theoretical question

[potter]

So, I'm not going to do this because of how it would look, but.... I have piles of refractory hardbrick sitting around (as does AP no doubt). Why couldn't a person add a layer or more of hard brick to the top of a stove. It would slow down heat output at the beginning, but much like a soapstone stove the bricks would load up heat and radiate longer. Several members have talked about soapstone tops for their Oslos, Bricks could be cut to fit and made to look better. Well, I have more couch/computer time because of an injury, so got me thinking. The only other stoves I think "Well, maybe I shoulda.." are the soapstone cats. Very content with my Oslo, though.

 

[firefighterjake]

What does this hardbrick look like . . . not being a potter I picture it looking like firebrick and while you may get some benefits I can't say that I could sell my wife on putting a bunch of firebrick on top of the stove . . . but she would go for a nice looking soapstone slab.

 

[potter]

What does this hardbrick look like . . . not being a potter I picture it looking like firebrick and while you may get some benefits I can't say that I could sell my wife on putting a bunch of firebrick on top of the stove . . . but she would go for a nice looking soapstone slab.

Yes, it's just firebrick. Sorry for the lingo. In pottery we have 'soft' bricks too, insulating bricks that weigh much less and are made to 'reflect' heat. This, as opposed to 'hardbrick' which absorbs and loads up heat and then later reflects heat.
And, yes, the looks problem is why I said "theoretical".
But there are some using stoves in basements, less concerned about aesthetics. Also, I think I remember you discussing soapstone- wonder if you could have a piece custom cut that was thick and could sit on existing top rather than waiting for Jotul to make something available.

 

[Jags]

I have wondered about this as well, including the discussion of soapstone added to the top of a stove. The only question I would like answered (because I don't know) is: Will adding a layer of whatever ON TOP of a stove slow down the intended heat dissipation to a point where internal or stove top temps could rise to an unintended level?

That is really the only concern I can come up with. I am guessing that this is part of the reason that soapstone stoves have a lower recommended stove top temp then a cast or steel stove.

Edit: I really wish we had some young stove engineer types that frequent the board that might be willing to shed some light on this ;-P

 

[firefighterjake]

What does this hardbrick look like . . . not being a potter I picture it looking like firebrick and while you may get some benefits I can't say that I could sell my wife on putting a bunch of firebrick on top of the stove . . . but she would go for a nice looking soapstone slab.

Yes, it's just firebrick. Sorry for the lingo. In pottery we have 'soft' bricks too, insulating bricks that weigh much less and are made to 'reflect' heat. This, as opposed to 'hardbrick' which absorbs and loads up heat and then later reflects heat.
And, yes, the looks problem is why I said "theoretical".
But there are some using stoves in basements, less concerned about aesthetics. Also, I think I remember you discussing soapstone- wonder if you could have a piece custom cut that was thick and could sit on existing top rather than waiting for Jotul to make something available.

I'm still toying around with the idea . . . I've located a place up in Fort Fairfield, ME . . . I just have to find the time and (more importantly) the inclination to send them some measurements. I figure if it works on the stove top it will be a nice addition . . . and if it doesn't work as well as I am hoping I can still put it to good use. My main issue at this point to tell the truth is what to do about the stove top thermometer -- not sure if I should cut a full piece to fit on the entire top, get a custom piece with a corner cut out for the thermometer or just get a smaller piece on top.

 

[firefighterjake]

I have wondered about this as well, including the discussion of soapstone added to the top of a stove. The only question I would like answered (because I don't know) is: Will adding a layer of whatever ON TOP of a stove slow down the intended heat dissipation to a point where internal or stove top temps could rise to an unintended level?

That is really the only concern I can come up with. I am guessing that this is part of the reason that soapstone stoves have a lower recommended stove top temp then a cast or steel stove.

Edit: I really wish we had some young stove engineer types that frequent the board that might be willing to shed some light on this ;-P

Yes . . . it sure would be nice if some stove engineer could offer some advice . . . but what's the chances of some stove engineer frequenting this board?

I do know that in the case of the Oslo Jotul did apparently sell a soapstone top at one time (per a previous attachment in an older thread) . . . I also have noticed that it seems as though most of the heat from the Oslo is radiated out from the front vs. other locations . . . but as you said I would love to know if there are any possible drawbacks or concerns in putting the stone on top. At this point I am heavily leaning towards going ahead and experimenting by getting a piece of stone and monitoring the results.

 

[edthedawg]

I'm not a young stove engineer, but airplanes are in the ballpark, so i'll pipe up with this: if the stone slab you put on top is physically tight to the top of the cast/steel stovetop, with no gap, you're probably going to get good conduction of the heat away from the metal surface into the stone. i'd venture to guess that it might be better than the convection cooling you'd rely on for the uncovered metal. Doesn't seem like it would have much of an insulating factor, which it sounds like you're concerned about...

but...

then i think about the stone once it heats up... would it continue to "absorb" and "radiate" the heat effectively... i think it would, but i'm still trying to come up with a logical real-world-based example.

Our soapstone stoves are just stone - not stone cladding over cast/steel metal surfaces. but i can't intuitively determine whether that's just because it's cheap and works? or if it's actually a performance inhibitor to build any other way?

And then my mental rambling is gonna settle here: If it was a good idea, there'd probably be a few stove manufacturers out there who make a line of stoves like this.

I'll gladly uncap a beverage for anyone who calls some stove mfg'rs and manages to get someone from their engineering dept on the line

 

[bbeals]

I tend to think of this like Jags does. Stoves are air cooled, as boilers are water cooled. Wouldn't want to run my boiler without water and I'm not certain as to the effects of insulating the top of the stove with soapstone. Probably wouldn't cause the stove to melt, but might have the potential for warping the top, given that it would not be able to let go off the heat in the manner it was designed. I too would like to hear from a stove engineer on this one.

 

[Adios Pantalones]

I've thought about this a fair bit- but since I have an insert and the top is separated from the body (air channel)- the top never gets that hot. I would have to direct the air through a brick channel- and now it's getting weird and big.

Castable refractory is really easy to use- that might be the way to go for making a heat sink of some sort. I friggin love castable refractory- it really is amazing stuff.

Oh and- ya- I have lots of brick laying around- mostly soaps. After the last firing and experiment with soda... well, I have some that are fused into bigger bricks now

 

[karri0n]

I've had this idea as well. I think the matter is that the stove is already built or cast thick enough to hold and radiate heat, rather than conduct heat into another solid surface. I would imagine soapstone stoves' metal is thinner and less thermal mass than your average plate steel or cast iron full stove.

As to your quandary FFJ, have it drilled and drop the thermo in! That would look NICE.

Also, I believe thermal mass is the issue here. A large slab of soapstone on top will probably weigh 50-100 pounds. The total weight of the stone on soapstone stoves is a bit higher than that, I believe.


I've also toyed with a similar, if opposite, idea. It seems to me that depending on your profession, and what you have lying around, you start to think "what if I put that on my stove?". I think Man has been doing this for ages. "I wonder what happens if I light THAT on fire..." Anyway, Since I work in IT, and always have computer parts laying around, I was thinking of taking a bunch of aluminum heat sinks that I have, attaching them together, and setting up a fan system that blows across them, to draw the heat off the stove and disperse it more quickly. My concern with this is the same as the one expressed as Jags, only inversed as well. I worry that it could lower my internal stove temp and hinder my secondary combustion.

 

[meathead]

I'd feel safer building a masonry mass around the stove - could be as simple as removing any rear heat shield and setting a slab of soapstone behind the stove or building a sort of half wall soapstone alcove around the hearth. The mass, not being directly in contact with the stove, would obviously take longer to absorb the heat - but it also wouldn't insulate the stove in any significant additional way, and you wouldn't be adding pounds that your stove legs had to bear (to get significant heat retention - you would need to sit a significant slab on top of your stove). No doubt about it, masonry mass is clutch - but personally I'd be hesitant to rest it directly on top of my stove. Besides, you can build a really attractive stove backdrop and surround and get great aesthetic value AND a large warm masonry mass at the same time.

 

[savageactor7]

HUH... I alway thought the firebrick was to insulate the steel so it wouldn't melt like those white blocks on the space shuttle.

 

[Jags]

HUH... I alway thought the firebrick was to insulate the steel so it wouldn't melt like those white blocks on the space shuttle.

Clarified above savage:

Yes, it’s just firebrick. Sorry for the lingo. In pottery we have ‘soft’ bricks too, insulating bricks that weigh much less and are made to ‘reflect’ heat. This, as opposed to ‘hardbrick’ which absorbs and loads up heat and then later reflects heat.

 

[Corey]

Well, I'm not a stove engineer - but I did stay at a holiday inn last night

I would think there are going to be two key factors to consider. One is the thermal conductivity of the material, the other is the specific heat capacity of the material. Thermal conductivity shows how much heat the material would retain around the stove. This addresses concerns of 'overheating due to insulation' mentioned above. Would you wrap your stove in a foot thick blanket of mineral wool insulation? Most people would say "No way, it would overheat and I wouldn't get any heat out through that blanket of insulation" - this insulation has very low thermal conductivity. Likewise, you probably wouldn't think twice about laying a piece of sheet metal on the stove...high thermal conductivity. The other side is specific heat capacity...how much heat can the material hold...think of this as the size of the "thermal battery"

With this explanation, the ballpark numbers I see:

THERMAL CONDUCTIVITY (Btu-in/hr-ft-F)

Soapstone - 42 - 48
Firebrick, Clay (ASTMC62) 6.6

The soapstone is passing about 6.8 times more heat than the firebrick. ie the firebrick is a moderately good insulator compared to the soapstone.

Specific heat capacity (Btu / lb-F)

Soapstone - 0.234
Firebrick - 0.20

So the soapstone and firebrick both have similar ability to hold the heat.

In summary, I think an outer layer of firebrick should be similar to the soapstone in heat capacity, but the thermal conductivity of the brick is much lower which makes it a better insulator. Possibly too good as some have pointed out above.

For grins, you can figure out the heat storage of a soapstone stove...weight of stone x 2.34 x Delta T = Btu's. Say your stove has 200 pounds of soapstone and you fire it to an average of 300F (it will be hotter on the top and cooler on the bottom), then allow it to cool to 70F (230F dT) so 200 lbs x .234 x 230 = about 11,000 btu.

 

[Valhalla]

So, I'm not going to do this because of how it would look, but.... I have piles of refractory hardbrick sitting around (as does AP no doubt). Why couldn't a person add a layer or more of hard brick to the top of a stove. It would slow down heat output at the beginning, but much like a soapstone stove the bricks would load up heat and radiate longer. Several members have talked about soapstone tops for their Oslos, Bricks could be cut to fit and made to look better. Well, I have more couch/computer time because of an injury, so got me thinking. The only other stoves I think "Well, maybe I shoulda.." are the soapstone cats. Very content with my Oslo, though.

Potter,

It may slow down the actual warm-up of your beautiful stove. So, nothing is actually gained. I would suggest that any stove should be allowed to operate as it was designed by the manufacturer.

Enjoy your stove and keep warm!

 

[gerry100]

Assuming a tight gap between the bircks and the stove top two things would happen-

- an effective increase in the thermal mass of the stove resulting in slower warm up and cool down therefore smoothinh hot the tmepratuire transitions.

- by slowing the heat ransfer out of the stove top , the temps in the stove top and top of the firebox will have higher maximums, my guess is that the temps would be well within the design limits but it's still good to be aware.

As siad above, no heat is gained so unless the "distribution " effrects are noticeable it's a wasted effort.

 

[bokehman]

about 11,000 btu.

Which isn't even 2 lbs of wood, or about 1 lb of wood more than it would take to warm up an iron stove of the same weight.

 

[hankjrfan]

I have a friend who mortored or quickcreted stones all over the exterior of an old wood stove. He banks it up, then pours water over the top and uses it for a sauna. He's had no problems with it.

 

[potter]

I'd feel safer building a masonry mass around the stove - could be as simple as removing any rear heat shield and setting a slab of soapstone behind the stove or building a sort of half wall soapstone alcove around the hearth. The mass, not being directly in contact with the stove, would obviously take longer to absorb the heat - but it also wouldn't insulate the stove in any significant additional way, and you wouldn't be adding pounds that your stove legs had to bear (to get significant heat retention - you would need to sit a significant slab on top of your stove). No doubt about it, masonry mass is clutch - but personally I'd be hesitant to rest it directly on top of my stove. Besides, you can build a really attractive stove backdrop and surround and get great aesthetic value AND a large warm masonry mass at the same time.

My current situation is pretty close to this. The stove sits on a cement basement floor and in front of the 5 ft. base of a stone chimney that goes up through the center of the house. No heat shields. If I keep the stove going 24/7 the floor and chimney get incredibly warm. Yesterday morning after burning for several days straight, we had a warm day and I let it go out at noon with house temps at 72*.
Into the evening and overnight temps dropped to 20* outside. Decided not to build a fire and see what happened. Woke up this morning and the house was 62*, and chimney still felt a little warm. Needed to build a fire, but still not bad considering the house isn't that tight.

 

[firefighterjake]

Well, I'm taking the plunge. Just got done e-mailing a guy (Gary) in Fort Fairfield who will be dropping off a 11 x 22 slab of soapstone for me sometime next week for $30. After reading some of the opinions here I decided to think ahead a bit and have also requested a few 2 x 2 pieces for use as "legs" which I'm thinking would provide an air gap in case laying the soapstone directly on the stove has any adverse effects.

My thinking is that I will try laying the soapstone on the top and seeing how things go . . . and then I will try laying the soapstone on top with the "legs" underneath with the assumption that the heat would still get "sucked" up by the soapstone despite an air gap.

If things don't go as planned I will simply use the soapstone slab in front of the stove as "part" of the hearth where it can suck up and radiate out heat . . . and if that doesn't work I'll use it as a cutting board or carve something out of it . . . maybe a ferret.

 

[Adios Pantalones]

Looking at www.sidestoke.com (one of my all time favorite kiln sites), they build a bunch of kilns out of 2 layer hard brick. While it will transmit some heat- they get to woodfire temps with these things. My kiln is high heat hardbrick interior with G2300 brick exterior, with the high heats as through-wall tie courses. The through-wall bricks get hot and stay hot- but you don't feel it until the kiln starts getting way up there. I mean- you can lay your hand on one when the interior temp is above woodstove temps. They may just be too insulating for this, as others have said.

Now- in an air path from a blower- then they would pick up some heat and re-radiate anyway. Were getting into masonry stove territory here.

BTW- IIRC, most ceramic will hold about twice the heat or more of iron, but water blows them all away.

 

[Corey]

That's true...water is of course 1.00 btu/lb-F, but the bad thing there is things get a little tentative around 212F where iron/stone/brick, etc don't have any trouble until much hotter. If you're really looking for heat capacity, pound for pound, hydrogen gas is tops...around 2.5 btu/lb-F IIRC. Of course, density is the killer there!

 

[Adios Pantalones]

LOL- you could use hydrogen liquid, but you'd need a serious pressure vessel

 

[savageactor7]

Wouldn't some kind of water containers retain/radiate heat longer than stone...just asking.

 

[daleeper]

Wouldn't some kind of water containers retain/radiate heat longer than stone...just asking.

My bil used to keep 55 gallon drums of water around his wood stove in the shop, it would help stabilize the temperature of the room quite well. Didn't look like something that you would want in a living space though.