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

[Reuben Deumling]

Frank,



Thanks so much for those great examples. I really appreciate your insights
here, especially on the custom SS stove pipe water jacket. Very cool
project—tempting to try a fully instrumented version.

A couple of questions.

 (1) when you say closed loop are we talking a storage tank with a coil
inside?

(2) since ten gallons of hot water would be plenty for each of the
households I have in mind here, I’m tempted to think that any temperature
rise achieved would be (roughly) 4x as quick/take ¼ as much wood to achieve
with a 10 gal tank vs your 40 gallons. Does that sound reasonable?

(3) On the Stanley cook stove, they do make a water jacket—or rather two
different sized ones for that stove, which is installed at the back (and
sides) of the firebox. My mother’s Stanley cook stove came with the larger
water jacket factory installed, and she loved how much hot water it
produced—too much really. When the water jacket sprang a leak (almost
certainly because we foolishly fired the stove for 18 years with no water
in the jacket) we tried to have it welded, and when that didn’t work we
went with the Lehman’s-supplied much smaller SS water jacket Waterford
sells for this stove. This one has much less heat transfer area and
consequently doesn’t make hot water as quickly. A compounding problem in
her situation is that the storage tank is 80 gallons(!) because that was
the only tank the solar installed could find with an internal coil…..



But overall I’m in agreement with you and Corwyn that with a short daily
burn cycle in a wood stove this DHW effort may not be well matched to the
fuel input. Which leaves me wondering if the smartest thing would be to use
the woodstove as a preheater and top things off with a tunable propane (or
biogas if I can source any) pilot light in the winter, and use a coil of
black hose inside a glass box on the roof for the summer hot water?
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