Why Use Firebricks?

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dsteinel
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Post by dsteinel » Tue. Feb. 24, 2009 6:27 pm

I have been using a Vigilant Wood burner for several years and am going to move over to coal. I would get a coal fireplace insert. My question: why do coal stoves/inserts have firebricks in them? My wood burning Vigilant does not have firebricks inside and it works fine. What is the function of the firebricks in coal stoves? Where should they be? Don't they keep heat from being transferred to the air in our room and doesn't that make the stoves less efficient?

 
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grizzly2
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Post by grizzly2 » Tue. Feb. 24, 2009 6:46 pm

Good question. My first woodstove was cast iron and did not have firebricks, both sides cracked (It was also a cheap stove). My second cast iron wood stove did have fire bricks. I never had any problems at all with that stove. My third cast iron woodstove had cast iron baffels in the back and sides, presumably to keep the wood coals out of direct contact with the outside of the stove. The back baffel warped and cracked badly.

Anthracite coal burns hotter than wood, at least in a stove environment. The firebricks keep coals from touching the cast iron or plate steel of the stove body in order to prevent overheating of the iron or steal. Overheating can lead to warping, cracking and burn through of the stove material.

Is there any efficiency lost? I don't know. The heat absorbed by the bricks still radiates into the stove sides and thereby into the room. I suppose the intense heat that is not transferred to the stove sides is part of the heat that circulates throughout the rest of the stove, some of which heats the rest of the stove and some of which probably does go up the chimney.

I will be interested to see what others have to say.

P.S. Once you get used to burning coal you will find it is a fraction of the work of burning wood. :)

 
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VigIIPeaBurner
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Post by VigIIPeaBurner » Tue. Feb. 24, 2009 7:20 pm

grizzly2 hit on the main points. I've seen others post the fusion temperature of anthracite coal, that temp at which it's likely to form clinkers, at ~ 2600 F. That's too hot for contact with typical cast iron types that has a melting point around 2100+ F. The ceramic fire brick act as a thermal mass to even out the temperature and insulate the iron surface.

I had a wood fired VC Defiant for a long time. The stove top temperate ran around 300 F +/- if I recall, it's been a while. I used the Defiant for 20 + years and when I left it behind when we sold the house, the firebox looked the same as the day I installed. I'm enjoying coal heat a lot more. The VC Vigilant II I have is fire brick lined. The Vigilant's operating temperature 400-700 F as measured on the stove top. I run consistently in the 650 -700 range. This stove is in its seventh season and I re-bricked it three years ago. The front grill is cast iron and hold the coal away from the glass. It began to sag between the supports on year 5 when I over fired the stove - oops :eek2:


 
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oliver power
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Post by oliver power » Tue. Feb. 24, 2009 8:44 pm

Yes, Grizz has it covered.

 
z28camarojim
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Post by z28camarojim » Fri. Nov. 04, 2011 10:45 pm

I have a question if its possible to be answer I have a monarch wood coal add on furnace and it has cast iron liners in it which are pricey and I remove all of them ( because there all cracked and warped ) and replace them with Just fire brick will it be safe to burn wood and coal in without warping and cracking the fire box ? Thanks ahead of time for the answer!!!

Jim

 
franco b
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Post by franco b » Fri. Nov. 04, 2011 11:02 pm

dsteinel wrote: What is the function of the firebricks in coal stoves? Where should they be? Don't they keep heat from being transferred to the air in our room and doesn't that make the stoves less efficient?
Aside from protecting the stove from excessive heat an important function is to keep the heat in the fire pot which contributes to more complete combustion with less excess air needed. Air in excess of the minimum needed only carries heat up the chimney. The function of the fire pot is to burn the fuel, the function of any heat exchange area is to transfer it to the room. The two functions are separate and the more they share those functions the less efficient the stove will be.

Look at the pictures of the Crystal stove in this forum. You see a well insulated fire pot and a very large heat exchange area as well as provision for even more heat exchange. That stove should be very efficient with minimum production of carbon monoxide.

Many modern stoves increase heat exchange efficiency by the use of a blower.

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