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Author Topic: Wood usage comparisons  (Read 7671 times)

jreimer

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Wood usage comparisons
« on: January 15, 2018, 09:01:28 AM »

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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Shindaiwa 488
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wreckit87

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Re: Wood usage comparisons
« Reply #1 on: January 15, 2018, 09:24:01 AM »

Do you physically weigh each block or how are you finding an accurate daily weight?
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jreimer

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Re: Wood usage comparisons
« Reply #2 on: January 15, 2018, 09:30:31 AM »

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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Shindaiwa 488
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smithbr

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Re: Wood usage comparisons
« Reply #3 on: January 15, 2018, 09:34:58 AM »

jReimer
While you're at it, make sure you quote species and % water content, or it's meaningless data.
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jreimer

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Re: Wood usage comparisons
« Reply #4 on: January 15, 2018, 09:45:07 AM »

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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smithbr

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Re: Wood usage comparisons
« Reply #5 on: January 15, 2018, 10:05:41 AM »

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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woodman

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Re: Wood usage comparisons
« Reply #6 on: January 15, 2018, 10:15:08 AM »

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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smithbr

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Re: Wood usage comparisons
« Reply #7 on: January 15, 2018, 10:29:20 AM »

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

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Re: Wood usage comparisons
« Reply #8 on: January 15, 2018, 10:41:03 AM »

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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Shindaiwa 488
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smithbr

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Re: Wood usage comparisons
« Reply #9 on: January 15, 2018, 10:55:31 AM »

Granted, it's likely down there below the error bar on a moisture meter used in uncontrolled conditions.
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mlappin

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Re: Wood usage comparisons
« Reply #10 on: January 15, 2018, 11:37:39 AM »

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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jreimer

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Re: Wood usage comparisons
« Reply #11 on: January 15, 2018, 12:07:44 PM »

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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Shindaiwa 488
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mlappin

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Re: Wood usage comparisons
« Reply #12 on: January 15, 2018, 12:38:49 PM »

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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coolidge

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Re: Wood usage comparisons
« Reply #13 on: January 15, 2018, 12:55:59 PM »

Sounds interesting, I am in, gotta get the stuff first, am NOT taking the wife's bathroom scale. :bag:
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coolidge

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Re: Wood usage comparisons
« Reply #14 on: January 15, 2018, 01:20:09 PM »

Just for sh?ts and giggles, is there anyone who uses strictly softwood on here?
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