# Materials used to line fireboxes - a test



## precaud (Feb 1, 2009)

From some discussion in another thread, I thought it might be useful to take a look at the various materials that are used to line woodstove fireboxes. There are basically four that I know of: Cast iron, dense firebrick (the heavy, yellow ones used in most pre-EPA stoves), porous firebrick (the lightweight ones used in some modern stoves), and Vermiculite panels (such as Skamol, used in many European stoves).

What these materials have in common is that they are, more or less, rugged enough to withstand the temperature swings (called thermal shock) and survive having wood jammed into them from time to time (mechanical shock).

What differs greatly is how readily heat passes through them. The measure of this is called Thermal Coefficient, K for short. A high K says the material readily collects and stores heat. A low K says the material is a good insulator, and resists the flow of heat through it.

Here is the thermal coefficient of these materials at 1000ºF _per inch of thickness_:

Cast iron : 150+ (from 55 at 200Fº)
Firebrick (heavy, yellow) : 14 (5.5 for a typical 2.5" thick brick)
Firebrick (light, insulating) : 1.1 (0.88 for a typical 1.25" thick brick)
Skamol V-1100 Vermiculite slab : 1.10 (slabs are typically 1" thick)

As you can see, cast iron and the heavy firebricks are poor insulators. It's no coincidence that they were widely used in pre-EPA stoves, when designers were trying to pull as much heat as they could OUT of the firebox. The lightweight firebrick is the better insulator by far, with the vermiculite a close second. And while all of them lose some of their insulating value as temps increase, cast iron is the worst, increasing by three times. No wonder it warps.

So if you want clean combustion AND high efficiency, you want a stove that uses the light firebricks.

Here's an excerpt from an article titled "The Straight Facts Concerning Refractories" by a company who designs and builds gas-fired forges:
_
Ceramic Blanket, Ceramic Fiberboard and Lightweight Insulating Firebrick are classified as Insulation, while Dense Ceramic Firebrick is NOT.

The insulating refractories have Low Thermal Conductivity, which means heat does not readily pass through them. The heat is reflected back into the chamber instead, creating a super efficient firebox.

Dense Ceramic Firebrick on the other hand, has a High Thermal Conductivity, which means heat readily passes through it, instead of "insulating" the chamber, it acts as a heat sink, absorbing heat and radiating it off through the shell. Dense Ceramic Firebrick, by it's very nature, ROBS a Forge of valuable heat. It's cheap and a very poor choice as a liner material.
_


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## begreen (Feb 1, 2009)

Durability is also a factor in fireboxes. It took almost 20 years for my Jotul 602's _inner_ burn plates to warp and crack. That's pretty durable and the servicing of them was fairly easy. The outside castings of the stove still look like new.


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## precaud (Feb 1, 2009)

That would come under thermal and mechanical shock, methinks.


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## precaud (Feb 1, 2009)

Here's a paper which deals in detail with the characteristics of refractory materials:
http://www.wipo.int/pctdb/en/wo.jsp?IA=GB2001000470&DISPLAY=DESC

Sure, reading this stuff makes your eyes bleed and head spin, but this is true of much scientific analysis.

Here's why this topic interests me so much. Higher efficiency and cleaner combustion have become the focus in all heating appliances, not just woodstoves. Do we want cleaner and more efficient woodstoves? Sure we do. If there was a simple way to make your stove better, would you do it? Sure you would. Maybe not immediately, but eventually.

If you look across the whole field, ceramic composite materials are at the heart of the innovations leading to improvements in nearly every respect. So it seems to me that, rather than go retro and go back to cast iron or heavy firebrick liners, we need to make the porous ceramic materials more rugged so they can last longer. I see two possible angles that could be simple enough to be done by a typical stove owner:

1. Improve early EPA stoves by upgrading the liners.
2. Modify lightweight firebricks to make them more durable AND increase their reflectance at the same time.

What I'm looking for are others who see the value in this and might want to take it up too. If you want to champion the value of iron and fireclay, please do it in another thread. If all you want to do is throw another split on the fire and pop another Bud, this thread is not for you. Let's keep this clean and positive.


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## precaud (Feb 4, 2009)

I got the sheets of Zircar RS-1200 today.
http://www.zrci.com/rs1200.htm
This is very cool stuff. Much denser than I had imagined - much denser than the ceramic fiber boards used for baffles. A 24x24x1/2" sheet weighs 22.5 lbs. It is easily rugged enough for use in a stove. And the stuff is pure white - exactly what I think is best for a liner, as so much of the energy inside the firebox is radiant not convective.

My first experiment with it will be to make replacement liners for the cast iron ones in my Jotul F602 and see what difference it makes. I'm trying to dig up another magnetic thermometer so I can monitor temps on the side and the top of the stove. The local stores are all out of them.


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## johnn (Feb 4, 2009)

I`ll keep your thread handy to see how it goes and sponge off your learning curve. Don`t expect much from this end , as the material you read and understand may very well need an interpretor for me.      once I decide what to replace my insert with, I will have an old steel body to tinker with for the garage,,,just don`t try to talk me into a "home-made secondary"


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## precaud (Feb 5, 2009)

ml said:
			
		

> Once I decide what to replace my insert with, I will have an old steel body to tinker with for the garage,,,


Ah, the perfect specimen for such a project!


> just don`t try to talk me into a "home-made secondary"


Somebody else might, but not me  

It turns out the RS-1200 is really expensive stuff, about $63 per sq ft. Ouch. But it's perfect stuff to test my theory, and if it works we can look around for more cost-effective material.


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## johnn (Feb 5, 2009)

precaud said:
			
		

> ml said:
> 
> 
> 
> ...



  Call 911, we`ll need a large compression bandage! Keep looking. Read somewhere in forum where cement board was being tested or used for a firebox??
  Yesterday I came across a thread by ..Peter B.. with pic`s of home-made secondary`s, very impressive job. Might rethink my position on trying it! Materials and tooling very accesible if not free..even stainless..just cost me time and possible pride.


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## Peter B. (Feb 5, 2009)

ml said:
			
		

> Once I decide what to replace my insert with, I will have an old steel body to tinker with for the garage,,,
> 
> <snip>
> 
> Yesterday I came across a thread by ..Peter B.. with pic`s of home-made secondary`s, very impressive job. Might rethink my position on trying it! Materials and tooling very accesible if not free..even stainless..just cost me time and possible pride.



Actually, this is THE thread on addition of secondaries to steel box stoves:

https://www.hearth.com/econtent/index.php/forums/viewthread/31420/

It's worth the effort, sez I.

Peter B.

-----


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## johnn (Feb 7, 2009)

>
  Yesterday I came across a thread by ..Peter B.. with pic`s of home-made secondary`s, very impressive job. Might rethink my position on trying it! Materials and tooling very accesible if not free..even stainless..just cost me time and possible pride.[/quote]

Actually, this is THE thread on addition of secondaries to steel box stoves:

https://www.hearth.com/econtent/index.php/forums/viewthread/31420/

It's worth the effort, sez I.

Peter B.

-about:Tabs----[/quote]

  Trust me I got that one handy! Maybe we`ll have a well priced and suitable liner material mid year.


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## EddyKilowatt (Feb 7, 2009)

precaud said:
			
		

> I see two possible angles that could be simple enough to be done by a typical stove owner:
> 
> 1. Improve early EPA stoves by upgrading the liners.
> 2. Modify lightweight firebricks to make them more durable AND increase their reflectance at the same time.



How about insulating behind cast iron liners?

The 3/8" airgap between the stove wall and the cast iron liner plates on my Jotul 8 (pre-EPA) probably wasn't too bad an insulator, right from the factory.  

Never one to just leave things alone, I took the plates out and filled that air space with ceramic wool (leftover stainless chimney liner wrap), on all 3 sides of the firebox.  

I did this pretty early in my experience with the stove, so it's a little hard to compare the before-and-after... but I would say the stove definitely holds a fire better (especially a small one) and seems to burn cleaner and hotter.

Time will tell what those liner plates think about having the heat-flow path behind them cut off.  So far I'm not seeing any cracking or warping (knock wood).

Eddy


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## precaud (Feb 7, 2009)

Eddy,
It's great that you're experimenting. What you've done is similar to Jotul's approach; cast iron liners with a thin layer of ceramic wool between the liner and the shell. It is an improvement over an uninsulated iron liner, no question, but I think there is a much better way. That's the first comparison I'll be making, using my Jotul F602 as the guinea pig. Stay tuned.


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## precaud (Feb 7, 2009)

Here are some photos you might find interesting.

The first two are the left-side liner from my Jotul F602, which is sidelined this heating season, with an injury, you might say  

The liner is cast iron, approx. 8" x 15", with a 1/4" thick piece of ceramic wool on the inside. Weight is just under 8.5 lbs.

Jotul uses this type of liner on the sides of many of their stoves.

As you can see, this stove has problems burning cleanly in the back half of the firebox. The design of the air supplies has something to do with that. But the less-than-optimal insulation of the firebox plays a big role.

The third photo is a piece of Zircar RS-1200 material shaped and ready to install. Weight is 4 lbs.

This material is a joy to work with (apart from the dust...). Imagine gypsum board but much more rigid and dense. It works easily with standard woodworking tools.


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## Doctuh (Feb 7, 2009)

Oddly enough just took this pic of the inside of my firebox for another thread. I believe this is light firebrick.


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## begreen (Feb 7, 2009)

cmon precaud, show us how she burned with the gold plated innards.


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## precaud (Feb 7, 2009)

Doctuh said:
			
		

> Oddly enough just took this pic of the inside of my firebox for another thread. I believe this is light firebrick.



I can't tell - your glass is too dirty


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## precaud (Feb 7, 2009)

BeGreen said:
			
		

> cmon precaud, show us how she burned with the gold plated innards.



At $63 a sq ft, it better be gold!

It may be a few days before I install it, we have a cold front heading in tonight and the little F602 can't handle 1000 sq ft, even with Zircar the Magnificent inside.


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## begreen (Feb 7, 2009)

This is an interesting project. Can't wait to see how it turns out.

 I also thought it was interesting to see the burn pattern in the F602CB. Our older 602 didn't show that. It burned pretty cleanly in the back


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## precaud (Feb 7, 2009)

BeGreen said:
			
		

> I also thought it was interesting to see the burn pattern in the F602CB. Our older 602 didn't show that. It burned pretty cleanly in the back


Yeah, they burn completely differently. I think with this new material and adding a few holes to the secondary manifold in the far back, it will burn hotter and cleaner.


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## precaud (Feb 8, 2009)

Well the longterm weather forecast isn't _that_ bad so last night I took down the X33 (BTW, the pipe looked nice and clean, the X33 lives up to its promise) and installed the F602 with new liners in it. As recommended by Zircar, I did a couple small burns to drive the moisture out of the material. Today I'll do the first full burns.

But first I gotta put this F602 liner test in context. The main problem with the F602 is not the liners. It is the air systems, particularly the adjustable one on the door. This has to be the most stupid, ineffective design I have ever seen in any EPA stove. Besides being too hot to touch when the stove is in use (doh!), it directs air into the stove at a 35º angle to the left. The only way around this and get an even burn is to either keep it fully closed (which you can only do with extremely high draft) or full open (almost no draft, the Florida bungalow syndrome). All Jotul needs to do to fix this is redesign the small manifold on the inside of the door behind the slide control. It's not something us mortals without foundries at our disposal can fix. Add to this that there is NO secondary air introduced into the back HALF of the firebox, and it's easy to understand the dirty burn pattern, and why it always burns from bottom left to upper right, and always leaves unburned wood in the right rear corner. Changing the liner material is not going to change this.

Is this what we're paying $900 for? (That's what F602's sell for around here.) As a former designer/manufacturer (not of stoves), it really frustrates me to see the performance of otherwise nice units totally compromised by such simple things. I think it is important to shine a bright light on such things in public forums. Otherwise those manufacturers will continue to get away with delivering incomplete designs to us with refuse like this in them. The fact is, this design should have never gotten out of the door at Jotul. And whoever OK'ed it should be forced to heat their home with one for the rest of their days.

Enough ranting. On with the test.


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## precaud (Feb 9, 2009)

After placing thermometers on the top plate and side panel, I burned three loads today with the new liner, monitored temps, watched it burn, and went outside to view the stack exhaust. Yes, some improvement was noted, but nothing night-and-day. Tomorrow I'm going to put the iron liners back in, do the same thing, and compare numbers. I can't give it more time right now, because the F602 simply does not keep my 1,000 sq ft basement warm enough, and I work down there. More tomorrow.


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## precaud (Feb 9, 2009)

Well perhaps my assessment was a bit too cautious yesterday... there is absolutely no question that this stove burns cooler and dirtier with the cast iron liners back in. It's gone back to being an underwhelming heater. Details to follow tonight.


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## precaud (Feb 10, 2009)

Before I give the numbers, a few words about the process.
Each day's burn started from a cold stove, kindling fire to get started, then a layer of 1-2" pieces to get a coals bed and get the temps up. Then start the actual burn loads. Three were done each day over about 5-1/2 hours. Each load was three pieces, about 12" long and 4" diameter. As is normal, the supplementary air control (Jotul calls it the primary air but it isn't) was opened some until a brisk fire was burning, then slowly backed off until it burns with the control closed or just slightly open  and all primary air is supplied by the airwash. (I've written in previous posts about the F602 primary air so I won't repeat it.) The load then burns without changes unless needed, see below. Today's run with the cast liners was 10-12º colder outside so the chimney draft was a little stronger, which favors the cast a bit.

About the numbers: I calibrated the two Condor thermometers at 300º, which is about the highest my Fluke contact probe goes. They track very well until above 500º, where one reads increasingly lower than the other. I put that one on the top plate since it gets hottest there. The other one was placed in the middle of the left side plate, right on top of the lion. So the absolute numbers above 500 aren't important; it's the relative difference that matters. The numbers are the maximum temps reached during that load. 

Cast iron liners
Load 1 :  550 Top...370 Side
Load 2 :  670 Top...430 Side
Load 3 :  730 Top...450 Side

Zircar refractory liners
Load 1 :  650 Top...440 Side
Load 2 :  750 Top...500 Side
Load 3 :  770 Top...510 Side

So there it is. There is no question that with the ceramic liners, the stove warms up more quickly, burns hotter, and puts out more heat. And you can feel the difference in the room, and smell it too. Cast iron puts out a peculiar smell when temps reach a certain point. The real shocker is how much hotter the stove sides were. So much for the theory that the cast iron liner has better heat transfer.

At least four times during each load, I went out and observed the stack. With the cast iron, there was visible smoke all but one time. With the ceramic, there was smoke at the beginning and at the end of each load, but none or barely visible for most of the burn. The hotter temps come from a cleaner burn.

See the pics below. The first one is the right-side iron liner. It's dirtier than the left side iron liner (see it's pic a few posts above) because of the air system design. Compare it to the second pic of the ceramic right side liner. As you can see, it burns cleaner, and further back into the stove. You can clearly see the arc of the primary air wash circulation, and the secondary burn path at the top, neither of which are visible on the iron liner. The third pic is the left-side ceramic liner. Compared to the cast of that side , it too burns cleaner and further back. And the one super-clean spot shows how the air channels toward the left, as I've said. It's all in the burn pattern.

Totally unexpected was the change in how the wood burned. With the iron liner, after the temps peaked, the fire intensity would drop off and go towards a smoulder condition, due to little air and lower temps in the back of the stove. I had to rake everything forward and open the air control a little to get them to burn fully. But with the ceramic liner, to my great surprise, all three loads burned all the way to the back without changing a thing. The higher temps in the firebox are responsible for this.

Not only that, coaling was a problem with the iron liners. I had to burn the coals down after the second and third load before reloading. With the ceramic liners, I did not have to burn off coals. This was a big surprise.

Conclusions from this experiment:
: As suspected, cast iron is a poor choice for liner material, even if it is insulated.
: Ceramic refractory is a superior lining material, giving better insulation AND better heat transfer through the walls.
: In every way that matters, a hotter firebox makes for a better stove, giving cleaner burning and less smoke, more heat output, higher efficiency, and less coaling.

I'm going to put the ceramic liners in again in the morning and rerun the test with the cooler outside temps, like we had today.

Pretty solid results, I'd say.


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## markleyh (Feb 10, 2009)

Wow!

I say, old boy, you've done it, you've really, really done it!

Bravo!!

Am I nuts to think about what King Zircar could do for my Fireview???!

Herbert


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## precaud (Feb 10, 2009)

At $63/sq ft., King Zircar extracts quite a price. I'd bet there are more cost-effective choices. Is it firebrick? What are the dimensions and color? A high-alumina firebrick (white color) should do as well as the good King.

Added: The point of this experiment is not to show that the RS-1200 is the best material for a liner. It's probably the best stuff in 1/2" thickness. And it's clearly better than cast iron, which is as bad as it gets. (Heck, the glass door on your stove is a much better insulator than iron is.) But most stoves use thicker lining material, 1" to 1-1/4". If you replace the liner, you want to use the same thickness so the firebox geometry isn't changed.

There are firebricks that have characteristics as good as or better than the RS-1200, for alot less money. It would be great if someone who has a stove with the darker-colored brick would experiment and replace it with the whiter brick. If I had such a stove, I'd do it. But I don't. Anyone game? I'll help with finding the right brick.


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## Woodrat (Feb 10, 2009)

------I love to see threads like this-goes to show that not all good ideas come from the corporate think tanks. FWIW, I have been able to get very similar results with my old Dragon Nashua by double bricking the firebox and going another tier high on the sides-- also put some firebrick on top of the baffle 
------Net result of this tinkering has been to increase overall stove operating temps by about 100 degrees-- extend the burn time-- leave me with very little in the way of  an overabundance of coals (where I used to sometimes have 3-4 inches- now I still usually have 200 degrees or more in the AM, the stove restarts rapidly and the bricks are always clean!!
-----My uneducated “take” on this is that the increased mass of the stove due to all the extra firebrick helps hold the temps up in the stove (more by moderating the tempereture swings than by insulating the firebox). I am more than happy to be generating more heat, keeping it longer, & most importantly--doing it with 1/3--to ½ less wood than I burned in years past.
----I have other changes I plan as time and money allow (secondary air etc)
----Admittedly, changing the firebox size this much may not be a workable option for many-- the Nashua was a massive stove to begin with, and even with the extra brick, it’s probably still a much bigger firebox than most stoves.  All I can say is that it WORKS and didn’t involve spending a ton of money (also would have been easy to “undo” in the event that it didn’t work out. These are just standard  firebrick “splits” that I’m talking about.(under $2 each)

Best wishes, Woodrat


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## precaud (Feb 10, 2009)

Glad to hear of your similar good results, Woodrat. Your stove is big enough to eat my F602 for breakfast! The only comment I'd make is your take about the increased mass. The concept of "holding heat" doesn't apply to what is needed in a firebox. High insulation and low mass is best. Doubling up the brick doubles the insulation and that's making a big difference. But all that added mass doesn't help. It just slows down the response time of the system.


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## Woodrat (Feb 10, 2009)

precaud said:
			
		

> It just slows down the response time of the system.


----- If by "response time" you mean the amount of time before I get meaningful heat from the stove-- The Nashua is so big and I'm moving so much air (about 600 CFM) through its internal passages- inside of 10 minutes in the AM, I'm getting 3/400 degree air coming out of the side vents of the stove-- I'm a happy camper! Additional benefit to the high volume of high temp air is that I can dry my freshly cut/split firewood in a matter of days. Has taken many years to get it down to a "science", but it works very well!

Best wishes,  Woodrat


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## precaud (Feb 10, 2009)

No, that's not what I mean, but that's ok. Enjoy your setup - it works.


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## precaud (Feb 11, 2009)

Yesterday I did another round of three burns, using rounds instead of splits.

Zircar refractory liners
Load 1 :  620 Top...440 Side
Load 2 :  700 Top...500 Side
Load 3 :  720 Top...500 Side

As one would expect the rounds don't burn as fast so temps were down a bit. But the temp on the sides remained higher. Smoke output was quite a bit higher. The first two loads didn't burn all the way to the back. And the coals buildup came back, as rounds don't burn off as fast. So while the refractory liners do make a big difference, it doesn't solve all the problems of this stove. No surprises there.

Think twice before buying a stove with cast iron liners.

This experiment is closed for now. The X33 is reinstalled. It's getting cold here again.


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## begreen (Feb 11, 2009)

The ceramic insulation is impressive. It gives some great results in this test. However,I can't completely agree with the final conclusion. Having owned the predecessor of that stove and a few other cast iron lined stoves, none had the issues reported with this 602CB. All exhibited very good, even burning and there were no coaling problems. They were all good heaters too. And smoke during the burn was not an issue. Quite the opposite, normally you wouldn't know the stove was burning by looking outside at the flue. Even the old 602 didn't smoke except on startup. In the newer EPA castiron stoves I've owned, the firebox definitely stayed hot enough and even enough to support great secondary combustion and even burning. 

I'm wondering if this could partially be related to high altitude burning? My neighbors have a 2 yr old 602CB (at low altitude). I'll try to stop by on the weekend and will ask how their stove is burning, especially regarding the back of the box.

However, that's not to say that a good stove can't be improved upon? I wonder if one can get hold of used space shuttle tiles?


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## precaud (Feb 11, 2009)

BG, you're reading me wrong. In no way am I suggesting that iron liners cause coaling. In fact, I said that burning rounds made it worse. Nor am I saying that stoves with cast iron liners are "bad." They're just lower in efficiency than they could be. And I am absolutely certain that the performance of ANY EPA stove with cast iron liners can be improved with refractory liners. If you disagree, set up an experiment that demonstrates it. Replace the nice ceramic bricks in your T6 with iron pieces and see what happens. You won't like it.

Look at the trends in the high efficiency heaters using other fuels. Low-mass, super-insulated combustion zones, followed by low-mass heat exchangers.

"Over the last 50 years many new _high temperature insulation systems and materials_ have been developed and have provided significant benefits to the process industries... The economic benefits of _low thermal mass systems_, through energy saving in intermittent/cyclic temperature processing and _lightweight constructions_ is now well documented. These factors have enabled industry in N America and Europe to make savings currently estimated at US$2.5B/annum, and to reduce emissions of greenhouse gases by-15M tonnes/annum." (WIPO)

The same principles hold true for woodstoves. You do not get "super-insulation" with cast iron liners, because iron is not an insulator. And it weighs too much. The only reason I see for choosing cast iron liners is if you own a foundry and are trying to make use of it. It's not state-of-the-art design engineering.

It's unlikely that high altitude had any effect on this test. The stack is a 25 ft rigid stainless liner in a central masonrychimney. Draft is excellent.

Look at the back of your friend's F602, I am certain it will be black. How can it be otherwise? There is no air back there.

Maybe someone with a different stove with cast iron liners will step up and replace them as I've suggested and report the results. Until disproved, I stand by my conclusions.


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## Peter B. (Feb 11, 2009)

precaud:

I've read much of this thread at least once, but may have missed some relevant points, and have some questions for you.

Somewhile ago, I lined the lower firebox of my old cylinder stove with dense heavy firebrick (halves or 'splits').  The intent (or hope) was to protect the cast firebox from what I anticipated might be a routinely hotter fire (and possible coal burning).  I also thought the bricks would help retain heat within the (brick) surround to help elevate firebox temperatures.  I suspected I was trading off some of the direct radiating capability of the firebox, but figured the other (believed) benefits were worth it.

I'm now in doubt whether I achieved either goal (even in part) by the use of the dense brick.

Would you care to speculate on same?  Do you think I'd be better off using lightweight brick instead?  Does it stand up to routine mechanical shock as well as the dense brick?  Is it very costly?

At this point, I'm torn between removing the brick altogether (to regain firebox volume), replacing the broken dense bricks next year, or replacing the dense brick altogether with the lightweight variety.

I'd be curious to hear your comments.

Thanks.

Peter B.

-----


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## precaud (Feb 11, 2009)

Hey Peter,
First, it's not clear to me if better insulation is a good thing for such a stove. That's why I've said it would improve any EPA stove. Without an above-fire secondary air system, it may just make things worse.

I'm remembering the year or two back in the 80's when I had Godin stoves, ornate sheet-metal cylinders lined with dense clay firebrick. I burned wood in the shoulder seasons and coal in the winter. Good little coal stove but really bad for wood - burned very dirty.


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## karri0n (Feb 11, 2009)

Peter, since you have the secondary mod, and based on where you put your baffle and secondary air inlet, I'd be willing to put my money on the lightweight insulating firebrick vs. the hard clay you have now. I'd imagine the hard clay is indeed helping, but holding as much heat in to help with your secondary as possible seems like the best move in your case. This helps the EPA stoves by increasing firebox temps, but since yours is self engineered, I would imagine that it might not hold as high a firebox temp as an EPA stove.(not bashing your design, in fact I love it) Knowing this, I would imagine the lightweight firebrick which has now been proven effective at holding higher temps within the firebox would greatly improve your combustion and efficiency. As far as  know, the prices are pretty comparable between the two types. According to firebricks.com, there are quite a large number of low density and high density types to choose from, and I would imagine one with a good balance of insulating value and price is the best for your application.


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## EddyKilowatt (Feb 11, 2009)

precaud said:
			
		

> Cast iron : 150+ (from 55 at 200Fº)
> Firebrick (heavy, yellow) : 14 (5.5 for a typical 2.5" thick brick)
> Firebrick (light, insulating) : 1.1 (0.88 for a typical 1.25" thick brick)
> Skamol V-1100 Vermiculite slab : 1.10 (slabs are typically 1" thick)



Precaud, mind if I ask your source for this data?  I'm curious to see the units and testing methodology, so I can compare these solid refractories with the fiber blanket I'm using.

I'm not here to mount some great defense of cast iron, but I will again point out that I'm burning a stove with cast iron firebox liners backed with refractory fiber insulation, and it is no effort at all to get both the firebox and glass up to self-cleaning (i.e. hot) temperature on every burn... with a flue that stays clean and no visible smoke out the top.

I have to doubt that you'd find any EPA stove these days with cast iron firebox liners that didn't have some kind of supplemental insulation behind the liners.  The overall goal, as you point out, is to reduce heat flow out of the firebox in order to maintain high combustion temperatures... while meeting various secondary goals like ruggedness, durability, structural design, and cost.  There are several ways to meet those goals, and advanced refractory materials are one of them... but iron with supplemental insulation is certainly another (especially for manufacturers already tooled for iron).   I think you'd need a pretty sharp pencil and a lot of data to conclusively prove that one approach beats the other in the wood stove firebox.  (And note that the answer may well be very different for the industrial furnace, which has a different set of requirements.)

Eddy


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## precaud (Feb 11, 2009)

EddyKilowatt said:
			
		

> Precaud, mind if I ask your source for this data?  I'm curious to see the units and testing methodology, so I can compare these solid refractories with the fiber blanket I'm using.


Hey Eddy, I'm at work now, I don't have that info. I'll have to do some backtracking to find the sources I found.
All by itself, the fiber blanket is superior to more dense ceramics, but obviously that changes when compressed between two pieces of iron.



> I'm not here to mount some great defense of cast iron, but I will again point out that I'm burning a stove with cast iron firebox liners backed with refractory fiber insulation, and it is no effort at all to get both the firebox and glass up to self-cleaning (i.e. hot) temperature on every burn... with a flue that stays clean and no visible smoke out the top.


I don't doubt that. But it would be even better with ceramics.



> I have to doubt that you'd find any EPA stove these days with cast iron firebox liners that didn't have some kind of supplemental insulation behind the liners.


Agreed. And they all would benefit from what I've suggested.



> The overall goal, as you point out, is to reduce heat flow out of the firebox in order to maintain high combustion temperatures... while meeting various secondary goals like ruggedness, durability, structural design, and cost.  There are several ways to meet those goals, and advanced refractory materials are one of them... but iron with supplemental insulation is certainly another (especially for manufacturers already tooled for iron).   I think you'd need a pretty sharp pencil and a lot of data to conclusively prove that one approach beats the other in the wood stove firebox.  (And note that the answer may well be very different for the industrial furnace, which has a different set of requirements.)Eddy



Sounds to me like you're the guy we've been waiting for. Replace your cast liners with equal size ceramic and test your conviction. I'll bet against the iron/ceramic wool sandwich any day.


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## karri0n (Feb 11, 2009)

I agree that if you left the ceramic wool in there and replaced the iron with fiberboard you would probably at least slightly raise temps inside the firebox, but you would certainly be sacrificing durability in a system that is already tested working using the current configuration. I've been known to occasionally be a bit rough with loading, and with nothing rigid behind the fiberboard, I would be really scared of damaging it.


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## Peter B. (Feb 11, 2009)

precaud:

As karri0n mentioned, I do in fact have a rudimentary secondary air supply that feeds the fire near the coal bed... and the coal bed / lower firebox is the area where I want the highest possible temps to prevail.

So again I might ask whether you think the lightweight firebrick surround would do a better job of maintaining elevated temperatures... at the same time being as durable - mechanical shock (i.e. repeated loading) wise?

I tend to think of the lightweight brick as being fragile... maybe I'm plain wrong.  I don't know offhand how to make a ready comparison of the physical characteristics of the two bricks.

Thanks.

Peter B.

-----


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## precaud (Feb 11, 2009)

Peter,
I didn't know about your added 2ndary. Sounds like a fun project.

Yes, there is no question the lightweight firebricks will keep temps higher. As to durability, my Quad has them and I've not broken one in 2+ seasons of use. Perhaps you will have to be a hair more careful, and not do things like slam tools into them and such. I assume you keep some ash on top of them, which protects them some.

The difference between the twp types of bricks: One resists heat, the other absorbs and stores it. You want a firebox that is lightweight and highly insulated, not one that stores heat.

The F602 that I modded also has a massive cast iron piece with ceramic wool underneath that the fire is built on. I make take another step and replace that with IFB (Insulating FireBrick). karri0n is right, IFB is the same price as the heavy stuff in standard sizes. I haven't found a good source for the half-thick IFBs yet, have you?


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## begreen (Feb 11, 2009)

precaud said:
			
		

> BG, you're reading me wrong. In no way am I suggesting that iron liners cause coaling. In fact, I said that burning rounds made it worse. Nor am I saying that stoves with cast iron liners are "bad."
> 
> Maybe someone with a different stove with cast iron liners will step up and replace them as I've suggested and report the results. Until disproved, I stand by my conclusions.



Maybe I misstated the case. The results are good. I don't disagree with the findings, but do take  exception the statement to "think twice before buying stoves with cast iron liners". That's like saying don't buy a Chevy Cobalt because it can be improved as a hybrid. Sure this mod can be added (at great expense) but that doesn't make the Cobalt a bad car. At 37mpg it still a nice vehicle, right?  There are other factors in buying a stove besides ultimate efficiency. I have no problem recommending the Jotuls, Isle Royale or Hearthstone cast iron stoves, regardless of liners. Actually with a top loader I'd prefer the toughest, most durable liner I could get.


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## karri0n (Feb 11, 2009)

My Isle Royale is equipped with the low density firebrick, not cast iron liners. On the sides of the firebox near the front, there is a sheet of cast iron, but behind it is still the low density firebrick.


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## precaud (Feb 11, 2009)

BeGreen said:
			
		

> Maybe I misstated the case. The results are good. I don't disagree with the findings, but do take  exception the statement to "think twice before buying stoves with cast iron liners".


That's my opinion. You have different priorities.



> Sure this mod can be added (at great expense) but that doesn't make the Cobalt a bad car...  There are other factors in buying a stove besides ultimate efficiency. I have no problem recommending the Jotuls, Isle Royale or Hearthstone cast iron stoves, regardless of liners. Actually with a top loader I'd prefer the toughest, most durable liner I could get.


Gawd guys, the pessimism and inability to keep things in context is amazing.

I AM NOT SAYING WHAT I AM NOT SAYING! Sheesh. If you love cast liners, knock yourself out. Start a thread extolling their virtues. Recommend whatever stove and brand and design you want to. There are hundreds, maybe thousands of threads on this website doing just that - do you want to turn this thread into another one of those? Gimme a break. That has nothing at all to do with this experiment and further ones to come in this direction. And they will follow - this is just the start, folks. Now's the time to do it, before wood heating season goes away. And in spite of the negativity I encounter here, some from completely unexpected sources, I will continue to post the details.

About the expense: I have never recommended that anyone go out and buy RS-1200 for their stove. In fact, I said don't do it, it's not cost effective. This is just stage one of this process, done to one stove. Going out and finding lower cost materials is a totally separate job from making a hypothesis, setting up an experiment, and testing it. Lower cost, and maybe even superior, alternatives will be found. Some of them already exist.

Maybe you're not, but I AM learning alot from this. It's given me insights and shattered some myths.


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## begreen (Feb 12, 2009)

Precaud, this is not negativity, more practicality. Most folks buy and use -one- stove for their heating needs for many years. They are not experimental in nature. After the large expense of the stove the last thing they want to deal with is tweaking their stove towards it's ultimate efficiency. Don't get me wrong, I love your tests and experiments. Please don't stop! This is good information. But in the big picture, folks buying stoves have to deal with what is available, tested and warranted with currently available stoves. 

You are doing good research. If anything,  your results should be communicated towards the stove companies making these stoves. No doubt, there's always room for improvement. Yes there is room for improvement. Case in point, how many stove employ what your testing shows so far? What stoves are out there employing high grade ceramics for liners?

My point is that if this dialog is still from a purchasing standpoint hypothetical, then it doesn't seem fair to make owners of current technology stoves feel like they have purchased their stoves in error.


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## karri0n (Feb 12, 2009)

Precaud,


Please don't take offense at BG's post. He's going for discussion, not conflict. I'm quite certain BG is not attempting to dispute your findings or the relevance of them. It seems to me he's providing reassurance to those who may have stoves with cast iron liners that might see your findings and think that they have purchased the wrong stove. Frankly, I'm quite impressed with your findings and would be quite interested in your next update.


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## kksalm (Feb 12, 2009)

This is a fascinating subject. One of my first inquires to this forum was questioning the logic of placing a more efficient wood stove inside my mammoth Hearthstone I. The needed replacement parts (cast iron) are either no longer available or the cost is astronomical. After following the thread on adding secondary combustion and now this thread in particular I can actually rebuild my stove cheaper and have a more efficient product as well. Bt all means, please continue with the experiments and continue to post your thoughts. It is much appreciated.
Best regards, kksalm


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## begreen (Feb 12, 2009)

Yep, I do love this kind of research and hope to see more interesting data. 

Ken brings up one thing that I was wondering about. Would the greater heat transference of the Zircar help in the case of an old soapstone stove or would it risk cracking the stones due to the higher temp.


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## Dexter (Feb 12, 2009)

For what it's worth, I changed the iron top burn-plate(s) of my Jotul Firelight cb with home-cut white/grey split firebrick.  I've only done heating curves with the brick.  'Never did it with the Iron.  Anectdotally, however, my typical fires with the original top plates seemed to top-out at about 600 f. with the thermometer on the top right rear of the stove.  Now it's hard to get it over 525, and it takes a long time to get it higher than that.  Curiously, the heating of the house is perhaps better:  'Lots of radiant heat out the front, sides and back, and extremely clean glass for many weeks.  (Burning 24-7 during winter would warp the iron over 2 or 3 seasons.)

Best Regards


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## johnn (Feb 12, 2009)

"precaud"  Been A nice thread with a good learning curve for myself, thanks to you and all those sharing.I`ve followed this from the beginning, and intended on tinkering with my old steel box,,still thinking? Considering input from this thread and realizing the construction of my burner, Ive developed many questions as to the probability of success,,,most of these issues I feel would not be considered favorable to the content of discussion, and will try to find answers through the "navigation history"

 However in your earlier thread you had two objectives: ALTERNATIVE MATERIALS and MODIFICATION.
What thoughts might you entertain on how to modify, the thinner "Fire Brick" (space and economics may leave many in this scenario)?


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## johnn (Feb 12, 2009)

OH yes, I forgot to mention how much I envy your SUNSETS and SUNRISES111


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## precaud (Feb 13, 2009)

Thanks for the support, guys.


> It seems to me he’s providing reassurance to those who may have stoves with cast iron liners that might see your findings and think that they have purchased the wrong stove.


karri0n, apparently it's a moderator's job to protect the feelings of those folks. Seems like nonsense to me. I don't think such a user will ever even read a thread like this. If they're so upset, perhaps Hearth.com can start a new forum/support group for them. Iron Liners Anonymous, maybe. 

kksalm, keep us posted on what you do and how it turns out.

Dexter, I'm not familiar with the Firelight. Is this a liner under the top plate? Or is it the baffle? Can you post a pic of this?



> What thoughts might you entertain on how to modify, the thinner “Fire Brick” (space and economics may leave many in this scenario)?



ml, what's their thickness? The ones used in most modern stoves are 1.25" thick, called "splits' in the industry. I only looked briefly, and don't know of a good source for them yet. Am hoping someone will discover and post one. There's a guy on eBay selling some but they're the old heavy type.

And yes, the sunrises/sunsets are wonderful...


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## Dexter (Feb 13, 2009)

PreCaud:

Re: your last.  Mine is an early version of what is now the 600 cb.  I use 1.25 split firebrick (whitish/grey).  It is held over the secondary burn tubes 3/16" using cold-rolled steel dowls.  I used a hand-held dremmel-type cutting tool and a borrowed diamond blade to cut them into an approximately 14 3/4" square of bricks.  I still use the insulating blanket over the top of them.  'Third season burning this way.  'Seems to work well.  Chimney cleaning is about the same.  Got firebricks at a hardware store in Boulder.  Their motto is:  "If we don't have it, you don't need it."

Regards,

Dexter


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## karri0n (Feb 13, 2009)

Precaud, The only source I've managed to find is firebricks.com, and it seems they only supply to furnace manufacturers and the like. What was the source that you used for the pieces that you fabricated?


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## kksalm (Feb 13, 2009)

I usually check here first
http://shop.ebay.com/?_from=R40&_trksid=m38&_nkw=ceramic+firebrick&_sacat=See-All-Categories
Cheers, kksalm


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## precaud (Feb 14, 2009)

Glad to hear it's working well, Dexter. The store in Boulder, does it happen to be McGucken Hardware?

karri0n, I've looked at firebricks.com before but the problem is the very sketchy info they provide about each item. No K factor at any temperature, no compressive strength, nothing about color, no hardness, and most have no density spec. Some of these are needed to see if it will stand up to use in a woodstove environment. It would be a crap shoot ordering from them.


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## begreen (Feb 14, 2009)

precaud, what have you found as the closest second to the Zircar material? Would zirconia bricks be similar?

http://www.zircoa.com/assets.common/pdfs/insulating.structures.pdf

also found this company offering various refractory brick compositions
http://www.mcgillswarehouse.com/Itemslist.aspx?GroupID=12211&GN=INSULATINGBRICKS

I'm also wondering about refractory bricks for glass kilns and the like. They come in standardized sized similar to wood stove sizes, but no idea about their durability.


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## kenny chaos (Feb 14, 2009)

If we're brain storming here then any silly idea is okay to throw on the table?
How about making some good old fashion vermiculite panels?


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## precaud (Feb 15, 2009)

Give it a try. I bought some but haven't used them. My thinking says anything in the flame path is better if it's white. Or at least starts out that way 

I pulled out the bottom liner of the F602 today, two cast iron pieces weighing 8 lbs each, with a 1/4" sheet of ceramic wool underneath. The dimensions of the stove floor are 9-1/8" x 16-1/4". Standard 9" IFB's will fit nicely down there and should hold up fine on the floor - this will raise interior temps another notch. I'll be looking around the 'net to find some this weekend. Something in the 1-1/4" to 2" thick range.

Added: Vermiculite does have some nice properties for use in a wood stove:
http://www.opie-woodstoves.co.uk/skamol.htm

My Nestor Martin has Skamol panels on the sides and had a Skamol baffle too. I replaced the baffle with Kaowool M Board, resulting in the firebox heats up much quicker, and the 2ndary burn is hotter and more intense. I'm tempted to replace the side panels too.

"Vermiculite is the geological name given to a group of hydrated laminar minerals, which are aluminium-iron magnesium silicates."

My experience is that it is not as insulative as it's decent K values suggest. Certainly better than an iron/ceramic sandwich but not as good as the ceramics.


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## precaud (Feb 15, 2009)

BeGreen said:
			
		

> precaud, what have you found as the closest second to the Zircar material? Would zirconia bricks be similar?
> http://www.zircoa.com/assets.common/pdfs/insulating.structures.pdf



Corrected: Zircoa is a different company than Zircar. They appear to be using the same Zirconium-based materials as the basis for their sheet, brick, and custom-shaped products. I talked at length with one of the Zircar apps people, he agreed RS-1200 was overkill pricewise for a wood stove, but might be the only thing they had rugged enough to hold up to abuse. He said their ZIRCAL-95 material has similar properties at half the price of RS-1200 but has less abrasion resistance so I think we'd have to check it out before recommending it. But at $32 per sq ft., even that stuff is pricey.



> also found this company offering various refractory brick compositions
> http://www.mcgillswarehouse.com/Itemslist.aspx?GroupID=12211&GN=INSULATINGBRICKS



Yes, I saw their stuff and wrote to them, the prices are good but no real specs. They have nothing in 1-1/4" thickness.



> I'm also wondering about refractory bricks for glass kilns and the like. They come in standardized sized similar to wood stove sizes, but no idea about their durability.


You're on the right track, as that's the main appplication area for all of these materials, and the durability vs. low K factor is the issue for us. That's exactly what I'm looking into. And also some possible surface treatments to make the bricks more durable. like ITC 100 HT and ITC 296:
http://www.axner.com/axner/equipment/itc-ceramic-coatings.php
Again, pricey stuff...


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## begreen (Feb 15, 2009)

Were you able to locate a retailer for zircoa bricks -  9 x 4.5 x 1.25"? If so, do you know what are they running per brick?


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## precaud (Feb 15, 2009)

The apps guy said McMaster-Carr sells their stuff. But I look on their site and they don't identify the manufacturer, so we don't know who makes what. MC doesn't sell any 1.25" brick... only 2.5".

This co. has some 3/4" brick that looks interesting, halfway down the page:
http://www.zoellerforge.com/flare.html

And this 2" thick stuff looks promising:
http://cgi.ebay.com/Firebrick-kiln-ceramic-oven-15-pr-bx-Morgan-K-28-silica_W0QQitemZ290263097610


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## jebatty (Feb 15, 2009)

Finished reading the entire thread and very interesting. My old SeeFire (bot 1990) has a fully lined firebox with, I assume, the dense yellow firebrick. It is, except for backup heat when we're gone, our only heat source - 19 heating seasons now. I replaced about 1/2 of the firebrick 8 years ago due to deterioration. We live in a very cold area (saw -36F twice this winter), windy, etc. We burn 4-5 cords of aspen each heating season. 

I didn't notice cost info on the various materials, except the RS-1200 at $63 sq ft. That's about the cost, if I bought it, of 1 full cord of aspen where I live. 

What is the bank for the buck of the various materials? What is the gain in btuh output from the increase in efficiency? What is the durability relating to pushing/throwing in fresh logs which hit the back of the firebox? What is the longevity of each material and payback as to useful life under normal home stove usage and increased btuh output? How easily is each type of material formed, cut or broken to fit a stove (the firebrick lay right in my stove as the firebox is designed to hold full bricks)? 

Although the fire in the firebox may be hotter with some materials, unless the stove is designed for that material, will the extra heat be usable? ...will it just go up the chimney because it no longer can be radiated through the sides and can only radiate from the top and the flue? Is it possible that the air intake design for a particular stove (with dense yellow firebrick, for example) produces a very efficient burn with good heat radiation, and that burn no longer will be correct for a different "firebrick" lining?

I am reaching the point when more firebrick will need to be replaced in my stove and some real world economics and performance would be useful in deciding which material to use. Thanks.


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## precaud (Feb 15, 2009)

jebatty, I just wrote a thorough response and apparently didn't click on submit... so here we go again.
You ask good questions. Some of them cannot be answered by me, as I only have so much time and resources to give to this experiment.
Some will find answers as the process unfolds, and as other users experiment with their stoves and post the results.
It's unlikely that hard figures of btu increases or efficiency percentage gains will come out of this experiment.
Workability: Most refractories can be cut using normal woodworking tools. Some may require special masonry blades.


> Although the fire in the firebox may be hotter with some materials, unless the stove is designed for that material, will the extra heat be usable? ...will it just go up the chimney because it no longer can be radiated through the sides and can only radiate from the top and the flue?


Huh? Perhaps you should read again... the only experiment thus far resulted in higher temps inside and out.


> Is it possible that the air intake design for a particular stove (with dense yellow firebrick, for example) produces a very efficient burn with good heat radiation, and that burn no longer will be correct for a different “firebrick” lining?


Unlikely. A good air system design will be able to take advantage of a better environment for combustion to occur. But a change in lining material will not correct for a bad air design. The F602 is a good example of this.


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## precaud (Feb 15, 2009)

duplicate post, sorry


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## precaud (Feb 15, 2009)

Here's a photo of the original F602 cast iron liners for the bottom of the firebox, weight 16 lbs, alongside one I just made from 1" vermiculite slab, weight 4.5 lbs. The vermiculite cuts like butter on a tablesaw.

The side runners were necessary to get the Zircar side panels at the proper height. Jotul had 1/4" ceramic wool under the iron liners, so I'll leave that in place under the vermiculite and reinstall the stove tonight for burn tests tomorrow and Tuesday. Fortunately I cut the stovepipes so that it only takes about a half hour or so to swap the stoves...


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## kenny chaos (Feb 15, 2009)

I saw this and pictured precaud piecing together high tech insulation to blanket the globe, hence, global warming.
http://photoblog.msnbc.msn.com/archive/2009/02/12/1792539.aspx?GT1=43001


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## begreen (Feb 15, 2009)

Note, this is for an F602CB and not for the original F602. The bottom liner (one piece) is different on the F602.


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## 68 Couper (Feb 16, 2009)

Today I was at TSC in the area and they had a pallet of fire bricks for sale at 2.50 each on clearance. They had a light orange color and were not as heavy as the bricks at Menards. Could these be the better variety?

Thanks,
Couper


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## precaud (Feb 16, 2009)

BeGreen said:
			
		

> Note, this is for an F602CB and not for the original F602. The bottom liner (one piece) is different on the F602.



Huh? I've never heard of an F602 that was not a CB.


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## precaud (Feb 16, 2009)

68 Couper said:
			
		

> Today I was at TSC in the area and they had a pallet of fire bricks for sale at 2.50 each on clearance. They had a light orange color and were not as heavy as the bricks at Menards. Could these be the better variety?


Lighter weight is a good thing. Ask them for more data. For lining the side walls I'd want something with less color, i.e. as close to white as possible.


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## begreen (Feb 16, 2009)

precaud said:
			
		

> BeGreen said:
> 
> 
> 
> ...



The 602 had a long life before they added the secondary air assembly for EPA qualification and the CB designation. IIRC it first showed up in the 1940s. We have the pre-EPA version. Great little stove. It has a record of being one of the most popular stoves sold. Here's a picture of the 602 in the back row. It's the red model, one from the right, next to the green unit on the right. Our's is the identical unit, same color and even has the same trivet top. There's a black one in the upper back corner too.
https://www.hearth.com/visit/woodsmans/source/1505jotuls.html


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## precaud (Feb 16, 2009)

That's 602, not an F602. You and I have extolled the virtues of the old 602 many times on this site.


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## begreen (Feb 16, 2009)

My bad, the numbers got blurred in my fuzzy mind. I just looked at the old parts diagram that I 'thought' had it listed as an F602 and no, it's a simple Nr. 602.


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## precaud (Feb 16, 2009)

Does your 602 diagram show an internal bottom liner? I don't remember mine having one.


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## begreen (Feb 16, 2009)

There is an iron bottom liner and insulation of some sort underneath. I'll scan the copy and will post it in the Jotul stove wiki area.


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## karri0n (Feb 16, 2009)

Still very interesting. I badly need to replace several bricks n my IR, and I plan on researching further and following this thread so we can find a good brick with a decent performance:rice ratio.


@Precaud: as to the sketchiness of firebricks.com, I think you are supposed to go there already knowing what you're looking for. The site seems to be for manufacturers.


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## Peter B. (Feb 16, 2009)

I'm also interested in finding insulated firebrick splits... (9" x 4" x 1.25" or 1.0") but don't feel myself knowledgeable enough to evaluate their properties... even if I were to find a source myself.  (I'm also on a dialup connection which makes 'dedicated' web searching an agonizingly slow process.)

So, I'm hoping precaud will 'spill' if/when he finds a source...

Please and Thank You.

Peter B.

-----


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## precaud (Feb 17, 2009)

Today I did the usual round of three burns, with the Zircar side liners plus the vermiculite bottom in place. Results:

Load 1 :  680 Top...500 Side
Load 2 :  820 Top...520 Side
Load 3 :  780 Top...570 Side

Compare this to the original set with standard cast iron liners:
Load 1 :  550 Top...370 Side
Load 2 :  670 Top...430 Side
Load 3 :  730 Top...450 Side

VERY fast warmup, and almost a 100F average increase in output temps on the top and sides with the same size fuel load and same air settings. Not bad. I've never felt this stove radiate like it now does. It's now in the same league as our fave the old 602. The clean burn pattern on the side liners extends even farther back into the stove and is almost completely free of residuals. Smoke out of the chimney was the cleanest I've seen out of this thing. The 2ndary flames on the second and third loads were like nothing I've ever seen on this thing. (Too bad you have to lay on the floor to see it...)   All three loads left no unburned wood in the back - the raised internal temps appear to be enough to gassify the whole load now. This stove is now performing as I thought it would when I bought it, and is no longer an underperformer.

All this from better insulating the firebox and taking 21+ lbs of mass out of the lining. I hope this demonstrates clearly that the whole concept of using mass to "hold the heat" inside a firebox is a bad idea. To hold it, you must take it from where it's really needed. Low mass and high insulation is where it's at.

I think that's about as far as I can go with the F602 stove, except maybe adding some leakage air at the bottom rear and a few air holes at the very back of the secondary manifold. I wish I had something that uses standard firebrick splits to play with. (The Quad does, but it's lining is already excellent.) I'll continue to look for 1.25" IFB's but someone else will have to try them out. Meanwhile, I'm keeping an eye out for 1" ceramic material to replace the Skamol on the sides of the Nestor Martin.


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## Jimbob (Feb 17, 2009)

Very interesting. It seems to support the argument that the light firebrick would work better than the heavy, dense stuff. I't not exactly what you were testing but sort of along the same lines.


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## begreen (Feb 17, 2009)

Good data and nice results. To summarize so far:

_Zircar refractory liners only_
Load 1 :  650 Top...440 Side
Load 2 :  750 Top...500 Side
Load 3 :  770 Top...510 Side

_Zircar liners and vermiculite bottom liners_
Load 1 :  680 Top...500 Side
Load 2 :  820 Top...520 Side
Load 3 :  780 Top...570 Side

_Original set of standard cast iron liners_
Load 1 :  550 Top...370 Side
Load 2 :  670 Top...430 Side
Load 3 :  730 Top...450 Side

How would you rate the durability of the vermiculite bottom liners? Weak, moderate, strong? For cost reduction have you considered casting with any of the refractory mixes that the VC owners have been experimenting with to cast their own combustion boxes? It would be pretty easy to make your own forms for standard brick sizes.


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## precaud (Feb 17, 2009)

Jimbob said:
			
		

> Very interesting. It seems to support the argument that the light firebrick would work better than the heavy, dense stuff. I't not exactly what you were testing but sort of along the same lines.


Jimbob, it does very much support that argument. The iron/ceramic wool sandwich is likely the worst case, but the heavy colored firebrick would be next to it at the bottom of the list.


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## precaud (Feb 17, 2009)

BeGreen said:
			
		

> How would you rate the durability of the vermiculite bottom liners? Weak, moderate, strong?


It appears to harden to a more brick-like consistency after being fired a few times. Based on the Skamolex in the Nestor Martin, used on the sides and bottom, I'd say it's very strong. (The slabs I used are from Skamol.)



> For cost reduction have you considered casting with any of the refractory mixes that the VC owners have been experimenting with to cast their own combustion boxes? It would be pretty easy to make your own forms for standard brick sizes.


For unusual shapes/sizes, it might be a good idea, I'd have to look into the material properties. It's so much easier to work with readily available material of the right thickness, if it can be found...

It also would have been nice to have a few more sensors, capture the output with a data logger at regular intervals, and plot the sequence of burns so one can better see the area under the curve. I have the logger but not the thermocouples...


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## kenny chaos (Feb 17, 2009)

It would be interesting to know the fluctuations in the flue temps during each firing cycle.  Those can be very telling.
It'd also be interesting to know the variations in burn times.  Maybe by reducing mass, you will be reducing time of total burn (soapstone affect).
It sounds like you're convinced of your resluts and I applaud your time, effort, and sharing, on this project.


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## karri0n (Feb 17, 2009)

Precaud, what is the difference in the R value of the vermiculite and the zircar liners? I'm wondering if vermiculite might be a possible low cost alternative to the zircar for  the lining.


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## jebatty (Feb 17, 2009)

The vermiculite slab, since it cuts so easily, would it make sense to install it behind the firebrick lining? Would reduce the size of the firebox but would add the heat resistance value.


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## precaud (Feb 18, 2009)

karri0n said:
			
		

> Precaud, what is the difference in the R value of the vermiculite and the zircar liners?


The thermal coefficient (Tc) of these materials (K) at 1000º are (lower numbers are better insulators):
Skamol V-1100 Vermiculite slab : 1.10
Zircar RS-1200 : 0.66

These numbers are per inch of thickness, so you multiply it by (1/thickness in inches). So 1/2" RS-1200 is 0.66 x 2 = 1.32, and 1" vermiculite is 1.10 ( I have never seen any Skamolex other than 1" thick).

This Tc rates the material's _convective_ (i.e. air-coupled) resistance to heat transmission. The basic test has two chambers at equal temperature with a piece of the material being tested in between. One chamber's temp is raised by X amount, and the time it takes for the other chamber to rise by Y degrees is measured. That's basically how the Tc is calculated.

Compared to a woodstove firebox, what is missing from this test? Radiant heat. The heat source is outside the chambers and piped in. A large amount of the heat in a firebox is radiant, from the flames and the hot coals. The darker the color of the liner, the more it will absorb the radiant heat. It is no accident that the best insulators are white or nearly so. And that requirement dictates the materials that can be used to make it. Materials that are either white or colorless and can withstand high temps are expensive.



> I'm wondering if vermiculite might be a possible low cost alternative to the zircar for  the lining.


Sure, especially on the bottom, where it's color would be buried in ash so it won't absorb the radiant heat. For the sidewalls, it's not as good as a good lightweight firebrick.

But it's important to say again... which material you choose is going to be largely dictated by the thickness of the liner you're replacing.


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## precaud (Feb 18, 2009)

jebatty said:
			
		

> The vermiculite slab, since it cuts so easily, would it make sense to install it behind the firebrick lining? Would reduce the size of the firebox but would add the heat resistance value.


See previous post. Sure, it adds insulation, but it adds weight too. You want high insulation AND low mass.


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## precaud (Feb 22, 2009)

These guys sell vermiculite slab in 1" and 1.5" thickness:
http://www.euclids.com/kilnbuild&repair;.htm

I'm still looking for a good source for IFB splits in the 60-70 lb. density range. All the 1.25" bricks I've found so far are not the insulating type.

There is a seller on eBay that has 2800º 65 lb. density IFB in 2" and 2.5" thicknesses, made by Thermal Ceramics, 30 bucks for a box of 15, and has lots of it available. That's a super price, but you'd have to cut it down to the desired thickness with a tablesaw or handsaw. I got the spec sheet on the stuff, and it's better material than any stove mfr is putting in their stoves right now, and would hold up as well as or better than the stuff PE and Quad are using.
http://cgi.ebay.com/Firebrick-kiln-ceramic-oven-15-pr-bx-Morgan-K-28-silica_W0QQitemZ290263097610


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## kenny chaos (Feb 22, 2009)

Being a typical guy, I also waste too much time trying to invent a better mouse trap but it is fun to tinker.


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## precaud (Feb 22, 2009)

whadya mean, "also" ? Speak for yourself.


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## precaud (Feb 23, 2009)

Here are a couple interesting articles with tests of insulation materials for wood cook stoves, which are commonly used in poor countries around the world.
http://www.hedon.info/InsulativeCeramicsForImprovedCookingStoves
http://www.repp.org/discussiongroups/resources/stoves/Andreatta/Heatloss.htm

Though his numbers for thermal conductivity are lower than others I've seen for the same materials, his vermiculite and pumice brick formulations performed quite well in these tests. Pumice brick, which many believe is used in PE and Quad stoves, has very high insulation properties, on a level with K23 insulating firebrick. Density is around 50 lbs/cu ft., about the same as K23 bricks. I haven't found any specs on crush strength (an indicator of ruggedness) but it must be higher than the K23 which are quite soft and crumbly. Home Depot sells pumice brick pavers in several sizes if anyone wants to experiment with them. Masonry blades for a table saw are just a few bucks, and would probably be best for slicing them down to desired thickness.

Also interesting is their finding of the superiority of the low mass/high insulation firebox combination for clean combustion AND highest heat transfer.


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## karri0n (Feb 23, 2009)

How does castable refractory match up with the thermal properties of the other materials listed?


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## precaud (Feb 23, 2009)

Good question, I don't know the answer. Also there are many types of castable.


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## johnn (Mar 1, 2009)

Precaud: Your thoughts on K28, thermal ceramics,45%alumina,52%silicia, 1% ferric oxide. Better than K23`s??? MY mind keeps telling me whenever I read.,(...the brick used in kiln manufacturing...) that a kiln wants a brick which holds ,,rather than transfers heat,,. Does my mind have a mental block , 
or are these the type I want??
      Regarding the installation of a BAFFLE: Between the secondary tubes,baffle,1"insulation blankett, a lot of cu.ft gets consumed> Your thoughts on a free 1/2 in. stainless baffle coated with itc100 ceramic coating, to minimize cu.ft. reduction by not using the 1" insulation blanket. I think cost would equal out and leave more space. I`ve read all threads numerous times along with each added text and find myself still confused at times, not being able to understand the charts,,,I have been trying!!
   would cutting brick thickness down to 1" be acceptible?? IT seems that the "whitest " "or""( absense of color) in a brick are manufactured in either India or China. Not exclusive of course,,its just when I find a new link,,,its far away, and again I cant decifer the test charts. Thanks


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## precaud (Mar 1, 2009)

Hey ml, good questions.


			
				ml said:
			
		

> Precaud: Your thoughts on K28, thermal ceramics,45%alumina,52%silicia, 1% ferric oxide. Better than K23`s???


If you're referring to these:
http://cgi.ebay.com/Firebrick-kiln-ceramic-oven-15-pr-bx-Morgan-K-28-silica_W0QQitemZ290263097610

I have the specs on them. The 51 pcf density is pretty much equal to the pumice bricks. Crush strength is higher than the K23, so my guess is they are pretty much on a par with the pumice bricks in their handling of abrasion and bumps. They have better radiant reflection due to their whiter color. I may order a box of them this week. The price can't be beat.



> MY mind keeps telling me whenever I read.,(...the brick used in kiln manufacturing...) that a kiln wants a brick which holds ,,rather than transfers heat,,. Does my mind have a mental block, or are these the type I want??


Yes, they are the type you want. And yes, it's a mental block, caused by the use of the word "hold." Why do you want to hold heat in the lining? What for? You don't want to hold it, you want to stop it from escaping so that the interior space stays hotter. You have to separate in your mind:
1. the physical kiln from the space inside it. And for a woodstove,
2. Keeping the combustion environment hot from getting the heat out (the heat exchanger.)

If you try to do both in the same space you'll do neither very well.

Imagine this: you're in a one-room house with steel walls. You're putting heat into it, and you want to get the temps as high as possible inside the house. To achieve this, what treatment would you apply to the inside of the steel walls: line them with 2.5" of heavy brick, or spray 2.5" of lightweight foam insulation? The brick will store heat and even out the temperature fluctuations in the room. But that isn't the goal. The insulation will be MUCH better at stopping the loss of heat and making the inside temperatures higher.

You don't want _even_ heat over time inside the firebox; you want it as hot as possible while flames exist in it.



> Regarding the installation of a BAFFLE: Between the secondary tubes,baffle,1"insulation blankett, a lot of cu.ft gets consumed> Your thoughts on a free 1/2 in. stainless baffle coated with itc100 ceramic coating, to minimize cu.ft. reduction by not using the 1" insulation blanket. I think cost would equal out and leave more space.


Interesting idea. But how about a 1/2" ceramic fiber board? It weighs alot less than the stainless baffle and is a better insulator.



> would cutting brick thickness down to 1" be acceptible??


I'm thinking of the doing same thing, to replace 1" of vermiculite. As long as it's dense enough to hold up, I don't see why not.



> IT seems that the "whitest " "or""( absense of color) in a brick are manufactured in either India or China. Not exclusive of course,,its just when I find a new link,,,its far away, and again I cant decifer the test charts. Thanks


Yeah, the dust created is nasty stuff... inside-the-factory health regs are probably looser over there... make sure you wear a mask if you cut bricks down.


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## johnn (Mar 3, 2009)

Precaud: Thanks for your reply. In regards to the 1/2 in. ceramic board,,, would a coating still be worth trying to increase the temps near 2ndary reaction,,assuming the exhaust would create addequate stove top temps as it exits. That stuff really reflects heat, but life use is unknown. There is a much cheaper coating than the itc 100.
 Regarding cutting bricks: I remember years ago while cutting a concrete path with masonry blade,,,my step son shows up hollering about my not using a mask,,,claiming that the process of cutting was creating glass at the point of contact. I`ve worn masks since then, but would like to note: Reading the articles about poorer countries making brick,,and the natural fillers used which burn away at firing ect.ect...These pores playing a large roll in the design and function, it may be worth noting that a fibre cutting disk leaves the cut surface of a paver brick quite smooth, almost glossy. Just saying that,a diamond blade along with the use of water to combat heat and wear (those such as masons use) may be in order. I`d just hate to disrupt the pores by glazing them shut???


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## precaud (Mar 3, 2009)

ml said:
			
		

> Precaud: Thanks for your reply. In regards to the 1/2 in. ceramic board,,, would a coating still be worth trying to increase the temps near 2ndary reaction,,assuming the exhaust would create addequate stove top temps as it exits. That stuff really reflects heat, but life use is unknown. There is a much cheaper coating than the itc 100.


ml,  I haven't experimented with it, but I have my doubts about the effectiveness of coatings in a wood stove. It's not as if that stuff has magic insulative properties; best I can tell, it's a radiant barrier. But it's worth a try to see if it helps or not.



> Regarding cutting bricks: I remember years ago while cutting a concrete path with masonry blade,,,my step son shows up hollering about my not using a mask,,,claiming that the process of cutting was creating glass at the point of contact. I`ve worn masks since then, but would like to note: Reading the articles about poorer countries making brick,,and the natural fillers used which burn away at firing ect.ect...These pores playing a large roll in the design and function, it may be worth noting that a fibre cutting disk leaves the cut surface of a paver brick quite smooth, almost glossy. Just saying that,a diamond blade along with the use of water to combat heat and wear (those such as masons use) may be in order. I`d just hate to disrupt the pores by glazing them shut???


A smooth, glossy surface will be better, it's more reflective. The pores that matter are the ones inside, not on the surface.


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## precaud (Mar 28, 2009)

Since temps are on the rise around here, since the X33 needs a new door glass gasket (already...), and since a tendon tear is stopping me from doing more interesting things, last weekend I decided to put the modded F602 back in and live with it for a while. But before doing so, I decided to address the problem of no air (hence no combustion) in the back half of the stove. I drilled five holes in the secondary manifold in the very back of the stove, see the photo for locations. The yellow dots mark where the holes were drilled, 1/8" for the upper four and 7/32" for the bottom one.

The results are very good. As expected, there is now combustion in the back. No more unburned chunks to rake forward. The "clean burn zone" (the area that  burns clean on the side plates), extends another couple inches toward the rear. (One has to wonder why Jotul didn't put these holes there in the first place; every other EPA stove has 2ndary air back there. I'd bet it was a marketing decision - heaven forbid the little F602 outperform the F100...)

If I could do the holes over again, I'd do say six 1/16" holes above and one 3/16" below.

Everyone loved the pre-EPA 602 because it put out an amazing amount of heat from such a small box. The F602 came along with great fanfare but clearly underperformed its predecessor. But with these mods, this stove is now on a par with the old 602. It heats up as quickly, burns as hot, burns through each load reliably, and doesn't build up coals as quickly. So if you can pick up a used one for cheap (I've seen them for 300-350 around here,) it's probably worth doing these insulation and air mods and have yourself one nice little heater.


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## ernie (Apr 6, 2009)

Interesting, I have been thinking of replacing my firebrick in my Quad 7100 Fireplace with Skamol liners. What do you think about that? I think it might burn hotter and keep the glass cleaner.

Ernie


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## precaud (Apr 6, 2009)

> I think it might burn hotter and keep the glass cleaner.


More likely the opposite. 1" thick Skamol is a poorer insulator and weighs more than the 1.25" pumice bricks. That's not what you want. I think the only step up would be the K28 firebricks mentioned above. But you'd have to slice them in half to get the right thickness, easily done with a masonry blade on a table saw. But it's a dirty job. The dust is nasty stuff.

With the Quads, dirty glass isn't caused by low firebox temps, but by the design of the primary air system. The air feed is asymmetrical and weak at the edges. Despite that, they're one of the most efficient stoves out there.


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## precaud (Oct 15, 2009)

For the first time in decades, I am 602-less. Kinda weird.


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## johnn (Oct 17, 2009)

best of "Luck", precaud,,,dealing with your seperation anxiety :ahhh:


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## precaud (Oct 17, 2009)

sorry, double post


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## precaud (Oct 17, 2009)

Thanks ml, it didn't last long... within minutes after that post, I felt total relief!


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## BrotherBart (Oct 17, 2009)

precaud said:
			
		

> For the first time in decades, I am 602-less. Kinda weird.



Post-Jotul depression?


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## precaud (Oct 17, 2009)

Irrational, for sure. Guess you could say it had _cast_ a spell on me.  
My _steely_ resolve was quickly restored by lighting up the X33.


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## BrotherBart (Oct 17, 2009)

precaud said:
			
		

> Irrational, for sure. Guess you could say it had _cast_ a spell on me.
> My _steely_ resolve was quickly restored by lighting up the X33.



You were baffled I am sure.


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## precaud (Oct 17, 2009)

BrotherBart said:
			
		

> You were baffled I am sure.



Totally. But admittedly, that was secondary.


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## jeff602 (Mar 17, 2010)

BeGreen said:
			
		

> Durability is also a factor in fireboxes. It took almost 20 years for my Jotul 602's _inner_ burn plates to warp and crack. That's pretty durable and the servicing of them was fairly easy. The outside castings of the stove still look like new.


 where were you able to locate the side liners for an older Jotul 602 mine need replaced one is warped and cracked other cracked.


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## begreen (Mar 17, 2010)

I got them from Stove Parts Unlimited. See link for their catalog in the other thread that Rick spun off of this question. Local dealer should also be able to get them for you if that's more convenient.

Inspect the upper baffle plate closely as well. Ours was warped and needed replacing with the side plates after 20+yrs. service. The good news was that afterwards, the stove performed better than it had in years.


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## karri0n (Mar 18, 2010)

To this day, this is my favorite thread on hearth.com


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## Battenkiller (Mar 19, 2010)

This is a very interesting thread, one that I wish I was part of when it was unfolding.  Still, there is a lot of contradictory info given, with most of the techniques being useful to forge technology, where the idea is to keep the heat inside to keep temps up in the forging range.  The cook stoves mentioned, like the Rocket stove, are open stoves that work by getting the internal gases extremely hot so combustion is complete and greater efficiency is achieved.  In these designs, you are actually cooking over the searing hot flue gases themselves, not with heat conducted through the stove surface and into the pan bottom. Sure, you want high internal temps in a wood-burning heating stove as well, but you also want to get the heat transferred out of the firebox and into the room, not up the flue.

There was no explanation here of the physics behind the ability for ceramic insulation to simultaneously raise internal temperatures and still transfer heat efficiently through itself to the stove walls.  Temperature doesn't get transferred, _heat_ gets transferred.  All insulating materials work by slowing down the rate of heat transfer - period.  

My wife's glass kiln uses electric resistance coils embedded into low K-value insulated firebrick, which serves as the interior lining of the chamber.  Internal temps gets as high as 1400ºF, yet the steel jacket on the outside only gets a few hundred degrees, even if the stove kiln has been running all day at that temp.  If heat was efficiently transferred through insulating firebrick, shell temps of her kiln would get even higher that stove temps, yet clearly, this is not the case.

There are other inaccuracies as well, such as the color white being IR reflective, and this is simply not true.  White is reflective only is the visible range of the spectrum.  Refractory coatings like ITC-100 don't dry pure white and they do a fine job of reflecting IR radiation.  People often get these things confused because a black object gets hotter in sunlight than a white object, but that has to do with the enormous amount of visible light energy that sunlight carries.  Black things look black because they don't reflect visible light.  Don't assume this carries over into the infrared world.  According to the first law of thermodynamics, energy is always conserved.  If no visible light is reflected from a black surface, it must be absorbed.  The energy from the light will be converted to heat energy and raise the temp of the material.  It will then be emitted as IR radiation (or conducted into your hand, making it feel warm to the touch). That radiation will then strike other objects and change from radiant energy to heat energy.  The actual color of these objects is irrelevant to their ability to absorb or emit this IR radiation.  I'm not an engineer, so if any engineers or physicists here can show me I am wrong about this, I will gladly retract this statement.


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## karri0n (Mar 19, 2010)

Battenkiller said:
			
		

> This is a very interesting thread, one that I wish I was part of when it was unfolding.  Still, there is a lot of contradictory info given, with most of the techniques being useful to forge technology, where the idea is to keep the heat inside to keep temps up in the forging range.  The cook stoves mentioned, like the Rocket stove, are open stoves that work by getting the internal gases extremely hot so combustion is complete and greater efficiency is achieved.  In these designs, you are actually cooking over the searing hot flue gases themselves, not with heat conducted through the stove surface and into the pan bottom. Sure, you want high internal temps in a wood-burning heating stove as well, but you also want to get the heat transferred out of the firebox and into the room, not up the flue.
> 
> There was no explanation here of the physics behind the ability for ceramic insulation to simultaneously raise internal temperatures and still transfer heat efficiently through itself to the stove walls.  Temperature doesn't get transferred, _heat_ gets transferred.  All insulating materials work by slowing down the rate of heat transfer - period.
> 
> ...




The data shows here that it's not the _insulating_ or r-value we're looking for, but low mass and high refractory ability. Another factor to consider here is that most stoves do not have insulating material on every surface of the firebox, notably the stove top(which is where I believe precaud took his readings, and is often the most paid attention to surface on the stove in terms of heating). I'd imagine your wife's kiln is also not designed to be a space heater, and probably has either some shielding or some convective means that cools the outer surfaces. If not, I think the UL would take issue with a device that is not a space heater getting hotter than a space heater.

Bear in mind that the front glass is far from an insulator, and the entire flue gas path is generally designed for good heat transfer, with bare metal being above the baffle in the exhaust stream. I would also venture that, for a majority of stove installs, people aren't putting them in the center of a room where heat radiating outward from all sides is ideal. many people install a stove in a hearth or alcove, where radiant heat from the back and sides will be going directly into a wall, or worse, a masonry mass that has an exposed to outdoor surface. A higher internal temp, and more shielding on the back and sides, equals more heat into the actual living space.

Higher internal temps will always result in a cleaner burn,Though I can agree with you that if no other variables are changed, you very well may end up sending more btus up the flue this way.


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## PAJerry (Mar 19, 2010)

Very interesting thread!  I managed to get a box of PA-23 insulating firebrick from one of our suppliers (an advantage of working in a foundry). I had need for only 1 brick since one in the back of my Vista broke but he gave me the whole carton. Anyway, the new brick weighs about 1/2 as much as the originals.  I will be replacing the rest after the season is over so next winter will be interesting, seeing if the heat output, which is already very good, gets even better. I burn mostly slab wood since it is easier to use in a small stove, but when I have burned cord wood, I seem to get a lot of 'clinkers' rather than the fine ash.  Maybe the IFB will help in that regard.  If anyone wants to check, there is a lot of technical information at the BNZ Materials website. I had toyed with the idea of using 1" kaowool as a stove lining as it is amazing material - at work it can be red hot on one side and you can place your bare hand on the other - but it is probably too fragile to hold up long.  Maybe the IFB will do as well but hold up better.


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## Battenkiller (Mar 21, 2010)

karri0n said:
			
		

> The data shows here that it's not the _insulating_ or r-value we're looking for, but low mass and high refractory ability.



Not sure _what_ we're looking for, but Precaud is using insulating ceramic material for its insulating qualities:




> -The measure of this is called Thermal Coefficient, K for short. A high K says the material readily collects and stores heat. *A low K says the material is a good insulator, and resists the flow of heat through it*.
> 
> -As you can see, cast iron and the heavy firebricks are poor insulators. It’s no coincidence that they were widely used in pre-EPA stoves, when designers were trying to pull as much heat as they could OUT of the firebox. The *lightweight firebrick is the better insulator by far*
> 
> ...




The claim is that cast iron liners are inferior because of their poor insulating qualities, and that dense firebrick will only slow down the "response time of the system".  This is not explained, but I'm left to assume that these materials don't insulate but merely slow down the heat loss from the stove.  Well, that's all any insulator does.  A basic tenet of heat transfer is that heat will always flow from a material with a higher temperature to one of a lower temperature until equilibrium is reached.  Insulators can only slow down the rate of heat loss, not stop it.  




> I'd imagine your wife's kiln is also not designed to be a space heater, and probably has either some shielding or some convective means that cools the outer surfaces. If not, I think the UL would take issue with a device that is not a space heater getting hotter than a space heater.



The kiln is certainly UL approved if installed as per instructions.  I welded up a custom steel stand for it, and the kiln itself sits up on three insulated firebricks placed on their sides.  The insulating firebrick interior retains the enough heat inside the kiln that skin temps are relatively low.  Temperature is controlled with an infinite switch via a thermocouple and a programmable digital controller.  Without the switch and controller providing temperature control, both internal and external temps would continue to rise until the unit was producing as much heat externally as a space heater of the same wattage/BTU rating.  That's the beauty of using thermodynamics to analyze a system, the basic laws can never be ignored.




> Higher internal temps will always result in a cleaner burn,Though I can agree with you that if no other variables are changed, you very well may end up sending more btus up the flue this way.



Clearly, the EPA stoves work to give a cleaner and more efficient burn.  Hotter temps and correctly administered secondary air seem key to the non-cat stoves.  Many of the older designs achieved extremely hot temps in the primary burn zone the old fashioned way - by delivering air at higher velocities directly through the coal bed.  This also creates turbulence, which increases the mix of air and wood gases before they have a chance to escape the intense heat of the primary burn zone.  The only place I can see that insulation helps is in retaining heat in the secondary burn zone.  

A lot of thought and engineering has to go into this just to keep a few grams of particulate matter out of the exhaust gases.  The last chapter has not been written in this story, so I suspect that the stoves of 2020 will have more going on than the stoves of today.  I applaud all of the thinking that goes into these possible improvements.  All I am saying is that there are omissions in the explanation of how this material might improve a stove.  That is does improve a certain owner's stove in a certain set of circumstances... well, I'm not disputing the data that Precaud provided.  His thermometers did their job, and he dutifully reported the results here.  What the mind sees, the heart must believe.  I'm just not convinced it is happening for the reasons claimed.


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## maxed_out (Jun 14, 2010)

Well, I spent some time reading thru the firebrick discussions over the weekend and all I can say is wow!.   Its good to know I'm not the only one pondering this stuff.  Good to know one is not alone. 

Anyway, its time to order firebricks for the (used-2007) Quadrafire Isle Royale.  My first season with it!   Theres a couple cracked and the back ones with the holes are pretty bad.  So after reading thru the thread, I have to ask which ones should I use?  Pummice, clay or other.  Clay on bottom? pummice on sides?  Fire away.

The guy I got the stove from seemed to think there is some type of upper firebrick required.  I havent seen a real live stove or studied the pics enough to know. If anyone can help me with this let me know as well.

thanks!


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## precaud (Jun 15, 2010)

I'd stick with the pumice brick. No clay. You can safely move the broken/cracked ones to the bottom, ash will fill them in, no problems. You probably will have to buy the ones with holes drilled.

I don't think there is "upper firebrick" on these, it's most likely a high-temp ceramic fibre board. You can download the users manual for your stove on Quad's website, all the details should be in it. Enjoy your stove.


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## maxed_out (Jun 15, 2010)

precaud, thanks for your advice and all the testing and sharing you've done on this topic. Been an eye opener.   I'm headed for the pumiced land.


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## maxed_out (Jun 18, 2010)

Just a brief update on this QF IR.  I'm finding the pumice firebricks really easy to work with and cut.  I setup my radial arm saw with a masonry blade-cuts very well. Some dust so if your travel this road do it outside.  I used a small masonry bit in my drill, made a swiss cheese hole pattern and knocked out 2 pretty good if I dont say so myself holes.

The upper baffle refractory-above the air tubes?  Dealer wants 50.  Is that what I want to do?  I thought I saw somewhere in this thread another source but that remains elusive.  If anyone knows a source or another means to save any $ over the dealer quote please post.

I think after I get the baffle in, she'll need some of that stove magic wipe on stuff and then bring on the cold.

Oh yeah forgot to ask...35 for fiber handle also seems harsh.  Anyone got a better way here as well?


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## vvvv (Jun 18, 2010)

if the wood gassifies too fast for the available supply of combustion air its an inefficient burn


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## precaud (Jun 18, 2010)

Well done, maxed. Did you buy the pumice bricks from Quad? How much were they?

Pricing on the fiberboard baffle is a hard call. So far, noone has been able to find a place to buy small quantities of this stuff, except through a dealer. It's higher density than the stuff available through normal retail channels. 50 doesn't impress me as a terrible price.


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## maxed_out (Jun 18, 2010)

The bricks were 5 a piece from the dealer.  The 2 piece set with the holes were 30 for the set so I saved a little there. I think I have enough bricks that if needed I could go 2 deep on the bottom.  Who knows what thats gonna do.

On the baffle, do you think kaowool would work? Maybe thats more of a insulator than a refractory material.  I guess I could use a clay sheet of firebrick if I could get something close to the right thickness.????

Or you can stop me from trying to jump thru flaming donut holes and just buy the sheet from the dealer.


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## precaud (Jun 18, 2010)

Why would you want to go 2 deep on the bottom? Only makes your firebox smaller.

Kaowool is too soft, it has poor abrasion resistance. I get away with it in the X33 because the firebox is so tall and wood never even gets close to it. In your Quad it would get chewed up in no time. The standard baffle material is a high-density version of Kaowool. No clay! Just buy the sheet and be done with it, and don't jam wood into it when loading. If you have any 1/4" kaowool blanket laying around (every household should...) put a layer of it on top of the board. It seals any leaks around the edges of the board and provides more insulation. Quad started doing it on most models a few years back.


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## maxed_out (Jun 19, 2010)

precaud, On the bricks just me being thrifty!  I'll put them away for a rainy day.  

Kaowool on top of the board.  I'll do that.


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