[Greenbuilding] firewood moisture content - a question for Norbert perhaps

Corwyn corwyn at midcoast.com
Mon Dec 12 05:51:07 PST 2011


On 12/11/2011 9:56 PM, Reuben Deumling wrote:
> Let us say I have a cord of firewood that registers 15% moisture
> content, and a cord that registers 20% moisture, and one that registers
> 25%.
>
> I burn the 15% cord and get XY BTUs/lb out of it.
> I burn the 20% cord and almost certainly get fewer BTU/lb out of it, but
> how much less usable heat?
> And the same for the 25% cord?
>
> Put more succinctly, what is the penalty for having firewood that is not
> quite dry?

The energy you get from the chemical conversion of cellulose is going to 
remain the same (approx 8000 BTU per pound).  The difference is the 
amount of water which is going to need to be vaporized (at 970 BTU per 
pound).  Percent moisture is by dry weight (in other words, 15% moisture 
is 1 pound of wood + 0.15 pounds of water) so an extra 5% moisture 
content will thus decrease the useable heat output by about 0.6%.

Thank You Kindly,

Corwyn

-- 
Topher Belknap
Green Fret Consulting
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