theoretical question

[Corey]

Savage - you'd just have to compare the specific heat capacity and thermal conductivity of the stone and the specific heat capacity of the water and thermal conductivity of the container it's in. I'm sure conditions could be created where either one could hold more heat and release it faster or slower. ie - the water in my water heater would hold heat for days due to the insulation. That same amount of water in an aluminum barrel with heat sink fins on the sides would cool off pretty fast.

The key is how much heat do you want to store, and how fast do you want to store/release it.

 

[karri0n]

Proof of concept.... Complete with ridiculous price markup!



http://www.vermontwoodstove.com/wssstops.htm

 

[bokehman]

Proof of concept...

Those are just a decoration, not a thermal reserve. A 40 lb piece of soapstone raised 400 degrees is barely storing 3000 BTU.

 

[jebatty]

By way of approximation, most stone has a specific heat capacity of about 0.2 or a little more, meaning 1 lb of stone stores 0.2 btu per degree. Water has a specific heat capacity of 1.0, or 5 times as great.

Weights of stone/volume are somewhat variable, but 145 lbs/cu ft is a pretty good average. Water weight is 62 lbs/cu ft. Stone by volume stores a little under 1/2 the heat an equal volume of water would store, and stone weighs about 2 1/3 times what an equal volume of water would weigh.

If you want to store heat, use water.

Modern technology has already invented what might be called a water vessel to capture, store, and then release heat from a wood burning appliance. It's call a wood fired boiler. ;-) Look at the Boiler Room to know everything there is to know on this topic.

On the other hand, stone doesn't boil and blow its top, so while water can be raised only to 212F before that happens, stone can be raised to 1000F and more (melting point? I don't know, but probably well in excess of 2000F). Thermal mass, if you have a way to use it, can be very effective to store and release heat.

 

[Stevebass4]

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.

looking forward to your results!! please keep us posted

 

[Martin Strand III]

This recent blog is actually an old (and good) idea popular in central Europe some time ago.

1000 years ago: the Steinofen
300,000 years before that: Homo erectus heated rocks (apparently)

See the details of the author's personal experience with "IRON/MASONRY COMBINATION SYSTEMS" including

* the critical dimension between the masonry and the metal stove for heat conduction
* the requirements for a HOT fire chamber (more masonry than in most metal stoves)
* inclusion of convection vents in the masonry surround
* use of a heat exchanger instead of a masonry smoke channel system
* what to actually expect from such a beast (efficiency, etc)
* a diagram of a common design used in Austria and Germany

A modern twist on this could become wildly popular for heating needs North America.

Aye,
Marty

Ref:
The Book of Masonry Stoves: Rediscovering an Old Way of Warming,
David Lyle, Chelsea Green Publishing Co ((broken link removed)),
pp. 130 - 133, 1984.

 

[karri0n]

This recent blog is actually an old (and good) idea popular in central Europe some time ago.

1000 years ago: the Steinofen
300,000 years before that: Homo erectus heated rocks (apparently)

See the details of the author's personal experience with "IRON/MASONRY COMBINATION SYSTEMS" including

* the critical dimension between the masonry and the metal stove for heat conduction
* the requirements for a HOT fire chamber (more masonry than in most metal stoves)
* inclusion of convection vents in the masonry surround
* use of a heat exchanger instead of a masonry smoke channel system
* what to actually expect from such a beast (efficiency, etc)
* a diagram of a common design used in Austria and Germany

A modern twist on this could become wildly popular for heating needs North America.

Aye,
Marty

Ref:
The Book of Masonry Stoves: Rediscovering an Old Way of Warming,
David Lyle, Chelsea Green Publishing Co ((broken link removed)),
pp. 130 - 133, 1984.

Make that http://www.chelseagreen.com

 

[awoodman]

I built in thermal mass arround the stove when I put the addition on to the house.

(broken image removed)

The pic. shows xmas. stocking hanging from a mantel on the other side of the wall.

 

[karri0n]

Does that alcove keep the heat well?

 

[madrone]

How about kiln shelves? They'd look a little better, and could be cut to fit. A nice thick one might be just the right balance of mass. Might look nifty with some glaze crazed all over it...

 

[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.

looking forward to your results!! please keep us posted

Will do . . . I'm just waiting for my soapstone to be delivered.

 

[meathead]

Hard to go wrong for $30

 

[Martin Strand III]

Well, I'm taking the plunge... 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.

Firefighter:

I suggest putting the slab on legs FIRST. If your slab is directly on the stove, you may crack it. But then, it's your 30 bucks... On second thought, since they are not fixed together (with refractory mortar), it may be OK.

Also, a slab of soapstone your size on top of a metal stove does not really qualify as a "thermal mass" heater. Therefore, have realistic expectations about significant improvement in heating over what you have to start with.

Aye,
Marty

 

[firefighterjake]

Hard to go wrong for $30

That's what I figured . . . if this whole thing doesn't work out very well or look good I'll have a nice piece of soapstone to carve.

 

[firefighterjake]

Well, I'm taking the plunge... 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.

Firefighter:

I suggest putting the slab on legs FIRST. If your slab is directly on the stove, you may crack it. But then, it's your 30 bucks... On second thought, since they are not fixed together (with refractory mortar), it may be OK.

Also, a slab of soapstone your size on top of a metal stove does not really qualify as a "thermal mass" heater. Therefore, have realistic expectations about significant improvement in heating over what you have to start with.

Aye,
Marty

True, true . . . I'm not expecting to add a small slab of soapstone and instantly have my cast iron stove perform the same as a soapstone for a fraction of the cost . . . just thinking it may look good and provide a little more mass to heat up and radiate out when the fire dies (akin to my slate hearth which provides some, but not a lot of residual heat after the fire dies down.)

 

[madrone]

I suggest putting the slab on legs FIRST. If your slab is directly on the stove, you may crack it. But then, it's your 30 bucks...

Not likely. Even if you shocked it it's not likely to crack from thermal expansion. Soapstone doesn't behave that way. I've seen it attacked with a welding torch, and it just eventually crumbles, but we're talking 3000*. The stove, even running REALLY hot isn't going up that fast anyway. It's pretty amazing how long the stuff holds heat. It's fragile on it's own, though, so do handle it carefully before it's in place.

 

[madrone]

Proof of concept.... Complete with ridiculous price markup!



http://www.vermontwoodstove.com/wssstops.htm

OMFG! That's one of the worst rip-offs I've ever seen.