Outdoor Wood Furnace Info
All-Purpose OWF Discussions => General Outdoor Furnace Discussion => Topic started by: jreimer on January 15, 2018, 09:01:28 AM
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I would like to switch to weight when talking about daily wood usage. I find it pretty useless to talk about 1/2 full, 1/3 full or completely full load when there are so many variables to log length, split sizes, stove sizes and wood types. If we all talk lbs. of wood per load or per day, we can compare apples to apples when talking about wood usage, efficiency and heat loads.
Right now I'm burning around 150 - 200 lbs. of wood every 24 hours split over 3 fills.
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Do you physically weigh each block or how are you finding an accurate daily weight?
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I have some big tubs that I have filled and weighed. Then I know approximately what I'm putting in for that species and log size going forward.
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jReimer
While you're at it, make sure you quote species and % water content, or it's meaningless data.
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Smithbr, that's the beauty of using weight as the measurement. It takes the species out of the equation and we don't have to worry about what species you're burning compared to what species I'm burning. 100 lbs. of spruce has the same btu's as 100 lbs. of oak, it's just much larger physically.
However, moisture content is still an important factor though. 100 lbs. of 40% spruce will have much fewer btu's than 100 lbs. of 20% oak.
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jreimer
Please quote a verifiable source that shows that 100 lbs. of spruce has the same btu's as 100 lbs. of oak, dried to the same MC. Are you saying it's absolutely invariant, or just that it's a second-order effect? I'll grant you, if you want to only dry for one season, you'll want to burn pine.
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jreimer
Please quote a verifiable source that shows that 100 lbs. of spruce has the same btu's as 100 lbs. of oak, dried to the same MC. Are you saying it's absolutely invariant, or just that it's a second-order effect? I'll grant you, if you want to only dry for one season, you'll want to burn pine.
All wood species have the same amount of btu's per pound at the same mc. The difference is density. A cord of oak weighs a lot more than a cord of pine.
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Yep
The MC matters for two reasons. One, if you're weighing water, it has no heat content to release in combustion, and secondly, it robs your combustion cycle of heat, because you have to vaporize it and send it up the stack as steam. So, what are we comparing? We have to quote pounds of wood, at a specific MC. Not everyone has a moisture meter. Telling me you're burning oak you cut last spring doesn't help, because
- did you split it immediately? How small? Is it piled in a mountain(surface gets rained on, center of stack sees no airflow), row-stacked in the open(better airflow, but gets rained on, so MC isn't consistent), in the open under a tarp(is the tarp preventing airflow), in the open under a waterproof roof, no walls(ideal, gets airflow, no rain), in an open shed that's surrounded by forest(poorer airflow, but pretty good drying), or in a closed shed (hasn't dried nearly as well, no airflow; could even be growing fungus).
So you see, it's pretty hard to have a standard unless we all have a moisture meter.
Re Species BTUs - source? "Grampa told me" won't do. I can't find it on the web (at least not in a useful tabular or graphic form, just a few species of softwood in Idaho which by the way vary quite a bit), but I'm not looking as hard as you should be, as you made the statement. I'm not being a PITA here, I'd like to see the data. I'm willing to say I'm wrong, but not just because you say so...
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jreimer
Please quote a verifiable source that shows that 100 lbs. of spruce has the same btu's as 100 lbs. of oak, dried to the same MC. Are you saying it's absolutely invariant, or just that it's a second-order effect? I'll grant you, if you want to only dry for one season, you'll want to burn pine.
You're correct that they're not absolutely perfectly equal, with resinous woods having slightly higher btu's per pound than non-resinous. Some of the lesser desired woods (softwoods) actually have slightly higher btu's per pound than hardwoods!
However, I feel they are close enough that our back-of-napkin calculations can disregard these differences as irrelevant compared to other fudge factors.
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Granted, it's likely down there below the error bar on a moisture meter used in uncontrolled conditions.
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While a good ideal and the reasoning holds water, not everybody has an easy way to weigh their wood.
I could, if I wanted to leave the tractor on vertical TMR plugged in 24/7, start it, back it out of the shed, lower the conveyor, place the wood on it, get a reading, take the wood off the conveyor, raise the conveyor, drive it in the shed, shut it off. Not worth the electric or wear and tear and a cold engine and hydraulic system.
I wished when my BIL quit racing stock cars I would have grabbed one of the old balance beam scales he used for setting it up.
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I didn't do anything fancy to know my approximate weights. Rubbermaid storage tubs from Walmart and the bathroom scale (needless to say the wife was not impressed). Measured how many tubs worth of wood I was using, weighed a few tubs and there was my approximation. You don't have to check every time. After a few days and different weather scenarios you can judge how much wood you're using and how much your logs and splits weigh. If you're unsure or if you change species, just fill the tubs and weigh them again before throwing that wood into the boiler.
Sure it won't come close to passing any engineering test, but with a bit of due diligence in measuring I think it's still more accurate than saying "I use 1/2 a firebox full a day every 8-14 hours".
I know it's still not perfect but it could help standardize troubleshooting when we're trying to diagnose problems over the web.
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Like I said, reasoning is solid and your right, taking a guess on how much your using can get sketchy.
My father AKA The Chimney Fire King, still can’t believe we actually stack the wood in totes instead of just leaving it in a pile. Probably give him another stroke if he found out we were weighing it too. :P
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Sounds interesting, I am in, gotta get the stuff first, am NOT taking the wife's bathroom scale. :bag:
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Just for sh?ts and giggles, is there anyone who uses strictly softwood on here?
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I am right now. Just spruce and spruce structured cutoffs from a pallet factory in town. I have some ash for when I need >10 hour burns if needed.
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Like I said, reasoning is solid and your right, taking a guess on how much your using can get sketchy.
My father AKA The Chimney Fire King, still can’t believe we actually stack the wood in totes instead of just leaving it in a pile. Probably give him another stroke if he found out we were weighing it too. :P
:post: Very funny too....LOL
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I'm just about at 50% though my 6 ton bulk bin! :thumbup:
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I didn't do anything fancy to know my approximate weights. Rubbermaid storage tubs from Walmart and the bathroom scale (needless to say the wife was not impressed). Measured how many tubs worth of wood I was using, weighed a few tubs and there was my approximation. You don't have to check every time. After a few days and different weather scenarios you can judge how much wood you're using and how much your logs and splits weigh. If you're unsure or if you change species, just fill the tubs and weigh them again before throwing that wood into the boiler.
Sure it won't come close to passing any engineering test, but with a bit of due diligence in measuring I think it's still more accurate than saying "I use 1/2 a firebox full a day every 8-14 hours".
I know it's still not perfect but it could help standardize troubleshooting when we're trying to diagnose problems over the web.
I like your thinking. When I first commissioned my system in 2010, I weighed the wood, measured boiler temps and monitored the time to try to get a sense of the overall efficiency. To weigh the wood, I put blocks in a heavy shopping bag and used a luggage scale. I soon learned, that in my case, an average sized block of seasoned wood was 14 lbs. There is no need to over analyze and over think all this. Keep it simple and there is a much greater chance of continuing the measure and monitor process.
There is some debate as to how much BTU's are available in a pound of wood. We have to take into account the water in the wood, also the hydrogen that is combined within the wood's hydro carbon structure as it also combines with oxygen to form water. This process creates heat, but stack temp needs to be kept high enough so this water does not condense. So some will say 6800 BTU/lb, and I have seen estimates as low as 6050 BTU/lb. You are right in that species is basically irrelevant.
Some fun bedtime reading;
http://mha-net.org/docs/v8n2/docs/WDBASICS.pdf
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Thanks BoilerHouse. That's a great document that I've read before.
I've measured my BTU recovery efficiency in more ways than I can count. I have used the 6000-6500 BTU per pound of wood (20% moisture, 100% heat recovery efficiency) calculation before. I've discovered that a very conservative calculation is 4500+ BTU per pound of actual heat to my house. I'm always hitting at least this efficiency or better. That would put my stove at around 75% efficiency, just like the EPA sticker on the unit says.
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I'm burning oak debarked slabs. I know -21f takes 400 lbs for 12 hours. I have burned 10 bundles 2100 lbs a bundle started season with 42,000 lbs of slabs. There dry to 15-25% heating 6600sqft
I call them Atomic slabs. Serious heat in them . Only need to make 2 cuts in each bundle.
Heat550
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Wow, 800 lbs. in 24 hours! That's 5,200,000 raw BTU's. Good thing you're getting your wood delivered and not cutting it yourself.
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Slabs are a funny burn they get so dam hot . Im only putting in about 200 lbs at a time and getting 8 hours below 0f
but -21f stepped that up even more .. There oak so last alot longer then soft wood . But ya its a different style of burning .
with math I can fit about 600 lbs slabs in the boiler but Im not going to because they all burn at once . and Im not going to put the flippers to the test maybe on a day without wind I can try more at a time .. But its working I don't need to push harder .Im still in the testing faze .. at below 0f as I put the slabs in they start on fire just when they get by the door . Its pretty crazy . I know Im getting my 6388 btus per pound LOL
Heat550
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Jeepers, that seems like a LOT of slabs. Guess I've never weighed my wood but I would estimate 75-150 lbs per loading, twice a day depending on temp. What does your 800 lbs a day come out to be in a full season, cord-wise Heat550? Maybe I'm way off. Also, is there any sort of draft damper plate to adjust air input on your stove? If you're blowing through the wood by loading it for 12 hours, I wonder if you could choke the air down a little bit to even out the burn some
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Yes Im playing with drafts still..putting pan like in front of draft fans to slow it down .. each bundle is 2100 pounds below 0f it goes fast. Above 0f it hardly taking any . So if you figure in warm days and cold days I average about bundle a week. I got 20 bundles witch works to little over 11 cord so far I burned 12 bundles and have 8 left . I think I will make it thru the winter long as we don't have weeks of subzero. 20 bundles 42,000 lbs it's the same as $3500 bucks of LP I figure in stove and furnace efficiencies. I'm heating 2 good size houses and shop and garage. 6600sqft
Heat550
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slabs in my Heatmor were insane. so hot, that's the only time that I burnt my beard...lol
I found what worked best in my Heatmor 400 was 4ft rounds of oak about 4-6" in diameter. I would stack about 3/4 firebox and even in negative temps, she would pur right along. I also liked to mix large 4ft rounds of softwoods like pine, maple and even poplar with the oak slabwood. that seemed to be a good combination.
now with my g200 its been a crazy transition. I am using WAY LESS wood and heating more square feet. Im not sure on the total poundage but on a typical day I would say I load 12-14, 20-22" long, 4-6" splits twice per day heating 4400 sqft. sometimes more, sometimes less depending on the weather
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If I can burn 11 cord of oak slabs in a winter it's a record because that will be the least amount of wood I put in boiler over a winter.
Least of chunk oak was 12 cord and that was a mild winter. 6600 sqft is alot of space to heat it all got out of hand lol . If I do some better insulation install and tight up air leaks I might get to point I'm at 10 cord. But that might be a dream because the one house is held at 76f it's 28x48 it takes alot of BTUs. lol
Heat550
Yes oak slabs are about dialing down the draft fans. They burn hot !!
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slabs in my Heatmor were insane. so hot, that's the only time that I burnt my beard...lol
I found what worked best in my Heatmor 400 was 4ft rounds of oak about 4-6" in diameter. I would stack about 3/4 firebox and even in negative temps, she would pur right along. I also liked to mix large 4ft rounds of softwoods like pine, maple and even poplar with the oak slabwood. that seemed to be a good combination.
now with my g200 its been a crazy transition. I am using WAY LESS wood and heating more square feet. Im not sure on the total poundage but on a typical day I would say I load 12-14, 20-22" long, 4-6" splits twice per day heating 4400 sqft. sometimes more, sometimes less depending on the weather
Heatmor slab burning my old 200 had pan on the fan to adjust air flow the new 2015 400 didn't come with pans on the fans. So I just put pans on the 400 for slab burning . Pretty simple . Takes the thunder out of the Dragons . And I left the rain cap on . Guys that say you can't burn dry wood is wrong .. you just slow down the draft to get longer burns .. just think they had this in 1994 they knew..
Heat550
That's all the draft I need to burn slabs this is the one goes under the grate.. I'm going get one on the back fan also.