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re: outdoor woodstoves
3 dec 2005
jazzman enquired re:
>... the principles are wrt a "condensing" chimney, care to elaborate?
many things make water vapor when burned. it usually goes up a chimney in
vapor form, but condensing the vapor back to a liquid can add 5 (oil), 10
(natural gas), or 15% (wood) to the useful heat output of a pound of fuel.
water boils at 212 f, so condensation requires lower flue temps, which can
be achieved by removing more heat from a flue. a very long indoor bare flue
pipe is one way to this. some old new england churches have large potbelly
stoves in the back and very long gently-sloped flue pipes that run all
the way to the front over the pews before exiting near the ceiling.
the corrosive condensate needs a drain. it can move lots of heat through
small surfaces, eg 2000 vs 2 btu/h-f-ft^2. it may allow burning damper wood
cleanly, with a hotter firebox. a cooler chimney with less draw may need
a small combustion air fan blowing air into the stove (easy, but dangerous
if the flue pipe leaks), into the chimney (harder, requiring a high temp
blower), or sucking air out at the chimney top (still harder, but safer if
the chimney leaks.) the safety issues are less important outdoors, esp. if
heat moves indoors in the form of hot water. outdoor stoves with combustion
fans can have very short small diameter chimneys. the fan can also run
faster when more heat is required, eg when the water temp drops.
>regarding storing water indoors, drums aren't a problem as i have
>a source that will sell and deliver plastic water drums fairly
>inezpensively. i am not particularly worried about aesthetics so
>much as not wanting the pipes to freeze this winter.
seems to me that woodstoves are unreliable freeze protection,
compared to an electric space heater with a 40 f thermostat.
>the foil would probably go well with my afdb. :)
what's an afdb?
nick
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