[Greenbuilding] heating water with wood stove - heat transfer/efficiency calculations?

Corwyn corwyn at midcoast.com
Wed Nov 9 10:02:26 PST 2011

On 11/9/2011 12:14 PM, Reuben Deumling wrote:
> Do any of you know a source for info on the following question?
> * design of simple wood-fired DHW calls for a coil of copper tubing
> either wrapped around the stove pipe or configured into a plate that
> would be attached to the outside of the firebox thermo-siphoning to a 10
> or 20 gallon storage tank in the attic. That tank of course would be
> plumbed into the household water system. The question is if there are
> basic calculations that would allow someone to know what sort of heat
> transfer rate he could expect?
> I.e., 20 lbs hardwood/160,000 BTU burned yields XY deg F increase in 10
> gallons of water.

20 lbs of wood @ 8,000 BTUs per pound = 160,000 BTUs.
times efficiency of the system (e.g. 60%) = 96,000 BTUs.
divided by 10 gallons of water * 8.3 lbs per gallon = 1,156 degrees F rise.

Alternatively, 96,000 BTUs divided by (say) 60 degree temperature rise = 
1,600 gallons of water

Thank You Kindly,


Topher Belknap
Green Fret Consulting
Kermit didn't know the half of it...
topher at greenfret.com
(207) 882-7652

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