# Chimney Temperature coal vs wood



## coldinnj (Nov 9, 2006)

I believe I have heard often that coal does not produce as hot a temperature going out the flue as wood. Specifically when they are  referring to danger of chimney fires.
True coal will not produce the creosote buildup in a chimney that wood will however...
At one time the temperature of the air above the fire in the firebox with my old coal furnace was measured.  It was over 1700 degrees.
I am aware that there are many ways of "over firing" your furnace / stove but does wood produce a temperature even close to that? In a stove of course, not talking wildfire here.
In an overburn situation it has already completely melted off the end of my poker. Also melted off the baffle plate. 
I learned a valuable lesson not to let the uneducated tend the coal furnace. "Children shouldn't play with matches"
Anyone have the max temperatures of the different fuels as far as the exhaust of combustion gases is concerned.


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## Corie (Nov 9, 2006)

Air above the fire in the firebox and the actual stack temperature are two completely different animals.  Remember that secondary combustion in a wood stove is occuring at 11-1400 degrees right below the baffle, yet the chimney temperature just a few feet above the firebox may only be 300 degrees.

The thing with coal combustion is that the combustion occuring in the firebox is so complete that very little combustion byproducts, ie heat, make it up the chimney.  Same thing with the modern wave of wood stoves but to a slightly lesser degree.

You know the temperature in the firebox was 1700 degrees, but did you ever check the stack temperature? Generally, when our coal stove is running at 500 degree body temperatures, the stack temperature may only be about 200 degrees.


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## laynes69 (Nov 9, 2006)

Thats the thing, Poor coal like soft ohio coal is high sulfur, and its very dirty. You have to worry about soot and ash accumulations in the flue and the chimney. Also at times the flames can be intense. Now burn high carbon low sulfur Hard Coal, and you have a smoke free smell free fire. Stack temps can get so low that you can hold your hands on them, not for long, but a huge difference than wood. The one thing that I was always curious about, is whats the difference in temps in the firebox itself? I am pretty sure coal will produce alot more BTU'S than wood, Or at least burn much hotter. I like hard coal for the long cold nights, When I dont want to get up to feed the fire at 2:30 in the morning to keep the house up to par. I remember one time it was probably 10 degrees out and snowy and windy. I loaded up the wood/coal furnace at 7:00 pm and I woke up at 7:00 am and the house was 80. That would have never happened with wood. It would have burnt up alot sooner. Still wood is my main heat.


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## Corie (Nov 9, 2006)

Coal has the ability to produce more BTU's per pound.  Coal is denser and is more carbon than other substances.  An 80lb load of coal inherently holds more carbon than an 80lb load of wood and thus has the ability to produce that many more BTU's.  Also, some wood heat is wasted in the evaporation of the moisture in wood whereas these is little, if any moisture contained in coal.


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## coldinnj (Nov 9, 2006)

I understand and agree.
Always knew coal had more BTU's.
However as this is a very old coal furnace I am still curious as to how hot the combustion air is going into the chimney 
Under conditions using the older hard anthracite coal: Air approx 25" above coals in firebox was 1700 degrees. Then the air must travel out and down throught the "kidney" then out into an 8" "stack" pipe which runs 17' horizontally (with a pitch of course) till it reaches the chimney then the flue on that side of the chimney is 7" x 12" which runs approx 30' up. I never measured the temperature in the stack pipe. Now that all I get is "garbage" coal I don't know if the temps will tell me anything.
When it was running correctly although the urnace is insulated well enough around it that you can lay against it with no problem the stack pipe was the only heat in the basement  yet it kept the almost 1300' uninsulated stone wall basement cool but comfortable enough.
So I still wonder...
Does an old coal or wood burning furnace / stove produce greater heat at the chimney?
Remember I am not comparing to todays modern, efficient devices.


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## berlin (Nov 9, 2006)

"Does an old coal or wood burning furnace / stove produce greater heat at the chimney? 
Remember I am not comparing to todays modern, efficient devices"

no. coal will always be hundredse of degrees cooler at the stack than wood, whether it's soft coal or hard coal, compared to wood coal will always be much cooler.


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## coldinnj (Nov 10, 2006)

Thank you Berlin


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