Musings on BTU Potential of Wood Vs. Coal in the Same Stove

davidmcbeth3 wrote:At least he has a sense of humor...^^

Yes funny.. What's funnier? It has over 33,000 views!!

Here is a chart I found on densities of wood and coal.
Based on grams per cubic centimeter.

wood (cherry) 0.43
wood (walnut) 0.59
wood (southern pine) 0.65
wood (sugar maple) 0.69
wood (birch) 0.71
wood (mahogany) 0.71
wood (oak) 0.85
ice 0.93
water 1.0
anthracite coal 1.55

Most people that use wood, I would assume use a hard wood similar to the last few that are in that list. Lets say a round about average density is .75 grams per cu cm. There is about 454 grams in a pound. Wood being around 7000 BTUs per pound would have 15.4 BTUs per gram times it's density (.75 g/cm3) = 11.56 BTUs per cubic centimeter of volume. 7000 BTUs per pound is actually a very modest figure. Here is more information on how ridiculous the BTU value of wood can be..

http://mb-soft.com/juca/print/311.html

Coal has roughly 12500 BTUs per pound. Break that into grams and get 27.5 BTUs per gram. Multiplied by its density (1.55 g per cm3) and you have 42.7 BTUs per cubic centimeter of volume.

Ok so if I did all this right , we can see that for its volume (the space it occupies), coal has about 4 times the heating potential that wood does. Keep in mind that in a pile of wood there is several times more air space between the peices than in a pile of coal. A face cord is about 43 cu ft at 8 million BTUs. (full cord 128 cu ft) Coal per ton about 25 million BTUs at only 33 cu ft per ton. So 3 face cords (1 full cord) ~ a ton of coal.

On a cold day I used about 100 pounds of coal and tended my furnace twice.
100 pounds X 12,500 is 1,250,000 BTUs for that day. It would take 178.5 pounds of wood to get the same BTUs and once the lower efficiency of wood burning is factored in (I'll be nice to the wood and figure 25% drop for simplicity), it would be well nearly 225 pounds of wood to do the same heating job. Lets be fair to the wood and acknowledge that there is more room in the fire box for wood (since it can be stacked over the bricks) I should be able to get half the heat potential than that of coal into the furnace. (twice as much wood as coal volume wise, but air space between the wood pieces is not figured in YET) At a factor of a quarter per volume of coal but able to load twice the volume, I would need to load the furnace at least 4 times that day with wood. That frequency increases to 5 times once efficiency is again factored in. Factor in again the bigger spaces between the wood peices and now we are up to 6 times to feed the furnace that day..

Furthermore, I would need 18 face cords of wood to get the same heat value as my 6 tons of coal. Oh wait, gotta factor in that efficiency again.. Make that closer to 23 face cords. At 4x8x16 in I would need a bin that is a minimum of 16 x 16 feet and 4 feet high. Thats nearly my whole basement.

To sweeten the deal, my coal bill is $1410 done and poured in the basement. Tend once a day, twice a day for two months. Wood bill would be over $1600 plus 4-5-6 times a day tending and angry wife (since she would be doing some loading, that right there is a deal breaker), chimney fires, no room left in the basement after I lugged it all in not to mention the ecosystem it would develop (termites, potato bugs, bores.. whatever) and the home it would make for rodents. Not to mention my cat wouldn't be able to get to them.

Shwew.... Glad I got that outta my system..

Disclaimer - figures used are approximations for demonstrational purpose..

That's it. But it won't fit in a nutshell!

what 3 cords look like....

https://www.hearth.com/talk/threads/wood-estimation.143499/

18 cords would be 6 times that .... so ... do people actually burn 18 cords / season?

6 tons of coal, sure...I burned 7 this year.

I guess one could go to the hearth website and see how much they burn over the season....maybe better than any calculations and no experimentation is needed after all...as it has already been done and reported (like we note how many tons/season we used),

Lightning wrote: Not to mention my cat wouldn't be able to get to them.
.

My cat today, and I just noticed this today...

I let my cat outside .. he hangs around the perimeter of the house trying to catch humming birds in vain. He'll ask to be let back into the house every so often.

So today, I let him out, he comes back to the door in about 1/2 hr ... I let him in. He's in for about 3 min. and wants to go back out. OK, out he goes. I noticed that he went to the toilet (as I trained him to do -- no litter box).

So did the cat come into the house just to use the toilet? ie we will not do his business outside?

maybe maybe ... further observations will be performed ....

stupid cat

When I was a kid, we had a cat that used the toilet. Pretty funny, I don't really know how he learned that trick other than by watching us lol.

I went over to hearth.com for a minute. I realize I need to get out a little more often and maybe I'm a bit of a coal snob but... sure is weird seeing people talk about wood like we talk about coal. I think I'll stay over here thanks.

Lightning wrote: I went over to hearth.com for a minute. I realize I need to get out a little more often and maybe I'm a bit of a coal snob but... sure is weird seeing people talk about wood like we talk about coal. I think I'll stay over here thanks.

You are definitely a snob! I go over to hearth.com all the time to see what folks over there are doing. I listen to them talk about their chain saws, axes, and all the things they need to get their wood in... and I think to myself how one day, many years ago now, I did all that just like them... And I say to myself, coal is sooooo much easier.... Plus I get to use a really cool old stove and it runs great on coal. Pretty much sucks on wood (compared to a good modern wood stove), but runs great on coal.... I don't miss the bugs, the bark, the dirt, the weight, the tending, the lost fires. I do like the smell of wood burning... I enjoy walking the neighborhood and smelling the wood stoves running. I almost miss it... And I reminisce about when I also thought wood was great.....

It's called evolution...

dj

We have the coal forum, wood folks have the hearth forum. Want to see snob? Go to the diamondstove.org forum ... people who burn diamonds for heat, they are the snobs.

Lightning wrote:Here is a chart I found on densities of wood and coal.
Based on grams per cubic centimeter.

wood (cherry) 0.43
wood (walnut) 0.59
wood (southern pine) 0.65
wood (sugar maple) 0.69
wood (birch) 0.71
wood (mahogany) 0.71
wood (oak) 0.85
ice 0.93
water 1.0
anthracite coal 1.55

Most people that use wood, I would assume use a hard wood similar to the last few that are in that list. Lets say a round about average density is .75 grams per cu cm. There is about 454 grams in a pound. Wood being around 7000 BTUs per pound would have 15.4 BTUs per gram times it's density (.75 g/cm3) = 11.56 BTUs per cubic centimeter of volume. 7000 BTUs per pound is actually a very modest figure. Here is more information on how ridiculous the BTU value of wood can be..

http://mb-soft.com/juca/print/311.html

Coal has roughly 12500 BTUs per pound. Break that into grams and get 27.5 BTUs per gram. Multiplied by its density (1.55 g per cm3) and you have 42.7 BTUs per cubic centimeter of volume.

Ok so if I did all this right , we can see that for its volume (the space it occupies), coal has about 4 times the heating potential that wood does. Keep in mind that in a pile of wood there is several times more air space between the peices than in a pile of coal. A face cord is about 43 cu ft at 8 million BTUs. (full cord 128 cu ft) Coal per ton about 25 million BTUs at only 33 cu ft per ton. So 3 face cords (1 full cord) ~ a ton of coal.

On a cold day I used about 100 pounds of coal and tended my furnace twice.
100 pounds X 12,500 is 1,250,000 BTUs for that day. It would take 178.5 pounds of wood to get the same BTUs and once the lower efficiency of wood burning is factored in (I'll be nice to the wood and figure 25% drop for simplicity), it would be well nearly 225 pounds of wood to do the same heating job. Lets be fair to the wood and acknowledge that there is more room in the fire box for wood (since it can be stacked over the bricks) I should be able to get half the heat potential than that of coal into the furnace. (twice as much wood as coal volume wise, but air space between the wood pieces is not figured in YET) At a factor of a quarter per volume of coal but able to load twice the volume, I would need to load the furnace at least 4 times that day with wood. That frequency increases to 5 times once efficiency is again factored in. Factor in again the bigger spaces between the wood peices and now we are up to 6 times to feed the furnace that day..

Furthermore, I would need 18 face cords of wood to get the same heat value as my 6 tons of coal. Oh wait, gotta factor in that efficiency again.. Make that closer to 23 face cords. At 4x8x16 in I would need a bin that is a minimum of 16 x 16 feet and 4 feet high. Thats nearly my whole basement.

To sweeten the deal, my coal bill is $1410 done and poured in the basement. Tend once a day, twice a day for two months. Wood bill would be over $1600 plus 4-5-6 times a day tending and angry wife (since she would be doing some loading, that right there is a deal breaker), chimney fires, no room left in the basement after I lugged it all in not to mention the ecosystem it would develop (termites, potato bugs, bores.. whatever) and the home it would make for rodents. Not to mention my cat wouldn't be able to get to them.

Shwew.... Glad I got that outta my system..

Disclaimer - figures used are approximations for demonstrational purpose..

i love this post so much I just had to quote it.

what a great reality check and I like many others went thru the very same struggle of doing it over and over yr. after yr. when I was QUITE a bit younger, "cause it's FREE heat man".

Lightning comments of using 100#'s of coal on a cold day and tending twice. I have to admit in recent seasons, I have had days when it was just impossible to work outside. -20F with 25 mph winds affecting the shell of my house, i'm not even walking to the car. so i'm sitting around casually in shorts and a "T" in 72* room temp. and over 24 hrs. put 3 / 25# buckets of coal thru the stove and think i'm being TORTURED. man am I getting old.

I have to say before i'd do the wood thing ever again, i'd move to the coast, desalinate sea water, sell off the ammonia, electrolise the fresh water, direct vent the oxy. to atmosphere, burn the hydrogen for all domestic applications, condense and capture the recombinated water from the burning process for domestic use as well.

but long before that happens, i'll move over to Rev. Larry's area where they use coal for landscaping cause it's cheaper than gravel and if nec. live like a hermit cause of the limited income opportunities.

coal's IT for me brother.

What a fantastic idea! Split the water into hydrogen and oxygen with solar generated electricity. Then use the stored hydrogen for heating and condense the exhaust for pure drinking water. Sweet ... As a curious young teenager I used to split water with a DC transformer and ignite the hydrogen just to prove to my friends that it could be done. Oh what fun.. I'm sure that could have gotten dangerous had I pursued bigger and better things with it

right, the problems start when you try to get a system capable of producing usable amounts of hydrogen and storing it under pressure, any smaller than a service style "foot locker" . then you still need another system for space heating / cooking and condensing the exhaust vapor, another "foot locker".

not entirely "portable" by some standards but once your "refuge" has to be smaller than a mini van you will just be survival filtering water and burning sticks in a rocket stove, at best, anyway.