisconsin]

From one cheeshead to another I am not trying to stack the deck. I am just curious how much heat is going up that chimney and how much in the room. I have had several stoves in my lifetime and just recently I got up in the morning and my cheap steel Ashley was warm to the touch and a nice bed of coals on the bottom. So that's fairly long even heat also. I am a curious person and if we have nothing to discuss we don't have an active forum. As Cup's use to say the lively art of conversation.

Yep, my inlaws used to have an old Ashley stove. Pre-EPA, air-tight construction.
Put in a lot of wood, choke-off the air, and slowly let it smolder away.
Really gunked-up the chimney fast as a result. But, long burn times.

In my mind, it would stand to reason that the more mass you have between you
and the fire (soapstone, cast iron, etc.), the more it behaves as an insultator.
Perhaps the insulation value difference is minimal....I don't know for sure.

Rob

 

[Bill]

Elk: Great response, I would like to make this fun, lets assume they are three stove the same size fire box, lets say 2 cubic feet, and none have automatic draft controls, or cats, but if you want throw them in also, lets compare.

 

[BrotherBart]

Well, let's see here. 50 degree house so by the time you get a bed of coals built up in the stone stove, load it up and get enough heat coming out of it to start warming those cold walls up and then finally warm the house it will be morning and you will be at work on your first coffee break.

 

[Todd]

They would all be about the same as far as heat output, but the steel and cast would give off their heat quicker and die faster than the soapstone.

 

[Corie]

The lower thermal resistance of the steel and cast iron means more heat will be transferred into the room at a faster rate, assuming EVERY other factor is equal. However, if the stoves are identicial in combustion efficiency, than its not that the soapstone stove is losing any of the energy that isn't transferred to the room, its just that it is being absorbed as energy storage into the stones themselves. Since energy is not destroyed, that energy imparted to the stones would eventually be transferred to the room as well.


However, that diatribe contributes nothing to what you want to know. All factors being equal, the steel stove will probably get the room to temperature first, followed closely behind by the cast iron stove.

Of course, within the cast iron stove you must observe differences. The old VC stoves have a single layer of cast iron between the fire and the room and thus get up to temperature very quickly. Newer stoves have thermal insulation, so the heat transfer to the room is slowed somewhat because the cast iron reaches temperature more slowly. Also, some cast iron stoves, like the Pacific Energy Alderlea(sp?) are a steel firebox surrounded by cast iron asthetic panels. It stands to reason they would bring the room temperature up at about the same speed as the insulation cast iron construction, give or take of course.

 

[Bill]

Just curious how 500 pounds of soapstone can hold more heat than 500 of cast? Is it thermal mass?

 

[stoveguy2esw]

Just curious how 500 pounds of soapstone can hold more heat than 500 of cast? Is it thermal mass?

not thermal mass as being the same weight they would be equal in thermal mass, its simply the two materials absorb and release energy at different rates, kind of like with electricity, some metals conduct electricity ,more easily than others. some materials conduct heat more easily than others (steel). some materials actually store heat better (soapstone) IMHO cast is kinda in between having less easy conduction, but better heat retention than steel, but easier conduction and less retention than soapstone (pound for pound)

 

[jpl1nh]

ok, so if all the stoves are identical in every way except the material they are made out of, then would the 40 lbs of white oak take the same amount of time to burn in each stove?

 

[Rob From Wisconsin]

The lower thermal resistance of the steel and cast iron means more heat will be transferred into the room at a faster rate, assuming EVERY other factor is equal. However, if the stoves are identicial in combustion efficiency, than its not that the soapstone stove is losing any of the energy that isn't transferred to the room, its just that it is being absorbed as energy storage into the stones themselves. Since energy is not destroyed, that energy imparted to the stones would eventually be transferred to the room as well.


However, that diatribe contributes nothing to what you want to know. All factors being equal, the steel stove will probably get the room to temperature first, followed closely behind by the cast iron stove.

Of course, within the cast iron stove you must observe differences. The old VC stoves have a single layer of cast iron between the fire and the room and thus get up to temperature very quickly. Newer stoves have thermal insulation, so the heat transfer to the room is slowed somewhat because the cast iron reaches temperature more slowly. Also, some cast iron stoves, like the Pacific Energy Alderlea(sp?) are a steel firebox surrounded by cast iron asthetic panels. It stands to reason they would bring the room temperature up at about the same speed as the insulation cast iron construction, give or take of course.

Thanks for the scientific explanation.
Although, I often times wonder how much combustion efficiency translates into emitted heat?
What I mean to say is that a lot of insulating materials are put into place to assure that max.
heat is focused in the firebox area & thus increase rated efficiency. But, as a result, how much
of that heat goes shooting up the chimney, because there is less metal surface area for the heat
to be emitted before it is sent up the flue (more firebrick/insulation)?? This was perhaps less of a problem
on older "air-tight" stoves, where "efficiency" meant how much heat you got into a room, and not
how little smoke you sent up the flue.

Rob

 

[tradergordo]

ok, so if all the stoves are identical in every way except the material they are made out of, then would the 40 lbs of white oak take the same amount of time to burn in each stove?

I think ALL of the questions in this thread including the original post would have to be lab tested - but as Elk pointed out - there are almost too many factors to have a reasonable "control" for the experiment. As for this specific question - assuming identical stove designs AND assuming all stoves reach temps which support efficient burning - the cast iron stove should burn the longest, steel almost the same, and soapstone slightly shorter. The reason is that soapstone has poor thermal conductivity, this results in less heat being delivered to the room, and more heat building up inside the firebox - a hotter firebox results in shorter burn times (again, the big assumption here is that even with the cast iron stove the firebox is hot enough to support full secondary combustion).

Personally I think there are a lot of myths that people believe when it comes to stove materials. I've seen one frustrated person comment in these forums about people ascribing "magical properties" to soapstone and I have to agree with this assessment (for example some say it absorbs all the heat like a sponge absorbs water - then gives it all back - this is junk science - yes it absorbs heat and stays warm longer - but there is a net loss).

Its also "common knowledge" (probably wrong) that steel heats up faster than cast iron but doesn't hold its heat as long - I do not believe this is true - the thing is that many (most?) steel stoves are THINNER than cast stoves - which is the ONLY reason they can heat up faster and lose their heat faster when the fire goes out - however there are plenty of steel stoves today that have just as much mass as their cast iron equivalents. When you compare a 450 lb. steel stove with a 450 lb cast iron stove - these properties (heat up time and cool off time) are almost identical. On paper - cast iron should heat up SLIGHTLY faster and cool down SLIGHTLY faster than steel because it has a slightly higher thermal conductivity than steel but in reality I doubt you would even be able to tell the difference.

As for soapstone - it has terrible thermal conductivity - which is why it takes so long to heat up and cool down after it is heated up - this should mean more wasted heat out the chimney EVEN AFTER full thermal mass has been established - this is also probably why Woodstock rates their own soapstone stoves so low as far as recommended heating area and so many reviewers have said it takes too long to heat up (yes, I know, others here don't believe the reviews). The simple fact is that anyone could turn their steel or cast iron stove into a soapstone stove just by putting some soapstone (or other rocks) on top of it!

Note that I don't think soapstone is necessarily a bad choice - I think in certain situations it could work well, but from a purely "heat delivered to your living space" argument its the worst. From an "even heat" argument - again there is a cost to this - less total heat delivered to the room - if even heat is important to you then maybe you should go with soapstone. I personally would rather have my house heat up to say 75 degrees while the fire is going good, and perhaps fall to 65 after the fire dies out, than to have a stove that takes a long time (comparatively) to initially heat up the house and not deliver as much heat to the room while burning only to get a couple degrees of residual heat in the morning after the fire has died down.

 

[webbie]

Actually you are asking comparison to that of lab conditions then I would suggest you look at the GPH for most heat delivered. That is the only published tested data by the EPA.
All other claims are that of manufactures and we all know the fudge factor

We must have a scientist here to correct me if I am wrong, but Grams per Hour is not indicative of total efficiency when comparing wood burning appliances. Does everyone here know how light ONE GRAM is? So whether or not a stove creates another gram of particulates/soot (about 1/500 of a pound) within a hour does not state comparative efficiency.

Here is why: As we have went over before, the efficiency of a stove is calculated as -
Combustion Efficiency TIMES Heat Transfer Efficiency

OK, so let's take one stove that burns the wood at 95% combustion efficiency
and then transfers the heat at 75% efficiency

This stove is 75x95% or somewhere around 73% total efficiency.

Take another stove that burns at 97% efficiency - and transfers heat at 70%
This one burns more efficiently but has less total efficiency - maybe 68%

Let's take an extremely hot burning fireplace with poor heat exchange (like a Refractory-type Rumford fireplace) - this might have a very low Grams per Hour, but only a 30% total efficiency. To confuse matters more, there are so many variables in terms of burn time, etc. that selection becomes even more confusing.

We discussed this before, but in the case of the new VC's with the very hot flue collar - the manual shows that you need to have the pipe really far from the wall, and this is with a flue collar heat shield - well, why do they need the flue collar heat shield? Answer: Because too much heat is going up the flue!

Using EPA data is something which the EPA themselves tells customers not to do - and dealers have cautioned customers against this for over a decade - so I refuse to endorse those tests. If any manufacturer wants some bragging rights, they should do cordwood tests on their own dime and publish the results.

I have written a basic article comparing these materials:
https://www.hearth.com/econtent/index.php/articles/comparing_stove_materials/

But in the end, there are so many individual circumstances that a shopper has to take MANY things into consideration when comparing stoves. For instance, above VC would obviously put out a GREAT deal more heat transfer efficiency when used with 6 feet or more of stove pipe - say straight up or up a few feet and then out the wall. Then there is the matter of heat storage - and a cast or steel stove may act like a soapstone one if it is closely surrounded by a lot of interior masonry.

One of the best features of hearth.com is that the shopper can come here and learn about these differences as related to their exact needs and installation.

For some, the Blaze King cat which holds 100 lbs of wood and can burn 24+ hours easily is a score - for others a fast hot non-cat is the best. Something that we don't discuss often is the style - and VC has (in general) set the pace for stoves which look like fine furniture. There are many who will have nothing less in the living room!

The new stoves with more modern design are also interesting - I'm told that they are mostly fast and hot burners.

 

[BigBarney]

Tradergordo and Craig have pointed out many of the facts about different stove materials. Combining their info tells us that a steel/cast iron stove is the

best for heat transfer and that soapstone with its thermal conductivity about 40 times slower a large amount of the initial burn would be lost up the

chimney.Actually fire brick per # has almost the same heat storage ability.A soapstone stove would radiate longer but at a extremely slow rate due to its

poor thermal conductivity.

Actually a boiler is almost 5 times as efficient at heat storage because water has spec heat of 1,allowing much more storage in a smaller amount of material.


40# of white oak has about 224,000 btu after taking out 20% moisture,in 7-8 hours you only have 32000 to 34000 btu/hr to heat the 1800cuft of air in the room.

Then at the 73% total efficiency 24000btu/hr would be available to heat the room,not even taking into consideration the heat loss over the 7-8 hours.


BigBarney

 

[TruePatriot]

Re:

I think ALL of the questions in this thread including the original post would have to be lab tested - but as Elk pointed out - there are almost too many factors to have a reasonable “control” for the experiment. As for this specific question - assuming identical stove designs AND assuming all stoves reach temps which support efficient burning - the cast iron stove should burn the longest, steel almost the same, and soapstone slightly shorter. The reason is that soapstone has poor thermal conductivity, this results in less heat being delivered to the room, and more heat building up inside the firebox - a hotter firebox results in shorter burn times (again, the big assumption here is that even with the cast iron stove the firebox is hot enough to support full secondary combustion).

Personally I think there are a lot of myths that people believe when it comes to stove materials. I’ve seen one frustrated person comment in these forums about people ascribing “magical properties” to soapstone and I have to agree with this assessment (for example some say it absorbs all the heat like a sponge absorbs water - then gives it all back - this is junk science - yes it absorbs heat and stays warm longer - but there is a net loss).

Its also “common knowledge” (probably wrong) that steel heats up faster than cast iron but doesn’t hold its heat as long - I do not believe this is true - the thing is that many (most?) steel stoves are THINNER than cast stoves - which is the ONLY reason they can heat up faster and lose their heat faster when the fire goes out - however there are plenty of steel stoves today that have just as much mass as their cast iron equivalents. When you compare a 450 lb. steel stove with a 450 lb cast iron stove - these properties (heat up time and cool off time) are almost identical. On paper - cast iron should heat up SLIGHTLY faster and cool down SLIGHTLY faster than steel because it has a slightly higher thermal conductivity than steel but in reality I doubt you would even be able to tell the difference.

As for soapstone - it has terrible thermal conductivity - which is why it takes so long to heat up and cool down after it is heated up - this should mean more wasted heat out the chimney EVEN AFTER full thermal mass has been established - this is also probably why Woodstock rates their own soapstone stoves so low as far as recommended heating area and so many reviewers have said it takes too long to heat up (yes, I know, others here don’t believe the reviews). The simple fact is that anyone could turn their steel or cast iron stove into a soapstone stove just by putting some soapstone (or other rocks) on top of it!

Note that I don’t think soapstone is necessarily a bad choice - I think in certain situations it could work well, but from a purely “heat delivered to your living space” argument its the worst. From an “even heat” argument - again there is a cost to this - less total heat delivered to the room - if even heat is important to you then maybe you should go with soapstone. I personally would rather have my house heat up to say 75 degrees while the fire is going good, and perhaps fall to 65 after the fire dies out, than to have a stove that takes a long time (comparatively) to initially heat up the house and not deliver as much heat to the room while burning only to get a couple degrees of residual heat in the morning after the fire has died down.

What a great discussion! I especially appreciate tradergordo's comments above, and those of Craig and Big Barney.

I've bolded the comments, above, that really resonnated with me, from tradergordo.

I have felt that the "hype" of soapstone is too often just swallowed whole, with little or no "critical thinking (i.e., questioning what you think you know).

I have often wondered what the advantage of soapstone is, in a stove that runs 24/7?

I have also wondered why I should want the heat to be released later, into the house envelope, (soapstone) than earlier (plate steel), partiuclarly if, again, the stove runs 24/7? I too suspect that this must result in more heat escaping up the pipe than into the room, compared to a stove not "insulated" with soapstone. One doesn't leave their cold-soaked winter coat on, when they come inside to get warm by the stove, right?

I've asked owners of soapstone stoves to explain this to me, and I get a mishmash of "It's radiant heat, see? And ah, it's...well, it's kinda like--you know, it warms you, not the room, see?"

"Yeah, but I want my room warm too, don't I?"

They get off into the weeds comparing radiant heat to convective heat, and never answer my question about why it's better to get the heat later rather than sooner.

It reminds me of the early 1980's, when the domestics went almost completely to FWD cars. Yes, it has certain advantages, mostly in low-speed, low traction situations (snowy parking lots) and definite drawbacks in high speed handling. Doubt it? Don't--when you put the engine and trans and diff all in the same end of the car, you are very far away from the ideal 50/50 front/rear weight distribution of a dedicated racing machine. Only the wizards at Porsche got (partly) around that problem, and only recently--Porsches used to crash backwards 40% of the time, due to their rear weight bias.

Now, finally, we're seeing a return to rear drive, in the larger, domestic cars. And guess who never gave up on RWD? Ferrari, Lambo, 'Vette, Jag, Alfa, Lotus, Aston Martin, Porsche, M-Benz, Lexus, Infiniti etc...in short, the higher-performance cars. Why? Hi-speed vehicle dynamics--a 50/50 weight distribution keeps the physics gods happier.

Hey--get whatcha like--I'm just tired of hearing about the mystique of soapstone, and wondering why I'm too stupid to understand it's supposed "superiority...."

Peter

 

[tradergordo]

I have felt that the "hype" of soapstone is too often just swallowed whole, with little or no "critical thinking (i.e., questioning what you think you know).... I’m just tired of hearing about the mystique of soapstone, and wondering why I’m too stupid to understand it’s supposed “superiority....”

The first thing I noticed when I visited the Tulikivi website (bottom part, after the animation loads): "stone is an ancient material that throbs with primordial energies" hmmm, YEAH. Then I clicked their "fireplaces" link, and I see: "Soapstone... Quite extraordinary. It’s no wonder then, that this mysterious stone is also a pleasure to work with."

Does soapstone also contain some mysterious pleasure giving primordial energy? Can we test that in the lab too?

 

[Harley]

Hey--get whatcha like--I’m just tired of hearing about the mystique of soapstone, and wondering why I’m too stupid to understand it’s supposed “superiority....”


The "get whatcha like" is what makes the most sense of all. In reality, there's probably not any one material that is "superior" to the others in all cases. Each house/setup/location/weather is a little different. Everyone easily should find the right stove for their particular application, with research, and a good dealer.

Growing up, we had a steel plate stove (All-Nighter). When I bought my house, I put in a cast iron stove (VC). I recently changed some things around, and now have a soapstone stove (Hearthstone). They all did very well and served their purpose and heated the area they needed to heat.

The soapstone stove works for me pretty well in my particular situation. I don't think there's anything superior, or "mystical" about it, but in my case, I happen to work longer hours during the colder times of the year. I would consider myself a 24/7 burner, but with almost any stove with my setup, the fire is out by the time I get home. With the soapstone, to me, it seems that since the stone is still very warm, its a quick stir of the coals or what is there - throw in a few splits, and it off and running without having to re-start the fire with kindling. Maybe it was "wasting heat" up the chimney, but the increased draft from everything being warm seems to work well for the re-starting.

No magic, no mystery - just seems to work out pretty well for me, and I like it.

 

[Gunner]

Actually you are asking comparison to that of lab conditions then I would suggest you look at the GPH for most heat delivered. That is the only published tested data by the EPA.

Here we go again.....

How many times does this need to be explained Elk!

He is your homework:
-How many btu's are in a gram of wood?
-multiply that number by 24 to get total "extra" btu's for a 24hr period.
-Write that number down on a piece of paper....next time you use the washroom, wipe your arse with the paper :lol:

 

[Todd]

ok, so if all the stoves are identical in every way except the material they are made out of, then would the 40 lbs of white oak take the same amount of time to burn in each stove?

As for soapstone - it has terrible thermal conductivity - which is why it takes so long to heat up and cool down after it is heated up - this should mean more wasted heat out the chimney EVEN AFTER full thermal mass has been established - this is also probably why Woodstock rates their own soapstone stoves so low as far as recommended heating area and so many reviewers have said it takes too long to heat up (yes, I know, others here don't believe the reviews). The simple fact is that anyone could turn their steel or cast iron stove into a soapstone stove just by putting some soapstone (or other rocks) on top of it!

Note that I don't think soapstone is necessarily a bad choice - I think in certain situations it could work well, but from a purely "heat delivered to your living space" argument its the worst. From an "even heat" argument - again there is a cost to this - less total heat delivered to the room - if even heat is important to you then maybe you should go with soapstone. I personally would rather have my house heat up to say 75 degrees while the fire is going good, and perhaps fall to 65 after the fire dies out, than to have a stove that takes a long time (comparatively) to initially heat up the house and not deliver as much heat to the room while burning only to get a couple degrees of residual heat in the morning after the fire has died down.

Well, I'm no scientist or expert on thermal conductivity, but I can honestly say my stack temps are lower with this stove than any other stove i've burned before, so there is no more heat going up my chimney than a steel/cast stove would put up there. Also the firewood consumption is down. Maybe it's the cat that helps? As far as heat up time, I can get mine up to 500 in less than 1 hr, is that too long? I really don't understand why someone would want such a big swing in temps? I like a constant even temp. Your right that the soapstone manufactures try to state their product as magical, and I'm sick of it to, but every other manufacture has some kind of sales pitch to sell their product. There is a stove out there for everyone. I guess one has to burn all types to really see what he likes best, and I vote soapstone.

 

[jpl1nh]

It's my impression there are things people will just never agree on. They include religion, politics, choice, cat vs non-cat, soapstone vs cast iron vs steel, and who the most beautiful woman is. Sure is fun talking about it though.

 

[stoveguy2esw]

ok, so if all the stoves are identical in every way except the material they are made out of, then would the 40 lbs of white oak take the same amount of time to burn in each stove?

yes if the units were constructed identically they would perform that way , as far as burn times, the question is heat transferrance, in which case you would have to look at the materials, soapstone would not survive at 1/4 inch thickness its stock in trade is thick heat absorbing material, steel does not have to be that thick and cast does not either, if a stove with 1/4 inch soapstone walls were built it would react like a steel stove , throw a lot of heat quickly , but it would not be able to handle it and would fail.steel at 3/4 inch thickness would end up holding heat like soapstone but would be a slow mover as far as "heat now" is concerned , as would cast. soapstone is thicker because its inherant strength demands it, steel heats up quicker because its thinner and cannot hold as much heat because of that so it must radiate faster. this plays into the hand of cast as the cast units can select how thick they make them to gain either speed or longevity. the real key is this how completely can you burn each split, and how much of that heat can you transfer to the room you are heating, because if you cannot transfer, or worse, if you cannot completely incinerate, then what is left over leaves either up the flue , or out with the ash. burning wood is a simple task, burning it completely takes thought. essentially heat is required, air movement (turbulence) is required, and fuel is required. now here is the trick, concentrate the heat , the turbulence and the fuel inside an environment that does not allow rapid escape of air, its a balancing act because you must pull air out to create turbulence by drawing air in. theoretically wood can be burned at 90%+ efficiency provided that there is enough temperature and turbulence available to do so. practically , it aint happening the secondary part of the burn would have to become a third stage and fourth etc... but a well designed modern woodstove, regardless of material its made from, is able to incinerate wood to levels that were not achievable 25 years ago. as for the GPH emmissions, think about it this way. when units are tested for emmissions (regardless of firebox size) they load a charge of 15 pounds of douglas fir dried to 13 % for the test ( thats why you might see a btu output on an epa door tag that is higher in a small stove and lower in a big stove which is rated at a higher square footage of heating capacity)this in mind , the more completely you incinerate the wood the more energy you release from the wood, and the less unburned wood (particulate matter IS unburned wood)leaves through the flue. so in that mindset, GPH does matter, 1.6 GPH leaving through the flue during testing was generated by about 1500 popsickle sticks worth of wood, actual loads would be obviously larger, therefore the actual PM release is higher by a factor of up to 3 with wood at the same moisture content, higher still as the moisture level goes up and the char stage lasts longer.BUT!! 3 times the wood load means 3 times the heat output (pending moisture content) now, if a stove released say 3.2 GPH in testing (just to make the math easier) that means that in the real world taking the factor of 3 in consideration the loss of fuel up the flue is increased by a power of 3 or higher (moisture) and that friends is why GPH does factor in. unless you are a member over in the anti- hearth forum and are fooled into thinking that you will only get the optimum efficiency for a few months.

 

[Gooserider]

Seems to me like none of the EPA stoves are that different in efficiency - they all seem to loose about the same amount of heat up the chimney, which means they all are going to deliver the same total volume of heat to the room - sooner or later...

To me the question of the different materials is how they regulate the heat delivery. We all know about the fire cycle, and how over the course of burning a load of wood, the fire will put out different amounts of heat at different times. The question is how closely does the amount of heat the stove releases to the room track the amount of heat the fire was putting out shortly before?

In theory a thin steel plate stove would track the fire closely, getting very hot when the fire did, and cooling down when the fire cooled. This might make some people unhappy because they would be baked out of the room at some points and not quite warm enough at others.

OTOH a soapstone stove, because of its thickness and poor thermal conductivity will tend to even out the heat flow - it won't get as hot during the fire peak temps, and because it is finally transferring those peak temp BTU's when the fire cools, it won't get as cold either.

A cast stove would fall somewhere in the middle.

If one were to draw a graph of stove exterior temp (or BTU's of heat transfered to the room) over time, I would expect the thin steel stove to have a curve with lots of peaks and valleys matching load times and the fire cycle. The soapstone stove would probably show a much flatter curve, and again the cast stove would be somewhere in between...

So much for theory.... In practice, the extra insulation added to the insides of most EPA stoves in order to get and keep the fireboxes hot enough for 2ndary combustion will cause all the materials to have a curve that looks more like soapstone. Couple this with most manufacturers expecting that customers would prefer a stove with a flatter heat delivery curve (possibly with lip service paid to rapidly getting the stove up to temp), I suspect that there won't be HUGE differences between the materials - just enough to fuel debates like this one!

Gooserider

 

[tradergordo]

ok, so if all the stoves are identical in every way except the material they are made out of, then would the 40 lbs of white oak take the same amount of time to burn in each stove?

yes

This is ONLY true if firebox temps are the same in all stoves. That's a big assumption. The stove material should (in theory anyway) affect firebox temps (how much is a total guess, which is why a lab test would be great). Firebox temps impact burn times (temps high enough for optimal secondary combustion=GOOD, temps above and beyond what is required for secondary combusion=bad). But perhaps the debate is meaningless IF all the manufacturers insulate the firebox (for example using varying amounts of firebrick) to achive approximately the same firebox temps no matter what the outer material consists of (steel/iron/stone).