Wood stove water heating options

 

Hi,

I know this topic has been discussed occasionally, but I would like to
bring it up again in a little more detail. I would like to heat water
by using a wood stove. Specifically, I will be heating a hot tub. Most
systems I've read about online are just to supplement a domestic hot
water heater, which requires considerably less BTU than my application.
I'd like to have the cabability of heating 600 gallons of water from 50
F to 104 F in 4-6 hours.

In the future, I might use the same system for hydronic baseboard
heating (to supplement my existing living-space heating). But the hot
tub is the main priority.

The systems I've read about are:

1- Entire firebox immersed in water
(Snorkel / Scuba / Chofu stoves)

2- Heat exchanger inside flue
(coil of piping suspended in flue)

3- Heat exchanger outside flue
(coil of piping wrapped around outside)

4- Flue passing through water
(stove pipe just passes through a container of water; one-pass or
two-pass versions exist)

5- Heat exchanger inside fire box
(radiator-type piping mounted to the top of the fire box)

6- Heat exchanger outside fire box
(radiator-type piping, possibly enclosed in a box filled with cement,
mounted to the back of the fire box)

#1 is a bit expensive, and the Snorkel stoves I've seen for sale online
seem to be for rather small hot tubs. Besides, I already have a nice
wood stove that I'd like to use.

#3 is bad because the stove pipe expands/contracts and a tight fit is
hard to get.

I don't think that #5 will collect enough heat.

Which of the remaining options is best, and what are the
upsides/downsides of each? I'm leaning towards running the stove pipe
through a small water tank. (I could run it directly through the hot
tub water, except I want the wood stove set back from the tub by a few
feet). It seems like the easiest solution as far as labor goes, and the
big outdoor wood boilers use that method (though I've heard they make
lots of smoke, which would annoy the neighbors).

I am aware that soot will build up more rapidly than usual with any of
these methods, as the fire will be burning colder. Maybe pre-heating
the air or adding a blower would help to make a hotter fire. I could
combine the stove blower with a hot tub bubbler by pulling air from the
firebox and bubbling it through the water. I'd need a filter, of
course, to avoid dirtying the tub up. This would be a nice symbiotic
system, because normally a bubbler cools down the tub *fast*, since it
uses cold outdoor air.

Thanks for your advice and input.
Shamus

 

aberr8te@yahoo.com wrote:

have you seen www.cowboyhottubs.com ?



--
Steve Spence
Dir., Green Trust, http://www.green-trust.org
Contributing Editor, http://www.off-grid.net
http://www.rebelwolf.com/essn.html

 

Cannabalism comes to mind here....LOL

aberr8te@yahoo.com wrote:
have you seen www.cowboyhottubs.com ?

 

Hi,

Just noticed a typo. I wrote:

I don't think that #5 will collect enough heat.

I meant #6 (exchanger outside of fire box) won't collect enough heat.

 

Please excuse me if this is a double-post, I'm not sure if it went
through.

In my original post, there was a typo. It should have read:

I don't think that #6 will collect enough heat.

(leaving #2, #4, and #5)