Whats the difference between a wood & coal stove?

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.

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.

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!