Vermiculite vs. Firebrick vs. Soapstone

[heydan]

I noticed that my new Regency I2400 has firebrick all around the firebox except for the top surface which is vermiculite. I asked the company about this and they told me their warrantly claims dropped a lot when they switched to vermiculite for the top surface instead of firebrick all around. From this I conclude that vermiculite is more durable when it comes to withstanding the very high temperatures at the top of the firebox.

So now my next question is why not use vermiculite everywhere? Is it a lot more expensive than firebrick? Does it have some other drawback such as not insulating as well or not being able to withstand the weight of a load of wood on the bottom of the firebox? What is the difference between vermiculite and firebrick in practice?

Part of the reason I want to know is that I know the firebrick will eventually wear out and need to be replaced. When that time comes, would there be any reason to replace the original firebrick with more vermiculite?

On a related note, would it be reasonable to replace any of the firebrick with soapstone bricks to increase the thermal mass of the stove? The company said I shouldn't: "The firebricks do protect the metal firebox and yes helps keep the heat needed for combustion to burn the wood thoroughly. They do not act like soapstone and radiate heat after the fire has burned down. The Stove has not been tested or certified to use other types of Bricks or soapstone and could cause early signs of wear and could also void the stoves warranty."

What do you all think? What might be the result of replacing ordinary firebrick with either vermiculite or soapstone?

 

[wg_bent]

I noticed that my new Regency I2400 has firebrick all around the firebox except for the top surface which is vermiculite. I asked the company about this and they told me their warrantly claims dropped a lot when they switched to vermiculite for the top surface instead of firebrick all around. From this I conclude that vermiculite is more durable when it comes to withstanding the very high temperatures at the top of the firebox.

So now my next question is why not use vermiculite everywhere? Is it a lot more expensive than firebrick? Does it have some other drawback such as not insulating as well or not being able to withstand the weight of a load of wood on the bottom of the firebox? What is the difference between vermiculite and firebrick in practice?

Part of the reason I want to know is that I know the firebrick will eventually wear out and need to be replaced. When that time comes, would there be any reason to replace the original firebrick with more vermiculite?

On a related note, would it be reasonable to replace any of the firebrick with soapstone bricks to increase the thermal mass of the stove? The company said I shouldn't: "The firebricks do protect the metal firebox and yes helps keep the heat needed for combustion to burn the wood thoroughly. They do not act like soapstone and radiate heat after the fire has burned down. The Stove has not been tested or certified to use other types of Bricks or soapstone and could cause early signs of wear and could also void the stoves warranty."

What do you all think? What might be the result of replacing ordinary firebrick with either vermiculite or soapstone?

Well, personally, I wouldn't mess with what the company said.

I've replaced bricks in my stove with a slightly different brick, but that doesn't seem a problem. Even if you did replace the bricks with soap stone, there is not that much of it in a stove designed to have bricks, so thermal mass wouldn't really increase that much over the heavier of the two types of firebrick. Plus you risk the problem of changing the way the stove transferrs heat.

 

[Eric Johnson]

Vermiculite is pretty cheap. The only kind I've ever seen is granular. Sounds like you're talking about some kind of pressed board product.

 

[webbie]

I noticed that my new Regency I2400 has firebrick all around the firebox except for the top surface which is vermiculite. I asked the company about this and they told me their warrantly claims dropped a lot when they switched to vermiculite for the top surface instead of firebrick all around. From this I conclude that vermiculite is more durable when it comes to withstanding the very high temperatures at the top of the firebox.

So now my next question is why not use vermiculite everywhere? Is it a lot more expensive than firebrick? Does it have some other drawback such as not insulating as well or not being able to withstand the weight of a load of wood on the bottom of the firebox? What is the difference between vermiculite and firebrick in practice?

Part of the reason I want to know is that I know the firebrick will eventually wear out and need to be replaced. When that time comes, would there be any reason to replace the original firebrick with more vermiculite?

On a related note, would it be reasonable to replace any of the firebrick with soapstone bricks to increase the thermal mass of the stove? The company said I shouldn't: "The firebricks do protect the metal firebox and yes helps keep the heat needed for combustion to burn the wood thoroughly. They do not act like soapstone and radiate heat after the fire has burned down. The Stove has not been tested or certified to use other types of Bricks or soapstone and could cause early signs of wear and could also void the stoves warranty."

What do you all think? What might be the result of replacing ordinary firebrick with either vermiculite or soapstone?

Bricks of pressed ceramic particles (perlite, vermiculite) are quite fragile but work well in areas that you are not going to poke wood into. Regular firebrick is much more durable in terms of physical shock.

As mentioned, you should leave things in factory condition. I know that lots of us like to tinker, but this is not the place. You will not get any more "MPG" from your stove by such mods.

 

[Sandor]

I owned two Regencies, the 2400 I burned for a decade and the larger model (3100?)I burnt for a year.

Both had a very dense type concrete roof, that was very durable. If the vermiculite gives up too soon, order the older stone roof. These were heavy pieces.

The firebrick lasted me about 5 years before it started to crumble. I think the replacements were about 50 bucks for the whole stove.

That stove can go from stone cold to blazin hot in short order. I would not think twice about replacing the fly weight firebrick with soapstone. I think it would help it out alot. I would do it to even out the incredible temperature swings that I experienced, and the thermal mass can't hurt either.

 

[heydan]

Thanks, Craig. You've explained why there's only vermiculite blocks on the top -- they're good for withstanding the intense heat up there but would crack under the physical impact of the logs that the other sides are subjected to.

Thanks, Sandor. You've stated exactly the reasons I'm tempted to tinker with the manufacturer's design. I could replace the firebricks with soapstone bricks like these: http://www.rumford.com/store/soapstone.html The idea would be to try to moderate the extreme temperature swings. I'd be emulating the design of soapstone-lined fireplace inserts like this one: (broken link removed to http://www.hearthstonestoves.com/wood_stoves/morgan/)

However, as Craig said, it might not be smart to tinker with the manufacturer's design. If such a simple change were really an improvement, wouldn't they have done it already?

 

[heydan]

I notice that this page:

http://www.cjshomedecor.com/acatalog/Morso_Model_3440_Wood_Stove.html

mentions a stove that has "a cast iron firebrick-lined firebox but incorporates beautifully smooth soapstone from Finland for its exterior panels."

So in this case even when building a stove that has soapstone on the outside they still used firebrick in the firebox. That makes me think there must be a reason to prefer firebrick over soapstone inside the firebox.

 

[wg_bent]

I notice that this page:

http://www.cjshomedecor.com/acatalog/Morso_Model_3440_Wood_Stove.html

mentions a stove that has "a cast iron firebrick-lined firebox but incorporates beautifully smooth soapstone from Finland for its exterior panels."

So in this case even when building a stove that has soapstone on the outside they still used firebrick in the firebox. That makes me think there must be a reason to prefer firebrick over soapstone inside the firebox.

The way soapstone is used on that stove is completely different from it's use in something like a Hearthstone or Woodstock.
The Morso stone isn't in contact with the fire, so doesn't absorb as much heat in that application. It works somewhat, but not like the soapstone interiors. Not like a Tulikivi either. A 3440 will heat up quickly and produce usable heat like a steel stove, but the soapstone will stay somewhat warmer than the Cast iron version longer.

 

[heydan]

Yes, good point. Here's a better picture of the Moreso stove:

(broken link removed to http://www.morsoe.com/us/3450.htm)

It's just a cast iron stove lined with firebrick with some soapstone stuck on the outside.

 

[heydan]

When I look at the manual for the Hearthstone Clydesdale:

http://www.hearthstonestoves.com/wood_stoves/clydesdale/

I see that the soapstone bricks are laid right into the metal firebox, just like the firebrick bricks are in my Regency I2400. The only difference is that the Clydesdale is cast iron and my Regency is steel. But this example makes me think maybe I could use soapstone bricks in my Regency instead of firebrick.

 

[heydan]

I see this question has been visited here before (but without a conclusive answer):

https://www.hearth.com/talk/threads/1973/

 

[heydan]

I found a relevant comment here:

https://www.hearth.com/talk/threads/196/

Firebrick is very different than soapstone, firebrick is designed to reflect heat and hold nothing. It's even worse than normal brick for holding heat. Its purpose is to reflect heat back into the fire to get higher temperatures so the fire burns better and also to protect usually the steel from getting too hot. It allows a very responsive fire, as it gets the heat out of it and into the living area.

Soapstone is the opposite. Instead of being a reflector it's a battery for heat (natures most heat holding and transferring solid material on the planet). You light a fire, and you have to wait for the soapstone to "charge" up before you feel heat. Likewise, if you lower the air control you have to wait for the soapstone to "discharge" its stored heat before it catches up with your lower setting. It's very different than what you're used to if you've never experienced soapstone, and rather comparitively expensive.

Either way you shouldn't mess with the design of your unit, soapstone has the properties you're looking for and I think you'll get very little of its benefits by retrofitting. Units designed around soapstone take advantage of it.