Temperature Of Wood Coals...

Peter B. · Feb 27, 2008

Hello... brand new here.

I've searched both here and on the web, but can't find an answer to this, maybe because my search terms are too vague.

I'm wondering what the (approximate) temperature immediately above (within 2-3 inches) a good hot bed of wood coals might be?

Say when the stove temp is still high, but it's time to reload?

--

Though it's not necessarily relevant to my question, I'm running an antique parlor 'smoke dragon' that I've retrofitted in various ways for improved efficiency and safety. Probably no where close to an EPA stove, but much improved over the original straight-through design.

Thanks for your time... and an interesting forum.

Peter B.

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BotetourtSteve · Feb 27, 2008

Hot enough to burn the h-ll out of your hand if you're not careful while reloading!

Corey · Feb 27, 2008

Kind of depends on the coals and the air hitting them. If you can judge the approximate color:

https://www.hearth.com/econtent/index.php/wiki/Temperature_when_metal_glows_red/

This chart will give you the approximate temp. Maybe deduct a couple hundred degrees since you ask about a couple of inches above the coals. Of course if the coals are orange-hot and being fed by a good draft from below, the temp above the coals may be nearly as hot as the actual coal.

Peter B. · Feb 27, 2008

BotetourtSteve said:
Hot enough to burn the h-ll out of your hand if you're not careful while reloading!

After over 30 years burning wood, I'd got that much figured out, I guess.

Hoping for a more 'scienterrific' answer if anyone here can provide one.

The reason I ask is that one of the modifications I made to the stove is an internal baffle that drops the smoke inlet to within 4-6 inches of the firebox floor, then sends the smoke through another chamber and a catalyst (inside the stove).

Just wondering if the temps near the coals (and the baffle inlet) are close to those necessary for secondary combustion... and yes, I've added a secondary air supply as well.

Thanks.

Peter B.

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Peter B. · Feb 27, 2008

cozy heat said:
Of course if the coals are orange-hot and being fed by a good draft from below, the temp above the coals may be nearly as hot as the actual coal.

Corey:

Thanks for this... more what I had in mind... not that I don't have a sense of humor.

So you think the temps corresponding to metal colors apply to the color of wood coals as well?

(I see you got 'creative' with a smoke dragon as well. Does it work well?)

Peter B.

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kellog · Feb 28, 2008

Could you mount a metal bar at the point you want the temperature measured, let it heat up to temp and then use an infrared thermo to measure the temp of the metal bar?? I suspect the temp 2-3" above hot coals is higher than most inexpensive contact thermos read.

Martin Strand III · Feb 28, 2008

Elementary, my dear Watson.

Stage I: Water is driven out of the wood

Stage II: @500* F wood chemically breaks down, vaporizes volatile matter

@1100* F vapors ignite and burn (major source of heat here and why it is important to burn hot)

Stage III: >1100* F charcoal burns

Ref: http://www.montana.edu/wwwpb/pubs/mt8405.html

With a large hardwood fuel load [50 lbs], my TempCast literature says temps can get to 1800* F or above in the middle of the firebox where the coals appear almost white hot. It seems reasonable since it easily maxs out my handheld infrared BBQ thermometer which has a max readout of about 1250* F. These temps will damage metal stoves if maintained for long and is dangerous. The incoming air requires dampening to operate metal stoves within the MFG's guidelines.

Aye,
Marty
Grandma used to say, "When you're hot, you're hot. When you're not, you're not."

Peter B. · Feb 28, 2008

kellog & Marty S:

Thanks to you both...

I'm likely to pick up an infrared one of these days, but I'm mostly just 'playing' at the moment and thinking about ways I might improve the retrofit modifications. I've used the same setup for quite a few years, but the stove could use an overhaul and I'm trying to decide what to change and how... this summer or fall when I get to it.

Last night, using a conventional probe thermometer I switched back and forth between the flue (at 12" from the stove top) and the internal temperature of a chamber I built into the top of the stove where the smoke passes before heading up the flue. The chamber is 'fed' from the baffle I mentioned before.

When the flue was in the 400-550 range, the chamber temp ranged between 700-900. I've got no way of knowing at the moment, but I'll bet there's a comparable difference between the chamber temp and the baffle inlet near the firebox floor... which means there *might* be at least 1000+ at the baffle inlet... that is, with a good bed of coals... and since anything leaving the firebox has to pass through the baffle...

The chamber normally houses a catalyst, but the slide I built for it isn't working smoothly at the moment, so...

After a good hot fire (even throttled down for the night), the residue left in the upper chamber is light cream to white which suggests to me the burn is fairly clean... even without the catalyst.

I still make some creosote, and have to clean the chimney once or twice a season, but most of the creosote forms in a black pipe offset upstairs between two runs of Class A... that I can brush from inside.

I just wish I could *see* the dam fire sometimes... I think that's the only reason I'd trade up to a modern stove. All the modifications I've made have been done 'blind'.

Thanks to all for your help.

Peter B.

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jadm · Feb 28, 2008

Are metal temps. the same as wood temps?

Martin Strand III · Feb 28, 2008

perplexed said:
Are metal temps. the same as wood temps? I get white hot coals in the center of my insert - approx. 4” in diameter - Rutland therm. reads 400* on door. I am confused again.
I thought that when manuals warn against overfiring and mention seeing red they were referring to metal parts turning red.
Are you referring to the entire bed of coals burning white?

Metal starts to turn red, a sign of over firing, about 900* F. In my experience this usually happens at the beginning of the flue where the volume of hot burning gases in the firebox is choked down to a smaller volume of the flue. I have also seen it in a wall of a metal stove. The fire has to be much hotter than the metal to do this.

The "white hot coals" I have seen have been a relatively small area, maybe baseball size, entirely in the middle and later in the fire. I build my fires crisscross fashion with an inch or so air space between splits. Somewhere between Stage II and III (see above post) involving charcoal burning, the partially collapsed burning stack is still visible. The air spaces in the center of the stack seem the hottest and appear almost white. This seems really hot; much hotter than 'red hot'. I've learned not to get too close gawking thru the glass at this point to save singeing brows not to mention my short ones.

I'm sorry you're "confused again", perplexed. I hope this helps you get it straight.

Aye,
Marty

jadm · Feb 28, 2008

Marty- Now I am unconfused because that is what I thought it meant. I never had the white hot coals in my other unit so this is new to me and happens just as you described. Thanks!

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