Thermosyphon Rocket Spa Heater

I saw one of these:



It follows the same principle of the house heating outdoor boilers but much smaller. There is a water jacket around the fire. I'd like to make a DIY rocket version and sketched one with coils wrapped around the duct that normally would be in the cob mass. Read an older posting here and it was recommended not to water jacket the barrel, instead coil the first five feet of the duct with the hot water push nearest the barrel and the siphon side on the other end. I suppose the exit under the barrel could go to the duct either straight out then up (as shown), straight up next to the barrel or wrap around the base before going up. The box with the pink is insulation around the coil. It was suggested that this placement would not rob the barrel of the heat needed for good combustion. As this would be outdoors near the hot tub, the heat off the barrel would be wasted as far as heating the tub. Any ideas on how to grab that barrel heat for the water without killing the clean rocket combustion, thanks.

Welcome Chris. I don't think you need the barrel. Just a burn tube with the coil at the upper end would do it. The barrel is all about creating a pump and radiating heat to a room. Check out the water heater on Geofff Lawton's site. It's here somewhere too, but I don't know the title. . Someone drop it in please.

Those water jacketed units don't allow high enough temperatures for clean combustion.
-------------------------------------
I just hit 3000 posts. That's a lot.

Dale Hodgins wrote:Welcome Chris. I don't think you need the barrel. Just a burn tube with the coil at the upper end would do it. The barrel is all about creating a pump and radiating heat to a room. Check out the water heater on Geofff Lawton's site. It's here somewhere too, but I don't know the title. . Someone drop it in please.

Those water jacketed units don't allow high enough temperatures for clean combustion.
-------------------------------------
I just hit 3000 posts. That's a lot.

He has an interesting method, I like it. With outdoor home heating boilers the outdoor water is not mixed with domestic, it uses a heat exchanger. Geoff's heat exchanger is a coil through a heated mass non-pressurized water tank. While white boarding the design he says the air from the burn swirls around the water tank, not sure if that is natural turbulence or he has deflectors. Below is a screen grab off his video of the design. Anyone know if the water in the coil would thermosyphon if the height/distance to a spa was correct?

Would it be feasible to make a small version of this to heat just enough water to wash a sink full of dishes? I'd love to have one in my kitchen. I was thinking of a 5 gallon bucket or a propane tank that's been refit, instead of a 40 gallon water tank. Do you think the water would be inside the coils long enough to reach a nice temperature? And then, would that be big enough to have a shower off the same system later? or a bath? I guess I just want my hot water now, not an hour from now.

If the the safety steam vent coming from the inside the water-tank had a whistle from a kettle on the end of it you would hear when the water inside to starting to boil and you could make fire adjustments if necessary.

Awhile ago I was reading about Finlanders that make all kinds of water-heating apparatuses for their sauna's and hot water needs. That lead to a site with a nice pictoral of how a guy lays copper coil in a steel box and then pours a cast of plaster of paris into it. It is then installed on the side of the woodstove.

http://www.michigan-horse.org/preheater/



This got me thinking about if this had any applications to rocket-stove water heating systems. The plaster of paris wouldn't likely stand up to extreme high heat but it might work in some uses like on top of the barrel. Also I was wondering if refractory material could be used instead of plaster. Anyhow , just throwing it out there. Might be a dumb idea... might have some uses.

alan stewart :You are the new kid in the class so testing you on the stuff we did last week is not fair ! However you raised some points, last one first !

Refractory materials work by reflecting some of the heat energy they are exposed to- Back into the heart of the fire. With firebrick that has a high %
ofAlumina-Silicatesthe higher the temperature the fire brick gets, the higher proportion of heat energy it Reflects or Refracts back into Your Rockets
combustion chamber.

Refractory materials surround by good insulation helps bring up the temperature of our burn to the freaky high temps that makes our Rocket so efficient,
AND does it ''More Quickly ''. Not what we want when we are trying to absorb heat energy!

So here is my question, If it was 75F when you covered your Rocket Mass Heaters RMHs Feed tube and went to bed, and it was 68F when you got up, and
62F when you got home how long will it take you to make a fire ? Answer not very long as your system is holding lots of heat, and it will draft well right
from the start !

It took you 5 minutes to start a fire and 20 minutes later the roar of your own personal house dragon that lives in every RMH is a little softer, you check
and yes it will take more and bigger wood, and the internal glow of the Refractory bricks lining your burn tunnel are already changing from dull red to
cherry red !

Next question requiring a fast,correct answer -Mother Nature does not grade on the Curve !
Your Tea kettle you have plumbed into your system starts to whistle, How do you safely remove heat from your Water Thermal Mass and how are you
going to to replace it,

Extra credit for knowing what to do when the power goes out !

There is an automatic prize if your whole family knows the correct answer, they do not take part in the lottery to see who gets excluded from the gene pool

You have a good imagination and can grasp ideas intuitively, keep plugging at this, the problem is there is no way to turn off the Heat which within the core
of your Rocket can easily see excursions to 2400dF ! As you know water boils at 212dF and water flashing to steam expands 17,000 Xs!

For the Good of the Craft, Think like Fire, Flow like Gas, Don't be the Marshmallow, as always, your comments and questions are solicited and welcome ! Big AL !