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DIY outhouse woodburning boiler, made from pipe?
QUESTION:A friend sent me an email about those "outhouse" woodburning boilers
that will heat your house, etc, and burn large chunks of wood pretty
slowly... doubtless you've seen them? Maybe you even own one.
Anyhow they're expensive... usually made from welded up plate,
sometimes cast, and sometimes a stainless alloy...
The idea is that you make a huge firebox, burn a large chunk of wood
very slowly and heat a large thermal mass of water which then is used
to transfer the heat to your abode. The firebox is often enclosed by
insulation (one outfit uses foam!) which I've heard can be sand (yes?)
and then put into a metal doghouse which stands some distance from
the home...
My thinking is that the idea is a good one, if you have wood and want
heat that doesn't require stoking up every 6-8 hours or less.
So I thought about how I would build one on the cheap, and decided
that some 3"-4" dia *pipe* about 5ft - 6ft long placed side by side to
the requisite width and with a manifold on each end would be a
modular way to create the "wet" part of the "boiler" without much
expense... then make 4 of them, place in a rectangular configuration
and jacket that with simple plate and angle (you could weld it) as
the outside of the "firebox" - mount up a front and back plate with
requisite doors/flue/in & out piping etc. That would be the guts.
Place that in a concrete block building with sand or whatever as
outer insulation/additional thermal mass and ur done... after you
go nuts with plumbing, circulators and pop off valves, thermostats
and that stuff.
I figure that by the time you get to the outer jacket the temp will
be rather moderate in this sort of setup...
NOW, here's the *metal* question... I know commercial boilers *are*
made with tubing in some cases (when they're not cast), I'm wondering
if lowly "black pipe" will suffice in this application? I'm thinking of
thermal stresses, not so much pressure. It should handle any pressure
that a non steam system will produce no prob. If the pipes die in
10 years, I don't care. (I'm figuring on making the thing modular and
fairly easy to replace...)
So, is there a pipe to avoid? Will this work? The fire will be directly on
the pipes, the pipes are filled with water/antifreeze. Is there an optimal
pipe (within $ reason)? What do the commercial boilers use?
Will this work?
ANSWER: Boilers use boiller tubeing. Its pretty well smooth and uniform in
finish. Normally a header plate is made with holes corresponding to
the tubes OD and a boiler tube expander is used to swell out thre
tubes in this header to make a water/firetight seal. Easy to replace a
tube if need be, well its not too bad to replace them anyhow. If you
buy boiler tube most plumbing supply places that sell the tube will
also loan you a tube expander as well I would think making a double
jacket out of steel plate with two headers to roll the tubes in, would
be a more simple approach.
Boiler tube is not all that much more $$ than run of the mill black
pipe is.
When I lived up north I did something like this but on a smaller scale
and used my fireplace as the heat source. I lined the fireplace with
sections of the low more modern modular cast iron baseboard heat,
including making a grate out of a nice thinline sectin of cast iron
radiator. I plumbed them all together and then ran this line to 4, 55
gal water heaters which were like a holding tank. I had cast iron
baseboard radiators in a few sections of my house and used a
circulating pump to circulate the hot water through this system. Other
than an over pressure device if water started to boil (was never a
problem really) it continuously circulated the hot water through
this system continually. It did a fair job of adding auxillary heat to
rooms in the house while I had a fire burning in the fireplace, which
was usually 24/7 during winter months. I had a pressure reducing
valve with auto fill set for a couple of pounds pressure to keep the
system topped off. I also had a air bladder type expansion tank in the
system.
Visit my website: http://www.frugalmachinist.com
Opinions expressed are those of my wifes,
I had no input whatsoever.
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