Inefficiency of burning wet wood

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M1sterM

Member
Aug 21, 2008
150
The Frigid North
I have a couple questions, and before I Google it, I thought I'd ask all you experts. A recurring theme on many of these threads is the issue of wood moisture content. 1) What are the percentages measuring, is it moisture content by weight or by volume?

2) We know how many BTU's there are per pound of wood, and even per different species of wood. However, if the average moisture content of the sticks are averaging, say, 25%, how many BTU's are you truly getting out of the wood, vs. transporting the moisture up the chimney? Obviously, you need to know the answer to #1 before you do the calculation. If someone answer's #1 for me, I can do some example calculations for #2, but anyone else, feel free.
 
1)It's by weight. We typically use weight of water/total weight of wood + moisture.

2) you first need to multiply the mass of water in the wood x rise in temp to ignition x heat capacity of water (1 cal/g C).
Then add the product of the # moles water x molar enthalpy of vaporization.
Then add any additional heating of the gas (vapor heat capacity x g x temp change).
Convert to "per pound" and subtract from BTU/pound of wood (which is normally tabulated at something like 20% moisture- so only do the heat calc for the water amount OVER 20% mc in the wood).
 
By the way- this does NOT account for inefficiency of burning either! If you get a smokey fire with wet wood- which ya do- then that means not all of the energy is being released (see wood gas thread) as particles are unburnt. You would also need to know the inefficiency of the process to do this calculation properly- it's not that all of the heat is being produced and some is wasted on boiling water- some heat is left on that table in the form of smoke!
 
Adios Pantalones said:
By the way- this does NOT account for inefficiency of burning either! If you get a smokey fire with wet wood- which ya do- then that means not all of the energy is being released (see wood gas thread) as particles are unburnt. You would also need to know the inefficiency of the process to do this calculation properly- it's not that all of the heat is being produced and some is wasted on boiling water- some heat is left on that table in the form of smoke!

Wow! Just think how smart A.P. would have been if they had not kicked him out of school for drawing cartoons!
 
Wow! Just think how smart A.P. would have been if they had not kicked him out of school for drawing cartoons!

Yes that was a very educated answer. Im guessing AP is a chemist or an engineer of some sort by profession?
 
ScottF said:
Wow! Just think how smart A.P. would have been if they had not kicked him out of school for drawing cartoons!

Yes that was a very educated answer. Im guessing AP is a chemist or an engineer of some sort by profession?

Naaa- he just stayed in a Holiday Inn Express last night. :)
 
Jags said:
ScottF said:
Wow! Just think how smart A.P. would have been if they had not kicked him out of school for drawing cartoons!

Yes that was a very educated answer. Im guessing AP is a chemist or an engineer of some sort by profession?

Naaa- he just stayed in a Holiday Inn Express last night. :)

Nah, he just got his paint brush stuck to the pallet and decided to become a rocket scientist
 
Elsewhere AP has posted he is an analytical chemist. By his first post in this thread you'd think he's still trying to prove it!! grin LOL
 
There is NO efficiency in burning non-seasoned wood with a moisture content more than 25%--PERIOD!!


Specially with a newer epa certified stove or insert. just equals= smoke and more smoke and very little heat.
 
sonnyinbc said:
There is NO efficiency in burning non-seasoned wood with a moisture content less than 25%--PERIOD!!

Say what, eh?
 
JPapiPE said:
Jags said:
ScottF said:
Wow! Just think how smart A.P. would have been if they had not kicked him out of school for drawing cartoons!

Yes that was a very educated answer. Im guessing AP is a chemist or an engineer of some sort by profession?

Naaa- he just stayed in a Holiday Inn Express last night. :)

Nah, he just got his paint brush stuck to the pallet and decided to become a rocket scientist

Remind me never to get into a war of wits with a Potter :cheese:
 
Remind me never to get into a war of wits with a Potter

You are a smart man.
 
BrotherBart said:
sonnyinbc said:
There is NO efficiency in burning non-seasoned wood with a moisture content less than 25%--PERIOD!!

Say what, eh?

Alright , then I mean greater than 25%. :red:
 
Can u say that in laymans term? Do I divide by 6 carry the 4, HUH? :roll:
 
Moles degrees celcius per kilocalorie squared times the velocity of light times the gravity gradient g divided by the levity factor k...

Gee, I didn't know they had a mole problem in that area.
I'd hire an exterminator pronto.
 
A pound of water requires 1 BTU to raise its temperature 1 degree F...until it gets to its boiling (or saturation) point, which depends on the pressure it's under. Since we don't run our woodstoves pressurized, we're normally talking in the expected range of atmospheric pressures spanning our elevations...not a great deal of difference so far as water's concerned. Let's just say we're at sea level and normal atmospheric pressure, then the saturation (boiling) temperature is 212 F. We've expended 1 BTU per degree of temperature change to get the pound of water in our wood up to 212 F. Now, in order to turn that pound of water into steam at 212 F, we have to pump in the latent heat of vaporization, which is roughly 1000 BTU's, if I recall correctly, something in that magnitude, anyway. So, we've burned a bunch of wood to heat a bunch of water, then burned a bunch more wood to turn the hot water into steam, and now all that steam is going to go up our stovepipes, carrying all our heat with it, just itchin' to lose its latent heat and condense back into a liquid, depositing all sorts of nasty things with it (what we call creosote). Water...can't live with it, can't live without it. Water in beer = good. Water in firewood = bad. Rick
 
I KNOW where you learned all that from. Most of that came straight out of a Navy boiler operating book!
 
This is gonna be good.

:lol:
 
Oh no, I've been outed! :ahhh: 30+ years in uniform, propulsion engineer all the way, and 3 degrees in Mechanical Engineering, and that's all I can remember anymore. And that gave me a headache. %-P Rick
 
And I've named my ship's wheel Eileen. :lol: Rick
 
Aww, how sweet :red:

Wait, I feel hands upon my throat :snake:

:lol:

I got a load of firewood last year in February, the wood dude was away on vacation. His assistant pulled from the front of the pile, making deliveries to customers with freshly split wood, instead of the seasoned stuff out on the lower back 40. It was a PITA to get dry. John made it right when he got back by bringing 1/2 a load of very seasoned... atleast I was able to keep cranking.

The 1/2 cord that's left of it is standing at the ready, all nice & dried, ready to do it's service, in the line of duty this winter :coolsmile:

I heart my firewood guy like whoa
pimp.gif
 
Doing The Dixie Eyed Hustle said:
Aww, how sweet :red:

Wait, I feel hands upon my throat :snake:

Don't worry, I won't steer you wrong. %-P Rick
 
Don’t worry, I won’t steer you wrong. Rick

Yeah, but what about Elsie?

250px-Elsie00.png


"And all I need is a tall ship, and a star to steer her by." John Masefield
 
She's a cow, you need a steer.
 
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