[Greenbuilding] firewood moisture content

nick pine nick at early.com
Mon Dec 19 06:32:21 PST 2011

>Here's a condensing pellet stove: 

I wonder what they cost. Will they be selling them in the US?

How about a condensing chimney, eg a conventional chimney heat exchanger 
http://www.amazon.com/Magic-Heat-Reclaimer-Wood-Stove/dp/B0000AXEXB with a 
fan that pushes room air through some small horizontal tubes in a 6 inch 
chimney pipe into 10 feet of 8 inch pipe surrounding 10 feet of 6 inch 
chimney pipe to make a condensing counterflow air-air heat exchanger? Some 
of the pressurized room air could enter the outdoor air inlet pipe of a 
conventional airtight woodstove for a bit of forced draft, with a room 
temperature thermostat to turn on the fan.

With A = 10Pi6"/12" = 16 ft^2 and Cmin = 10 Btu/h-F (10 cfm) and U = 2 
Btu/h-F-ft^2, NTU = AU/Cmin = Pi.  Cmax = 200 cfm makes Z = Cmin/Cmax = 0.05 
and E = (1-e^(-NTU(1-Z))/(1-Ze^(-NTU(1-Z)) = 0.95. Thi = 200 F and Tci = 70 
F makes Tho = 200 - 0.95(200-70) = 76 F.

Frank Tettemer <frank at livingsol.com>

>The other advantages of very dry wood are that the house receives more 
>BTU's per cord of wood. This results in less wood to bring in, and fewer 
>ashes to take out.

Water vapor makes ashes? :-)


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