I know it all depends on the type of wood so lets just assume that I'm referring to a good hardwood like oak, hard maple or elm. Approximately how much does a cord (4'x4'x8') of split wood weigh? I would guess around 1500lbs. From all you experts out there, does this seem close?
Weight of wood
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Red oak, "seasoned," which I assume to mean about 20-25% MC, 3500 lbs per cord. Whether split or unsplit, logs or rounds, I don't know.
heaterman said:All wood weighs 2000# per ton.
Sorry, couldn't resist
yea but what is heavier, a pound of Oak or a pound of pine?
Biomass grower said:
I'm coming into this late, but the link above is pretty much definitive. I pick up 1/3 cord racks with my bucket loader, and it struggles if it's green wood. It's rated for 1400 pounds. I would guess that a full cord ranges from a ton and a half to two tons, maybe a bit more than that if it's green.
To put it in perspective, a cord of wood for me replaces 1000 pounds of fuel oil - about $600 worth at today's prices.
Thanks for the link. I was just trying to ballpark how many fullsized pickup loads I'd need for a winter compared to natural gas that I use now (heat and domestic water). I used an average of 500,000btu's per day this last winter during the rough 2- 3 months, although there seemed to be more of these months this year than last. Can't believe that my boiler was actually running and the end of May with overnight temps into the mid 40's.
Just looking at the chart though brings a question. I thought that wood had 8600btu's per pound? According to that chart it would be somwhere around 6400 btu's/lb. Maybe they are already figuring recoverable heat?
At any rate, a full size pickup of UN-split wood if it is heaped high up with ~8' logs is chunked, split and then stacked, it would be fairly close to one cord. If I used a good hardwood at 20 to 24 million btu's per cord (from chart) which is burnt at a 60% recoverable heat I would need about 2 cords or pickup loads a month during the worst of the winter and maybe 1 load a month for the other 3-4 months. This seems to be to good to be true. I guess we will find out whenever I get everything in place.
Just looking at the chart though brings a question. I thought that wood had 8600btu's per pound? According to that chart it would be somwhere around 6400 btu's/lb. Maybe they are already figuring recoverable heat?
At any rate, a full size pickup of UN-split wood if it is heaped high up with ~8' logs is chunked, split and then stacked, it would be fairly close to one cord. If I used a good hardwood at 20 to 24 million btu's per cord (from chart) which is burnt at a 60% recoverable heat I would need about 2 cords or pickup loads a month during the worst of the winter and maybe 1 load a month for the other 3-4 months. This seems to be to good to be true. I guess we will find out whenever I get everything in place.
'Recoverable heat' is the key phrase. Perhaps that should be 'theoretically recoverable heat'. First of all, the 8600 BTU/lb is for bone-dry wood. Unless you do kiln drying, fully seasoned wood is about 20% water by weight. That gets you down below 7000 BTU/lb. It takes energy to boil that water, so unless you have a condensing wood boiler, that energy is not available to you. A reasonable figure of merit is about 6700 BTU/lb recoverable heat energy.
Of course, wood boilers are not 100% efficient. The very best gasifiers are about 90% under unrealistic ideal conditions. A better working number would be around 70% for a very efficient indoor gasification boiler. At the other end of the spectrum, some OWBs have an overall system efficiency of less than 20%.
I have an EKO 25 in a fairly ideal installation. Depending on how I measure it, I get overall system efficiency somewhere between 55% and 70%. That means for every pound of actual wood (not water) that I burn, I deliver between 4700 and 6000 BTU into my house, hot tub, and hot water.
Of course, wood boilers are not 100% efficient. The very best gasifiers are about 90% under unrealistic ideal conditions. A better working number would be around 70% for a very efficient indoor gasification boiler. At the other end of the spectrum, some OWBs have an overall system efficiency of less than 20%.
I have an EKO 25 in a fairly ideal installation. Depending on how I measure it, I get overall system efficiency somewhere between 55% and 70%. That means for every pound of actual wood (not water) that I burn, I deliver between 4700 and 6000 BTU into my house, hot tub, and hot water.
Thanks. So that would be about right (if I had your system). Lets say 60% of 6700btu's/lb is recoverable therefore equaling 4020 btu's/lb of wood. If 500,000 btu's per day divided by 4020 btu/lb to give 125 lbs of dry wood per day. Multipkly by 30 days a month would give 3750 lbs of wood/month. From the chart that would be about 1 cord of hardwood during the cold months and 1/2 to 2/3 cord for the other 3 to 4 months. That seems even a little less that the previous calc but also assumes I have system efficiencies similar to nofossil. Well, I guess you all know what that means..... no fossil has another installation job this summer! When do you start?
Biomass grower said:
I used just over 4 cords each of the last two seasons to heat 3500 square feet, hot water, and a hot tub. YMMV.
Still waiting for an invitation to that Caribbean install.......
If I grill up some Jerk chicken breast and have my wife serve an assortment of tropical fruits in her bikini would that count? Oh, I suppose I could get some fresh fish flown in too. You just name your flavor.
Biomass grower said:
Now why would I want fruit served in your wife's bikini? That's a bit strange if you ask me.....
Seriously, if you saw my plumbing work you'd not be so quick to invite me. Eric was kind enough not to laugh, but I think it's fair to say that I can analyze and design much better than I can solder.
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