[Cob] cob/earth oven also heating hot tub intake?

[Clint Popetz]

On Thu, Dec 30, 2004 at 11:28:13AM -0800, Tys Sniffen wrote:
 
> I would like to build a cob baking oven and run copper piping through it,
> probably in the middle of the 'fire box' area (so it'd look like a rack in
> the middle of the oven) and this copper pipe would have water flowing
> through it that would be attached to the intake/outtake of a hot tub. I'm
> sure most of you know about wood fired hot tubs with the stove as a separate
> unit (not a submersible).   The questions arise:
> 
> 1. Could the cob oven handle the temperature differences possibly created by
> the water flowing through it?

The cob could, but not the water.  The water in the pipes, if the
pipes are in the middle of a fire (or even close to it), will boil
pretty quickly, even if you are pumping it pretty fast.  Then you'll
have a massive expansion inside your pipes, and it will explode
wherever the pipes are weak (joints, seals, and valves.)  I'd run the
piping through cob that is close to the fire, but not in it.  That
would use the cob as a heat-exchanger, which is how on-demand
(tankless) water heaters work.  Incidently, when older on-demand hot
water heaters without safety mechanisms eventually die, they usually
do it in quite a spectacular fashion, exploding pipes throughout a
house, which of course sucks much worse than exploding pipes in a cob
oven :)

			-Clint