What's the Real Deal on Insulation?

[webby3650]

Now, soapstone cladding or lining is a good idea, not as a structural part of the stove though. No.. It's way too vulnerable.

 

[webby3650]

The progress cranks out heat very fast inferno like demon fire

That's what I'm talking about! Heck ya! Can't wait to try one. A straight soapstone stove can only release a certain amount of heat at any given moment, that's the nature of the stone.
You can't force anymore heat out of it, regardless. Excess heat will go straight up the flue. They are very limited in there heat production, if forced beyond that then there will be issues with excessive heat loss up the flue, or damage to the stones. Woodstock must be excluded in this though, they use two layers of stone, rather than 1 thick stone that hearthstone uses. I really think that there's a good reason for this. I don't think I've ever heard of a cracked Woodstock, while cracked Hearthstones are all too common.

 

[begreen]

That's why I prefer a cast iron clad steel stove. Best of both worlds and not fragile.

 

[jetsam]

I can't speak to stove performance, but cast iron has better thermal conductivity than carbon steel, and both are much more conductive than soapstone.

A little googling says cast iron is around 55 w/mK, carbon steel 35-54, and soapstone is 6-12. Firebrick is in the neighborhood of 1. (Interestingly, I got the low number on soapstone from Tulikivi's website.)

 

[quotejso]

The soapstoneholds heat longer. Plus it looks good.

 

[begreen]

I used to think that too, but have found the cast iron cladding on the Alderlea to work nearly as well. Looks good too.

 

[electrathon]

The soapstoneholds heat longer. Plus it looks good.

The reason the stove stays hot is because it does not want to release the contained heat. It both acts like an insulation layer keeping the heat inside the stove and when it does finally get hot it holds the heat so that the heat energy is contained in the stones and not released into the room. This is one of the reasons that cooking on top of a soapstone stove is more difficult that on a cast stove.

It is sort of funny that this thread just came up. My son is in engineering school currently and they were discussing this same basic concept about a week ago. He called me afterwards and commented it was likely a heating mistake that I bought the soapstone stove (I had already figured that out from experience). For the record, I am not saying it is not possible to heat using a soapstone stove, just that for the same amount of wood consumed (heat created or BTUs) your house would be warmer with a cast stove over a soapstone stove.

Also, the soapstone is pretty, I get a lot of positive comments on the look of the stove. Form over function. My stove sits inside the fireplace opening of a 1930s house, it looks like it belongs there.

 

[jetsam]

The core concept here is that cast iron transfers heat 4-9x faster than soapstone. Soapstone stores more heat per pound- but the amount of heat stored in a couple hundred pounds of rock is puny compared to the number of BTUs that went up the chimney during a burn cycle.

Here's photo from Tulikivi's website that illustrates this nicely:



By their numbers, soapstone transfers heat at about 1/9 the speed of cast iron, but stores about 2x the heat per gram. Cast iron has about double the density of soapstone, so the same volume would weigh twice as much and store roughly the same amount of heat.

That little girl would be having a Learning Experience if she was doing that to a cast iron unit- she's not being burned because the heat from that raging fire is mostly going up, not into the room.

Edit: Please don't take away "Soapstone is a bad thing to put on a woodstove" from this. The properties of a material are usually easy to understand; the properties of a system using that material are often a lot harder to grok. For this reason, I'd trust reviews from people who have stove X more than the general concept of 'soapstone doesn't transfer heat that well', which is true, but not the whole story of how a complex, engineered appliance works.