gorms

I've got 3 wood stoves in my house, and one in the garage (spare). I have an insert w/blower that runs just about non stop below 40*, big honkin old Vermont Castings (takes a 36" log), and one in the basement I only use when well below zero. Electric heat and a big 18th century farmhouse is not a good combo for the wallet! It's been a nice, cold, snowy winter so far so I've burnt a good 3+ cords so far and I'm getting low.

My dad said he can get his hands on 3-6 tons of coal for free out of an old dry barn. I've had a woodstove wherever I have lived for several years, never seen anyone with a coal stove though. What is the difference? Can I burn coal in a wood stove? How does it affect the chimney/liner? I've got a 8" stainless liner inside a 10x12 ceramic lined chimney for the insert, the big one stubs up and into an 10x10 ceramic flue, less than 10 years old. I would only consider burning in these two stoves. Any thoughts?

Mexstan

Interesting question. I Googled your question and discovered that there is quite a bit of info out there on this subject. Here is one answer:

I was wondering what the structural differences were between coal and wood stoves. Is there a reason you can't use coal in a wood stove, or visa versa? Thanks.

-- Amy Leone (aleone@amp.com), September 03, 1998

Answers

Amy, I have used both. The major difference between the two is the addition of a 'shaker grate' in the bottom of the stove along with a clean out door underneath it.

Wood does not care where it gets it's air from. It will burn with a draft from the top of the fire. It burns better with a controlled draft from the bottom or side, but it will still burn. Coal MUST have a draft from underneath the coal bed. The grate is there to support the bed of burning coal so air can enter from underneath, and it shakes so the coal ash can be shaken down into the bottom of the stove for removal.

We get about 80% of our winter heat from a small coal stove in the basement. If we carefully control the air flow we can keep the stove going for weeks at a time without ever letting it go out. Shake it down, refill with fresh coal, clean out the ash.....twice a day with ours. Care must be taken with the hot ashes which can have live coals in it.

Stoves can be had that burn both wood and coal. That's good and bad. One feature of a true coal stove is the depth of the fire bed. A long burning and efficient coal bed must be deep. Ours is about 14 inches from grate to top of the fire brick. A full load of coal is about 40 pounds. Wood stoves usually don't have such a deep and narrow bed. They don't need it.

A coal stove will burn chunk wood just fine. It won't burn as long as the coal would, but it will work without a problem. A wood stove will almost never burn coal correctly. Even if the wood stove happens to have a shaker grate (many high line ones do) the grate will usually be too course to support a coal bed.

Another difference: Wood stoves will build creasote in a chimney unless carefully managed. If it gets regular maintenance and is run at a decent tempurature that's not a huge problem. Let a lot of creasote build up in a chimney and you risk a runaway chimney fire and possible severe damage. I have had this happen. I put mine out by setting a BIG pot of water on the fire and closing my fireplace doors. The combination of steam and lack of air shut the fire down.

After a good friend (an accountant) died I used to go over and maintain the wood stove for his wife. I would sit in front of the stove and shovel in IRS forms to get a good roaring fire going and burn out the chimney. Lots of satisfaction in that. Jon would have enjoyed it.

Tip on running a stove, either coal or wood: Leave a layer of dead ash at the bottom to insulate the stove from the worst of the heat. It will greatly enhance the life of the stove. The grates can take high heat, but not forever. They will eventually warp or crack.

No matter which kind you get, buy a chimney thermometer and use it. Get a magnetic one and learn where on the stack it gets the best reading. Usually close to the stove. You should also consider an automatic self adjusting flue vent. It will react to stack air flow and compensate for exterior wind conditions. In high wind conditions I have seen our stack flue go wide open and STILL have the stove get way too hot. If a high wind comes up it can literally suck the exhaust up your chimney and turn your nice calm stove into a blast furnace.

pind

I am not going to say its all about the firebox, because the flue plays a large part, however... Coal burns HOT, compared to wood. If a proper coal furnace, you'll see temps of up to 1600 degrees. This comes from working in a plant that used coal fired drying units for the ore concentrate, prior to shipping.

Temps that will reduce most mild steel stoves to a puddle of their former selves. I have seen coal burned successfully in brick lined stoves, with ceramic flues, but not in anything else thus far.

Homesteader outdoor boilers have models that are built to burn wood or coal, at the users discretion, and I can tell you that the inner construction of those is FAR different than the regular wood only model.

I have a Clayton stove, that is brick lined, with cast iron shaker grates in the bottom. It is supposed to be able to handle coal, but I am not interested in trying it.

If you choose to experiment, be careful. I would rather go for more wood.

Good luck

BarryG

While I dont know the differences I do use a coal stove in a mountian cabin in Utah. This stove is a true cooking stove it also has an oven and is not something like a pot belly stove. One feature that is way cool at least for us with this stove is it also has a water jacket in it so you can use it to heat your hot water. The stove is made from cast iron and is very heavy of course it is also from the 1920's. In the above post where it mentions the shaker grate. The shaker grate in this stove is made of cast iron and is a two piece deal that have interlocking teeth (sort of like two combs meshed together) these teeth are approx 3/8 inch wide and 1.5 inches long and an inch thick that intermesh and as you rotate the handle it rotates the grate which move the teeth. Just moving the handle back and forth a bit shakes the coal. Which also allows bigger pieces to fall through into the ash box below(well bigger pieces than you really want in your ash bin). The grates and firebox get very hot. The grates in this stove weigh in the neighborhood of 40lbs. One problem we have had is the grates warp which keeps them from being able to be shaken well or even moved at all at some point. Fixing or replacing them is an arduous task due to finding replacements since no one makes them at least for this stove. As far as a flue and stove pipe it just uses standard stove/flue pipe and we use a section of double wall as it goes through the ceiling/roof. Our pipe is made from stainless and is discolored from the heat. The flue damper itself is also cast iron and weighs a few lbs. I would see no problem burning wood in a coal stove but am unsure about burning coal in a woodstove due to construction and air flow. If it were me I would try and call the manufaturer if that is possible.

We also have some pot belly type stoves in other buildings up there and they also work fine for wood or coal as we burn both in them but they do have raised grates and can get airflow from underneath the grate.

Redleg

Maybe list the coal on craigslist and use the funds to order some wood? Old coal burners get used all the time for wood (I have a large, 4 legged, cylinder stove in my living room). But like mentioned above, I don't think it's easy to maintain a coal fire in a wood burner without modifying the venting. Also later stoves and chimney pipe may not be able to handle the hotter temps of the coal. There might be an old engine club near you that might be interested in that coal.

Bark

We can get free low grade coal from a seam that is eroding into the ocean. We used to throw a small hunk (five lbs or less) in with a load of wood. Got carried away and put in too much coal and destroyed the grate on the bottom and got really hot. No more coal in a wood stove for me.

SIXSLUG

For some reason I am remembering we were told not to burn coal in our woodstoves in MT.

gorms

Thanks for the info guys. Maybe I'll try mixing a little in with the insert, it's lined with 2" thick firebrick all around, and has 3/8" steel all around, very heavy for a small box. Holds heat well. If it's too much of a pain maybe I will just try selling it. The blower on it moves something like 2-300 cfm on high, helps cool it down when it gets too hot pretty quick. Just filed taxes and getting a good return this year so now I can afford to buy some more, which I can't stand doing but it's cheaper than electric still.

ghenges

You can burn coal in a stove designed for wood -- if you are careful.

I have been firing coal furnaces since the 1940's.

The most important thing is to keep the coal off the grates, be especially cautious if the grates are made of steel.
Coal burning furnaces have cast iron grates.
When firing a coal stove it is mandatory to keep a bed of coarse ashes between the coal and the grates.

Coal varies widely in quality, if the coal you are obtaining has been stored for years is likely to be gassed out and won't burn as with the heat it's capable of. However, that may be an advantage in your circumstance since it's unlikely to burn wild.
(Sometimes with new high quality coal the gas cooks out making a thick greenish tinged smoke, when you open the stove door the oxygen makes it explode mildly.)

My advice would be to mix the coal and wood for a while until you learn how much heat you coal will generate.
My brother burns wood all day in his stove and banks it with coal shortly before retiring for the night.
You will enjoy a coal fire, if properly banked, it will still be going in the morning.
Be cautious banking an overnight fire because it can catch and run away. I've been woken many a night hearing the roar of a runaway fire because weather conditions changed causing a better draft than anticipated.

You'll learn quickly how to fire with coal, it's like anything else, you have to do it to learn it. Only two variables -- fuel and air.
One thing you won't like is hauling out the ashes.

I have seen hundreds of coal furnaces with a bulge just above the fire brick line because the furnace got so hot the steel softened a sagged from its own weight.
Just keep the direct fire intense heat away from bare steel. You indicate your stove is constructed of 3/8" steel, that's great. Steel coal furnaces (round) were mostly 1/4" and less.
I have a cast iron coal furnace with its "kidney" on the top down in the garage. I've misjudged the coal charge in that stove and it got so hot the metal above the fire brick line was nearly white hot, yet it never did any damage.