Whats the Difference Between a Wood & Coal Stove?

Whats the difference between a wood & coal stove? I have a wood stove now but wanted to set it up for coal. Ill take some pictures and get them up soon. Is it a pain in the A** to convert? Its a Nestor Cast Iron Stove...

Thanks Tom

Welcome to the FORUM Tom. Does your stove have grates inside & a form of shaking them to get the ash down below the firebox?

Without going into a lot of detail...the biggest differences are the way the air enters the stove, and the firebox/grate design. Like Fred posted, a coal stove must have a cast iron grate and a way to shake the ash out of the coal bed...the air must come up through the grates and through the coal bed.

Yeah. My take is that a coal stove need a shaker mechanism to clear out the ash and a separate lower air intake to allow the air to flow up thru the coal. Generally a coal stove will burn wood but not necessarily viceversa. My coal stove burns wood fantastic. Not as long as a wood burner, but the wood burns up great.

The saying goes you can bun wood in a coal stove but you can't burn coal in a wood stove. While on the topic be wary of anything labeled as dual fuel from any manufacturer that is primarily in the wood burning business in particular the wood boilers. Research because many of them are problematic with coal. Also note that most coal burners can't be labeled dual fuel because of EPA regs and overall are not as efficient burning wood as a wood burner. Be sure to search here before purchasing anything labeled dual fuel, there is only two I'm aware of that people have been very happy with. The Harman TLC and e-f-m's wood/coal boiler. That's not to say there isn't others that work well.

Ideally a coal stove has a deep firebox, all the combustion air coming from underneath and vertical sides so the entire bottom of the firebox is grates. the grates need to be shaker grates. The "deep" firebox isn't an absolute must because there is some design like the Franco Belge that work fine where the coal is more banked against a back plate, those have an auto feed hopper inside the stove that supplies new coal through gravity. Some coal stoves do come with draft over the fire but that is primarily to burn off the gases before you open it up so you don't lose your eyebrows. See this topic here: Minor Explosion in Coal Stove

Here's an example of the ideal coal burner, the e-f-m wood/coal boiler:
The efm WCB-24 hand fired wood/coal boiler

Richard S. wrote:. Also note that most coal burners can't be labeled dual fuel because of EPA regs and overall are not as efficient burning wood as a wood burner.

Hi Rich, I was always wondering about the efficiency of burning wood in a coal stove. My Hitzer is supposedly a 80-90% efficient stove ...

I have burned wood while starting a stove but never noticed a significant amount of heat from it...I would guess its 50% efficient...any thoughts?

I'm becoming convinced that under idealized and well controlled short term laboratory conditions wood and coal stoves (plus boilers, and furnaces, hereafter called etc...) can be made to achieve efficiency levels of 80% plus, but in the long term 24/7 real world conditions where we use them wood stoves (etc...) are closer to 50-55% efficient and coal stoves (etc...) are closer to 60-65% efficient. A coal stove burning wood is something where I have no experience, but I can see where it might be problematic as to efficiency. I've burned wood for decades (sometimes exclusively), and I'm only heading into my second heating season with exclusively coal.

davidmcbeth3 wrote:
Hi Rich, I was always wondering about the efficiency of burning wood in a coal stove. My Hitzer is supposedly a 80-90% efficient stove ...

I have burned wood while starting a stove but never noticed a significant amount of heat from it...I would guess its 50% efficient...any thoughts?

I couldn't begin to guess. I don't know enough about wood.

lsayre wrote: but in the long term 24/7 real world conditions where we use them wood stoves (etc...) are closer to 50-55% efficient and coal stoves (etc...) are closer to 60-65% efficient.

You might be interested in this topic with a two year study on the Axeman Anderson which I believe is same design as the AHS.

Bureau of Mines Report 4936 Axeman-Andersen Anthratube Boiler

Page 10:

EFFICENCY OF EQUIPMENT
Table 2 shows an approximate heat balance when stabilized burning
conditions have been reached after starting (fig. 23 and 24). The number of
minutes before such conditions are reached after starting depends to an
appreciable extent upon the condition of the fuel bed or the length of time
of the off-period just before the start, For the conditions shown in figures
23 and 24, an efficiency, as related, to heat for space heating and domestic
hot water, of about 76.5 percent is reached after about 1 minute. The
efficiency continues to rise for about 4 minutes and then levels to about
the figures shown in table 2, item f, or 81.6 percent for Pea and 84.0 for
Buckwheat. The chief reason for the somewhat better efficiency of the
Buckwheat coal is the better burn-out of combustib1e in the ash. If the heat
radiated from the boiler and connecting piping is useful, the efficiency, as
related to heat to water in the boiler, is expressed by item h in table 2,
or 84.0 percent for Pea and 86.7 percent for Buckwheat.

With a wood stove, you can only get your chimney to catch on fire.

With a coal stove you can blow the door off your barometric damper.

When you're really good with coal, you can blow your whole stove pipe assembly apart.

Not that I know anything about that personally, but people talk ya' hear things.



So coal vs. wood is really just a matter of personal taste - a roaring 25' vertical inferno vs. a house rattling 'boom!'.

Glad to clear that up for you, keep asking questions, it's the best way to learn!

I think for the AA and AHS it is the idle times between firing that bring down the real world system efficiency. I noticed that in the depths of winter I ran at much higher efficiency overall than for any of the warmer months. In the winter I measured my efficiency as lbs. of coal burned per heating degree day, and for the coldest months I was at about 1.57 lbs. of coal burned per heating degree day. My thinking is that if we get a real winter this season it will be overall quite beneficial from an efficiency standpoint. I agree that when the fan is running more frequently they are very efficient. Running mine all summer has taught me that efficiency during this period is pretty bad overall, since it is rarely firing. For the summer months I've burned about 15.5 lbs. per day both to make DHW and keep the fire going, but on a BTU basis it probably only takes the BTU's of about 3 to 4 lbs. of coal to daily heat our DHW, so about 11-12 lbs. per day are lost to idling and maintaining the fire. That's efficiency in the range of only about 20-25%.

When we were all electric I figured over a period of years that I was using overall about 3.333 KWH's of electricity per heating degree day, for our homes combined heating and DHW during the winter months. Our average KWH per year was 27,000, and appx. 7,000 were for everything but heat and DHW. 20,000 KWH/6,000 HDD's = 3.333 KWH/HDD

3.333 KWH's/HDD x 3412 BTU's/KWH = 11,373 BTU's consumed per heating degree day (HDD)
This was both the input and output BTU's if electricity is 100% efficient

1.57 lbs. coal/HDD x 12,230 BTU's/Lb. = 19,342 BTU's/HDD
This was our input BTU's for coal, and with output BTU's for heating and DHW still being held at 11,373 this becomes:

11,373/19,342 = 59% efficiency for coal during the winter months in my case

But for electricity we maintained the house at 62 degrees much of the time, and at 68 degrees only when we were awake and actually at home. With coal we keep the house at 68 degrees all the time. Taking this into consideration, I'm guessing the coal to be 65% efficient.

I agree. To get the highest efficiency the stove has to be fired at the one point where combustion efficiency is highest. This also requires a uniform feed to maintain that point. To do otherwise is to generate excessive carbon monoxide if the air is throttled too much or stack loss with too high a fire.

Avoid a wood/coal stove where the firebox is shaped in a V. The slanted sides do not work well when burning coal.

Kielanders wrote:With a wood stove, you can only get your chimney to catch on fire.

With a coal stove you can blow the door off your barometric damper.

When you're really good with coal, you can blow your whole stove pipe assembly apart.

Not that I know anything about that personally, but people talk ya' hear things.



So coal vs. wood is really just a matter of personal taste - a roaring 25' vertical inferno vs. a house rattling 'boom!'.

Glad to clear that up for you, keep asking questions, it's the best way to learn!

That's funny!

Isayre, what does per heating degree day mean? How do you calculate it?