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Anthracite Coal For Cold Weather

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ChrisOlson:
It's 4 below here tonight and supposed to be 15 below in the morning.  When it gets below zero we switch from wood to anthracite stove coal in our furnace.  We have a central forced-air Daka high efficiency combination wood/coal furnace, built in Pine City, Minnesota.

If you've ever tried to burn anthracite, you know it's almost impossible to get the stuff to light and burn.  It's like 86% pure carbon - a few more million years and it would diamonds.  And when it burns it has no flame (except for some blue flame right at first when the coal gas gets driven off it).  It just glows.

Anthracite is the cleanest burning fossil fuel known to man.  It emits no smoke, no particulates, nor any odor when it burns.  There's only two problems with it - getting it to light, and extreme BTU output once it is burning.

I had a nice hot bed of hardwood coals on the grates in the furnace tonight so I threw in three shovel fulls of anthracite, one at a time in layers.  You have to "light" it in layers using the bed of hardwood coals with full draft under the grates.  It takes about 30 minutes to get each layer of coal lit, then you add another layer and spend another 30 minutes getting that hot enough to start glowing.  I usually put in three layers for a new coal bed.  It's important for burning coal to have draft air both above and below the coal bed.  The draft air from underneath provides combustion air, the top draft provides combustion air for the coal gas that gets driven off while the coal is heating up.  Once the bed is glowing good, the top air is shut off and only bottom draft is used.

The furnace has to be on manual control for draft to get it going.  The stuff burns the chimney slick and clean as a whistle.  If the chimney is coked up from burning wood in the furnace, it usually gets a chimney fire going first.  I let the chimney burn until it gets to critical temperature, then close the air off and kill the fire in the chimney, let it cool down, then turn the air back on to get my coal going again.

The blower on the furnace has to be running all this time to keep the firebox temperature at a safe level.  By the time I spend roughly two hours getting the chimney burned out , and the new coal bed burning and stable, it's so hot in the house my wife has the windows open.  This is why I don't even mess around with anthracite in warmer weather.

Once it's going, and stable, life is good.  Only have to fire the furnace once a day in 20 below weather.  And firing it is a 30 minute job every day.  Shake the coal bed down, put the furnace on manual and add a new layer, clean the ash pan out, and leave it on full draft until the new coal is going and glowing red all the way thru.  Then close the draft down, put the furnace back on automatic, walk away and she's good for another day.

Last year, with two solid months of sub-zero weather I started a coal fire in January and it burned until the February when we finally switched back to wood.  This year, with Global Warming kicking in, this is the first day we've burned coal this winter.
--
Chris

bj:
   From the sounds of all that Chris, I'd say your house doesn't waste a lot of heat either.
   Half an hour of work for a day of heat, is pretty human energy efficient as well

Wolvenar:
I have similar issues here.
Unless the temps are consistently below 0F I cannot fire up either of the wood furnaces and easily keep them controlled.
Either setup burning wood works well under 0f but it makes for a lot of futile work trying to keep the house a comfortable temp with outside temps of 0-30 or so . Even the hydronics gets into this ~10 hour lagged ramp up to  overly hot, then another 10 hours to overly cool temps at about the same outdoor temps.
I sized all these systems to be able to handle -40 or a bit below when the house was poorly sealed and not well insulated.

Though it might be interesting to try out some of that coal it's my guess is that it would be extremely hard or impossible to make work here.
It would likely not be able to sustain a burn in the boiler at all, as it would heat all the concrete and the reserve heat tanks to max temp in no time, then shut down the draft long enough to kill it before the coal even got going really well.

We wind up using baseboard heaters a lot more than I like during these times.
Anything above 30f or so we can heat the place with just the waste heat from computers and tvs,  if we leave them on
Far cry from what we had when we first started working on the house.

So lessen learned, now I need to figure out a way to correct this issue someday, any suggestions are appreciated.

Ok its 6am and again I have not slept tonight because of sick kids..  :-\ so if I am rambling nonsense...

dang:
A long time ago we had a 25x40 pole barn on West Virginia property with one room insulated and dry-walled off up front. The heat was a lined barrel stove with a top load hatch. Gramps had a ton of Anthracite delivered put into woven-plastic feed sacks and stacked outside against the back of the building. Oh, yeah - there were small stacks of iron-like Black Locust wood from pruning & cutting down a few trees that were fence posts that had sprouted. Fast forward fifteen years and Gramps had departed us, the woven bags had departed from UV damage and the building was stuffed full of junk and other treasures. So suddenly I have a place to get out of town on long weekends - but it seemed like it was always winter when I visited there.

If you've ever broken up old furniture to burn when its zero°F indoors you'll know I should have gotten back into my car and runaway just as fast as my feet would carry me. But no, I'm burning cardboard and cheap discarded footstools and broken straight back chairs to try and get the frozen Black Locust to burn. Then I discovered the coal - using a digging bar to dislodge pieces frozen into the turf and mine the orange and grapefruit size pieces heaped up and cemented in with layers of snow.

Did you know the cans of spray-foam have a special steel top that will flex outward as a pressure relief when it expands from heating?  Well - when it does the plastic top is flung off at 200mph and will merrily ricochet around the room like a homicidal squirrel to warn you stored it in the wrong place. And that circline ceiling fluorescent fixtures have a 135°F clicks-off safety thermostat built in that shuts down the light to tell you the coal-fire has successfully gone Chernobyl? I don't know how many gallons of water I boiled off trying to get a token amount of humidity in the air - coal will heat the room air to two or 3% relative humidity and scorch sinuses and lungs dry if you haven't built up a tolerance. Oh - and a couple of aluminum beverage cans tossed in a coal fire will immediately collapse and drain down into the ash bin to leave perfect Hershey's Kisses droplets of solid aluminum?  Anyhow, back to really small scale coal for heat.

The secret of using small amounts of coal is to use coal against itself - It is possible to get one piece of coal, one bed the size of a tangerine burning and then keep the surrounding ash bed undisturbed around it and just add one or two lumps every hour. Think of coal as slow-motion black powder fireworks, get too much going and you'll not want to be anywhere near it. A stove pipe glowing cherry red is not healthful for children or any living thing.

The good hot fire to begin with is vital, but the key is coal chips and flakes about the size of corn kernels & ground corn layered - laid up in cardboard or paper that will turn to ash and keep the coal from falling through, and have acorn size lumps alongside so when the dust - flour - meal size flakes burn their heat goes to starting the larger lumps. It’s important not to throw in ten's of hunks of coal in hopes one will get started soon else then they all get going and you'll see things happening like I listed above. When you open up the firebox and see & smell the coal burning gently add in one or two larger pieces and some more wood kindling in that one spot & nurse the fire into changing over from wood to coal.

Anyhow - all this was done in a stove made to burn both wood and coal - well lined and a shaker grate and ash box that seals up fairly tight (very important to be able to STOP the draft)...  I’ve been collecting plates of metal alloys that laugh at oxy-acetylene torches (surplussed from silicon chip foundries) to try and make a micro-sized wood/coal stove to be supplemental heat in a forty-year-old Airstream trailer I am rebuilding as a hobby to hopefully use as home base when I homestead a chunk of really rural land. Just know that trying coal just once in a stove not designed to handle it will ruin the stove and possibly burn through and set the house on fire.

ChrisOlson:

--- Quote from: dang on January 18, 2012, 10:20:55 am ---A stove pipe glowing cherry red is not healthful for children or any living thing.

--- End quote ---

That's what I use for the visual temp indicator on the chimney - when the pipe goes from dull red to bright red the chimney is at critical temperature and it's time to shut the air off and let it cool down.

Our furnace has a built-in humidifier in it.  It goes thru about 5-6 gallons of water per day in cold weather.  Humidity in the house in the winter makes the house more comfortable with a lot less fuel burned.  That's a tip that few people realize.

We use stove coal, which is about 3" diameter chunks so stays on top of the grates pretty good.  You need special grates to burn acorn, pea or rice coal, and that stuff is better suited to auto-stoker furnaces.

Edit to add a tidbit: You never want to poke at an anthracite fire with the poker.  If you start poking at your coal bed to knock ash thru the grate, no matter how much draft you put on it in an attempt to keep the fire going after you destroy the ash bed, it will go out.  Furnaces designed for anthracite have either rocker or shaker grates to shake the fire down.  Over-shaking will do the same thing as poking at it - the fire will go out.  You shake the fire only enough to get some red coals to fall thru the grate and let air thru again, then leave full draft on while you add new coal to the bed.

The ash bed also helps insulate the heat of the coal fire from the grates.  You will damage your grates if you do manage to keep a coal fire going with no ash bed underneath.

You DEFINITELY need a furnace designed specifically for anthracite coal if you intend to burn the stuff.  Soft coal can be burned readily in most wood stoves, as it lights easily and doesn't get as hot.  But soft coal (or power plant coal, as some call it) burns smokey and sooty and I don't like the stuff.  You will melt or warp the firebox in a regular wood stove if you ever manage to get an anthracite fire going in the thing.  The anthracite is more expensive but I like how clean it burns.  We get it for about $225 a ton in plastic 40 lb sacks.
--
Chris

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