heating a coil of pipe to heat water, then the house

there's not really a section for this idea, but I figure rocket stove folks will have opinions and perhaps even experience on this.

Most wood-burning-to-make-heat situations are all about gaining efficiency - using less fuel being the prime example. I'm in a bit of weird situation in the woods where I live. I'm in Northern California, in a fire danger zone, where the redwoods and other trees are constantly making fuel for the someday wildfire. so clearing out low fuel brush is something I am looking at doing every year from now on. I'm in a weird spot where I have *too much* fuel, especially in the form of brush.

Chipping is one answer, but I'm sure I don't need to talk about the unpleasantness of chippers here. what I do is wait for a rainstorm, then go out and burn a pile of brush. These are shoulder high piles that I break up and keep the fire going - in the rain- all day. I'd love to use this energy for more positive stuff. Like heating the water in my radiant floor system.

My radiant floor heating system is hooked up to pumps and the propane water heater. I've done a bypass and built a wood-fired water TANK heater, but due to site issues, it's not ideal. (another story) so, ideas are churning. Mostly, I need to get the heating element below the floor grade. which I can do with some longer pipes. But now to my question:

instead of a rocket stove or a water tank fire, why not simply have a metal (copper?) coil with an in and an out attached to say, 8 foot long metal pipes that are then attached to PEX with enough slack to be flexible. Add a pressure release valve or two, and SWING that coil into a brush pile fire, allowing for direct heating of the tube? As the water heats up, thermosyphon happens, heating the 8-10 gallons of water that sit in those tubes, which in turn heat my cob floor? If the pressure valves popped, or at temp gauge near the outgoing PEX got above 180, I could just swing the set up away from the fire...

why does this simple idea not seem to exist anywhere? what am I missing? would the copper break down too fast? would the water heat up too quickly for thermosyphon to happen well? am I really in such a unique spot of having too much fuel that this only makes sense for me? the only issue I see with this is I'll have to bring the brush to the coil, rather than do burns out in the woods.

maybe in 10 years, when I have the brush under control, I'd build something different. I'd love some input on this.

Tys; Just my opinion but... I'm thinking the coil will flash steam unless you have large dia copper/ stainless steel coil like 3/4" or bigger , and then the temp and weight of the metal will make handling it an issue. Thermosiphon might work but I would have a pump running the whole time. You're thinking of playing with hot water / steam don't get burnt !

Tys Sniffin : Here is a further back-up to what Thomas Rubino said ! I will go 1 step further and state that 3/4 inch Copper or Stainless Steel on a thermo-syphon

system will not be able to carry the heat away fast enough and you will need 1 1/4 line or bigger -especially with any distance between your burning brush pile and

your receiving/holding tank !

Try this on for size, a 1'' pipe is half the diameter of a 2'' pile, both its Cross-sectional area or number of square inches is only 1/4 of theC.S.A. or square inches,

Also the relative % of the perimeter or surface area of the smaller pipe is proportionally higher, this means more flow lost to friction ! So you don't even get the

Full 1/4 Flow!

Ask any Fire-Fighter Vol. or Professional, this is one of the 1st things they teach at Fire-fighters Essentials !

Along with the increase in diameter of your piping and Boiler Grade Temperature and Pressure Relief Valves add circulating pumps, and you have a system

requiring vetting by a H.E.V.A.C. Engineer, Annual In$pection$, And about an Associates Degree in Further Training/Education to avoid becoming a victim of the

Dreaded 'Boom Squish'- Depending on the level of the Skill Sets you bring to the project at the start !

I hope this message was timely and useful, Think like Fire, Flow like Gas, Don't be the Marshmallow ! For the Good of the Cause ! Big AL

Tys; I'm glad Big Al posted with that information , seems it's important to a firefighter to know those numbers off the top of their head... lol . Anyway another safer thought for you could be a metal stock tank filled with water and your brush piled on around it. You would have to bring your brush to it but ... no danger of explosion !

Tys Sniffin : Here are a couple of open systems that truly ought to be safe to operate, but notice this system was designed around Domestic hot water
and not designed for primary heating !

Links Below !

https://www.youtube.com/watch?v=YTnr8ua54Uw
https://www.youtube.com/watch?v=1oDpmmsqHwQ


For the Good of the Crafts ! Big Al

I know I know, don't blow yourself up. I totally get that, and sincerely thank you for the concerned warnings.

When I built my first go-round on this, a gas water heater system with the gas bits yanked out, a cob base with horizontal fire tube using the 40 gal tank as the chimney, I added 2 pressure valves set at 150. They worked great.

I do find the point about a copper (1"?) coil just going to steam rather than just pushing hot water - that's something I've not seen or thought of. has anyone actually seen that? I suppose I could set up a test with an open system (barrel of water feeding my wand coil with other end in empty barrel)... it's just that testing that commits me to buying some pieces.

My conceptual problem with the 'boil the coil' thing is getting the thermosyphon to work without having to weld an in and out on the barrel/pot... if you just drop a coil in a pot, the IN tube ends up at the same height as the OUT, ruining the thermosyphon possibilities. know what I mean? to have an OUT pipe lower, I generally see people feeding the water pipes into the side of the pot... which needs sophisticated joints in a fire, not something that would leak.

I'm going to scrounge around and see how much I'd actually have to purchase to make an open test system.

AND, to move away from this idea - anyone have any examples of fire water heating with a BIG firebox, rather than a small rocket stove set up? I'd like to feed my fire by the wheelbarrow load, not the armload or handful. the smaller my firebox, the more work I have to do with a machete.

Tys Sniffen wrote:AND, to move away from this idea - anyone have any examples of fire water heating with a BIG firebox, rather than a small rocket stove set up? I'd like to feed my fire by the wheelbarrow load, not the armload or handful. the smaller my firebox, the more work I have to do with a machete.

Outdoor wood fired furnaces.

Tys Sniffen : Yes we can ! After a Short period of stagnation, (20 yrs) with little design change occurring ( Well lots of attempts at re-inventing the wheel and creating
'Flaming Units of Death') Recent developments include The Creation of Horizontally Fed, Batch loaded, Rocket Mass Heaters RMHs, and Masonry Bells that will greatly
simplify the Creation of new RMHs that merely need to be fed 2-3 times a day ( For all but the very coldest climates) And still give us the freaky high temperature
burns that provide clean operation and high efficiencies !

These units will require Additional Skill Sets beyond the still great efficiencies of simple Rocket Mass Heaters, For many of us the learning curve will be steep,
and the days of $50 - $100 weekend Workshops are gone forever. As much of the new advancements can be understood as piecemeal additions to the traditional
RMHs, this is the 1st thing to learn, and from there your Fellow Members and near neighbors here at Permies.com will help show the way !

Before we move on, to finish up on Boom -Squish a couple of links Below :


https://www.youtube.com/watch?v=jbreKn4PoAc
https://www.youtube.com/watch?v=BZEIqG2RrMs


For the good of the Craft ! Big AL

just to retread this again - you guys are basically saying you don't trust pressure valves? I fully and completely get the dangers of blowing up a steam box, but isn't that the beauty of these things?

pressure valve As I said, I put two of them in place on my last experiment, and they worked great.

here's my 2 minute attempt a drawing out my thought. perhaps my description was good enough. I always intended a BIG copper tube, at least 3/4 inch.

https://docs.google.com/drawings/d/1u2sWKq5TstLAb15m3goDw7QKw10OZyOSMTgA6oA0zSs/edit?usp=sharing

I was thinking I'd do an experiment with an OPEN system to see how fast it would heat up, or if it would go to steam too fast or something.

Tys Sniffen : I want an open system with no pressure relief valves to fail, and potentially blow my house up ! Seriously, in that Micro-second when water
flashes to steam the expansion ratio is just over 1700 Times.

Think Boston Marathon Bombing, only with more fatalities, and full thickness full body burns ! And this will be people you KNOW, Family !

For an acceptable pressure relief valve for back-up on an open / un-pressurized System see this link :

http://vimeo.com/11954163

(I do not know this gentleman personally, just that he makes good 'Kelly-Kettle' type camping water heaters !)

I have a second type of acceptable back-up pressure release valve Which I need to look up!

Because you are using a solid fuel, which can not be shut of in an instant by closing a valve, at that point where you wish to stop heating water you
still have all that heat to deal with !

Solid fuel Boilers are still under a total ban in the Entire British Isles ( Last time I checked)

Open systems that can not be pressurized are however possible ! ( there is no Paradox, its two separate things !)

Think like Fire! Flow like a Gas! Don't be the Marshmallow ! For the Good of theCrafts ! Big Al

Late post : This next devise insures an open system, is very cheap and allows the internal water level to be checked, and does all this while minimizing

water vapor loss, and the need for make-up water !

Note that this is part of a open combustion wood stove, its creator is happy with its inefficiencies as shown by the smoke production and the amount
of heat he gets for the time spent feeding his system !

Link below :

https://www.youtube.com/watch?v=oiwnYqcRLZw#t=16

The part I think you want to watch starts at 16:20

Finally, if you have so much wood have you considered burying some in a Hugleculture Mound ! Big AL