Catalytic Combustor Question

[Rhone]

Essentially that is what Hearthstone does with the Morgan and Clydesdale inserts. They are metal stoves with the firebox lined with soapstone bricks. I think ya could do that with any stove. Some will say that other stoves weren't certified with soapstone in them but I contend that they weren't certified with red oak burning in them either.

I don't know, the Clydesdale & Morgan are soapstone inside cast iron outside, whereas in this situation it would be cast iron/steel inside w/soapstone outside. I have the Clydesdale, when I see a firebox with firebrick it looks like the firebrick rests directly against flat walls. The Clydesdale, it's walls have air channels stamped into them that keep the soapstone floating so it doesn't have complete contact. I included pictures, straight from my manual I added the yellow to it, ignore the real arrows which are pointing to a couple allen wrench screws, and the back levelling bolt. The one I drew the arrows shows the air channels in the back, the one with the spots identifies each stamped pocket or bump to keep the soapstone from having full contact, there's more than is shown. I find it interesting the floor is big air pockets minimizing cast iron contact with the soapstone and the sides & back are the reverse, a lot of cast iron contact with a little bit of air channels. I don't know why they'd do that unless having the soapstone have direct contact was a problem. Hmm... this may answer the difference MSG and I talked previously and his soapstone stove prefers ash and mine doesn't. With all those little air pockets I have beneath my soapstone that's dead air space and insulation, he doesn't have it and his likes some ash.

I would think you could surround your unit with soapstone but keep some space at least, the steel stoves I've had in the past always started to warp a little over time, I think that's why every soapstone unit I've seen uses cast iron as their metal. As for having the soapstone allow direct contact, I'm not really sure about that. All the channels in the Clydesdale make it look like there's a problem having that configuration, not to say they didn't stamp all those pockets and channels and things for another reason, or maybe I've not been paying attention and firebrick units also have them.

 

[Todd]

We we would engage the catalytic combustor during the evening hours when the inside temperature hit 500 degrees, and then go to bed. By morning, the temperature inside the stove sometimes dropped below 500 degrees, but of course, the catalytic combustor was still engaged.

That's why I love this stove - "sometimes" it's not still raging hot in the morning and is a balmy 350-400 degrees instead of 500 degrees.

You are perfectly fine - the surface temperature on a Fireview only needs to hit 350 to engage the cat initially - due to the damped heat transfer with the soapstone, 350 on the surface means it's much much hotter inside. (as opposed to steel/iron where you'd want to see a higher surface temperature to be sure you can engage the cat)

Towards the latter half of your burn cycle, all the volatile wood gases that were being burned by the catalyst are long gone so even if it cools down to room temperature with the cat engaged, no harm is done. Just bypass and get the surface temperature back up over 350 if it's not that hot when you reload - this will keep it running at peak efficiency and ensure the gases in the new wood reload will burn nicely.

-Colin

I think you have the stove top temp wrong. Manual states 250 will indicate a 500 degree temp inside. But I also have a probe thermometer and I reach 500 way before the stove top reaches 250 on a cold start. Soapstone is slow to react.

 

[Todd]

Well there it is ............

Your right , you got me .


I heat my 1800 sf home 100% with wood heat ,
Temps drop below 0° for weeks last year. ( -10° / -20° )
I get 8-10 hour burn times + heat after the fire goes out.
The house never gets over 78° ( average 74° ) all winter
The house never drops below 65° upstairs all winter.
And here is the big one .........I used 3.7 cords of wood doing it. ( 4 cords )


Not too hot , not too cold , long burn times and 3.7 cords of wood used.


I dont see a problem with that.

yet I see nothing but defensiveness when shortcomings are discussed

So what were the shortcommings?
defensiveness ? I was stating information and clearing up miss information and providing the differences.
I think your blowing this way out of proportion and stretching information. I didnt cut down soapstone stoves or say anything bad about them or mentioned any shortcomings.

Hey Roo,
My stove is better than your stove! :coolgrin:

 

[cbrodsky]

I think you have the stove top temp wrong. Manual states 250 will indicate a 500 degree temp inside. But I also have a probe thermometer and I reach 500 way before the stove top reaches 250 on a cold start. Soapstone is slow to react.

Todd - you are absolutely right - I should have checked the surface thermometer before answering.

Interesting to hear you have a probe in there - I also found last season that I could often engage the cat at 200 surface temperature if the fire was raging good, but I generally don't push it. Not surprised by your findings.

What kind of probe are you using, and how did you thread the probe in? One of these days I'd like to get a pre-post cat temp just to squeeze the last bit of efficiency out of it.

-Colin

 

[Roospike]

@*%$

 

[cbrodsky]

Essentially that is what Hearthstone does with the Morgan and Clydesdale inserts. They are metal stoves with the firebox lined with soapstone bricks. I think ya could do that with any stove. Some will say that other stoves weren't certified with soapstone in them but I contend that they weren't certified with red oak burning in them either.

I find it interesting the floor is big air pockets minimizing cast iron contact with the soapstone and the sides & back are the reverse, a lot of cast iron contact with a little bit of air channels. I don't know why they'd do that unless having the soapstone have direct contact was a problem.

I would think you could surround your unit with soapstone but keep some space at least, the steel stoves I've had in the past always started to warp a little over time, I think that's why every soapstone unit I've seen uses cast iron as their metal. As for having the soapstone allow direct contact, I'm not really sure about that. All the channels in the Clydesdale make it look like there's a problem having that configuration, not to say they didn't stamp all those pockets and channels and things for another reason, or maybe I've not been paying attention and firebrick units also have them.

Could the floor difference be to help minimize floor protection requirements? Woodstocks use a thin offset sheetmetal plate that sits about an inch below the base of the firebox - without this you apparently get way too much heat into the floor.

I would also think that too much direct contact could be an issue depending on the relative coefficient of thermal expansion. Not sure how that compares among those materials.

-Colin

 

[Sandor]

That why the stove is rated at 97,000 BTUs at a 3.0 cf fire box and there are other stoves with a 3.0 cf fire box that are rated at 55,000 - 70,000 BTUs . The MASS of the STEEL is the missing key with the comparison of steel stoves.

[

Roo,

I am really not sure how you create over 40 thousand BTU's from a 100 pounds of cold steel. I do believe that may violate the laws of physics, and certainly thermodynamics.

I can buy a line about stove efficiency and design, but come on.

I believe 100 percent that you are a paid spammer. Why are you hyjacking threads about Catalytic Combustors? And I certainly agree with Colin that you are biased to the point of absurdity.

 

[cbrodsky]

That why the stove is rated at 97,000 BTUs at a 3.0 cf fire box and there are other stoves with a 3.0 cf fire box that are rated at 55,000 - 70,000 BTUs . The MASS of the STEEL is the missing key with the comparison of steel stoves.

[

Roo,

I am really not sure how you create over 40 thousand BTU's from a 100 pounds of cold steel. I do believe that may violate the laws of physics, and certainly thermodynamics.

I can buy a line about stove efficiency and design, but come on.

I believe 100 percent that you are a paid spammer. Why are you hyjacking threads about Catalytic Combustors? And I certainly agree with Colin that you are biased to the point of absurdity.

Yea, that made no sense to me either - mass of the steel has nothing to do with heat output.

From a thermal conductivity perspective, steel of 3/8 or 1/2" is going to conduct heat like crazy compared to stone of similar thickness. The conductivity value of steel/iron is already so high that increasing the thickness 1/8" does nothing to significantly alter that relationship, as noted earlier. It's an order of magnitude higher than stone. Good in some applications, but no getting around the fact that it requires one to burn faster and throw off more heat from an identically sized firebox to maintain the same internal fire temperature. When you see soot on a stove door, it's #1 sign the user has been damping down too much in order to try to extend the burn time too far - Roo's picture of his own stove shows this happening and I'm assuming in his case, it's not due to bad wood. (can't speak for other random internet pictures...) He explicitly mentioned getting overheated in his house running a 600 deg. surface temperature - that doesn't surprise me at all. That's how that type of stove is made to run - it's designed to pump out much higher BTUs than a similarly sized stone stove could ever accomplish; it's design strength is not running on really long slow burn intervals. Not saying one is better than the other - just depends on what the user wants.

Even if he's trying to argue residual heat capacity in that stove is a big advantage, it is negligible. Assume the stove is 100 lbs heavier - at 0.12 BTU/(lb*degF), at 500 degrees in a 75 degree room, the total heat stored in an extra 100 lbs of steel is about 5000 BTUs.

Cast iron runs about 0.16 BTU/(lb*degF) and soapstone at 0.23 BTU/(lb*degF). So in a ~450 lb soapstone stove, you hold at most about 44,000 total BTUs when up to temperature; that would be about 23,000 total BTUs in a steel stove. It's 2X but nothing night and day difference like the thermal conductivity, which drives the fundamental differences in how these stoves behave. To be fair, owners of stone stoves sometimes overbill just how much heat is stored in these stoves

The main thing I suspect you get with the thicker plate is less warpage, the historical weak link in such stoves. I am sure it is a very sturdy and well made stove as a result of that enhancement. But it won't deliver the same benefits (or drawbacks) that a soapstone stove does, no matter what the salesman-like claims made on these forums would suggest.

-Colin

 

[cbrodsky]

That why the stove is rated at 97,000 BTUs at a 3.0 cf fire box and there are other stoves with a 3.0 cf fire box that are rated at 55,000 - 70,000 BTUs . The MASS of the STEEL is the missing key with the comparison of steel stoves.

[

Roo,

I am really not sure how you create over 40 thousand BTU's from a 100 pounds of cold steel. I do believe that may violate the laws of physics, and certainly thermodynamics.

I can buy a line about stove efficiency and design, but come on.

I guess you already made up your mind before you posted without reading the thread .........AGAIN.

Your going to have to take the 97K rating up with Pacific Energy . The stoves rated at 60K BTU with a 3.0 firebox ..... again , your going to have to take it up with them.
If you would take the time to READ Sandor you will see the post i replied to and why i replied.

Sandor ....... I had asked you to post photos and or other information of your stove ash pan and grate system......NOTHING .
Than you come here and call ME a "paid spammer" . Nice , took a lot of home work and effort on your part to come up with that. , I'm impressed.

You actually believe manufacturer BTU specs and would reference them in an argument? Those are rather thoroughly debunked on this site. I believe as a class, for a given firebox size, a steel stove does have much higher max BTU than stone as noted above. The drawback is lower min BTUs while in clean burn, no matter what manufacturer tells you. Each user needs to decide what is more important to them - there is no free lunch in thermodynamics.

Honestly, the constant cheerleading of PE Summit into nearly every thread on this forum with no acknowledgement of relative pros/cons really does get tiresome. It's cute for a while, but it's over the top at this point.

BTW, I have no problem pointing out that the Woodstock Fireviews do not even have an ashpan. If someone has to have a 3 c.f. firebox and an ashpan, they will not find it at Woodstock. It's a trade-off I was willing to make for the other benefits of the stove.
If I did get an ashpan, I'd go for the grate-type, but that's just me.

-Colin

 

[Roospike]

$*%#

 

[webbie]

People, People.....!

Way over the line!

What do you think new forum members are going to think of your rants? They can't put up with all that just to get a little info. We all know about "my dad can lick your dad", but let's keep both sides of that debate in another forum (off hearth.com)...

Blantant commercialism is not welcome either.

On the other hand, I'm pleased to see folks who are happy with their choices! But being truly happy usually means YOU DON'T want everyone else to know about your great stove - after all, when everyone has one they won't be as special.