Big rocket stove water heater V2

I have done a fair bit with thermosyphoning and I can see a Limitation in your system straight off. The outlet pipe comes straight out and then goes up. If you had the outlet come straight out and up without the horizontal piece, you would do a lot better. It would strengthen the thermo syphoning and greatly reduce any boiling. This should be able to be done just by removing the horizontal piece out of the stove and going to the riser from the elbow and then either joining or getting a double length piece at the top. Better still, go at a constant angle with NO horizontal Pipe. 45 out the stove straight into the top of the tank. Despite what the safety zealots and clueless will say, you CAN use reinforced Vinyl tube as it is rated for higher than boiling water temp and the vessel is not sealed. That's what I use and despite going a bit soft, it's more than fine. If you wanted to go over the top, use heater hose. This will make the thermosyphon much stronger and easier for any steam in the boiler to escape up and out and greatly reduce and most probably eliminate the boiling which is obviously NOT a good thing. I would also put a header tank at the top where your overflow is. That will attract heat so insulate it. You would only need a 10mm hole in it to vent steam and limit and heat loss. This is done in a lot of industrial boiler systems with a Cistern valve in the tank. The other thing would be to insulate the stove. When you put sand in it you made a lot of surface area for the heat to radiate to atmosphere. This may be OK if you were trying to heat a living space but is wasted if this is outside. I would also suggest leave the internal of the stove empty but wrap insulation around the outside if you don't want that to act like a radiator. I built a House heater with a waste oil burner heating an old gas spa heater heat exchanger. I had that going into an insulated 200L Drum but this year I am upgrading to a 400L hot water heater. The burner heats the water through the HE, a small circ pump transfers the hot water through a 3/4 hose into a radiator in a box with a fan which draws the air though into the house. I did it this way because there is no chance of fire or water coming in the home and frankly, I din't give a rats about any efficency losses, I am happy with the peace of mind trade off. The burner can go up in flames while I'm asleep as I run it all night, the hoses can leak and put 400+ l of water everywhere and I don't give a damn because it's all outside and far enough away not to matter. That said, last 3 years ran perfect. As a matter of interest, the thermal capacity of taking the 200L of water from 23C to 76 gives you 12.3 KWH of stored thermal energy. If you take that capacity and divide it by the time it took to get there, you get the energy input into the water. 30 Min would be 24.6 KW, 1 Hr would be 12.3. bear in mind an average water heater element is 3600W on that sixe heater so you are doing well. If you WEIGH the amount of timber you put in and measure the heat rise till it is burnt or near enough, you could work out the efficiency you are getting. wood is pretty much universal in BTU content by Weight so you could get a near enough measurement. From what I could deduce from the vid, I would say you are doing pretty well. Real nice build and will be great with a little tweaking.

Ease your firing rate after initial heat soak. Fired quite a few steam generators and boilers in my time. The insulation is a good step, but now you need to learn to drive it. You need to adjust heat input to match heat loss + heat absorption. Firing at full bore will out pace heat absorption. Had experience on boilers from a few kWs up to 660MW. It is a bloody good job, don’t sell yourself short mate. Here is a plan, as soon as as you are getting water temp rise, throttle your air inlet damper and control your burn rate and ensure water temp continues to rise. In your job you should have an infrared temp gun yes? If not get one you’ll use it every day for pre-weld heating. Bloody good job! Thanks for posting, keep us in the loop. P.S. fire control will vary during usage, but auto damper control could be developed, YOU have the smarts, trust me.

First guy I have seen that mentions an "open" system, so many people use wood stoves to heat water tanks and it makes me nervous as they dont take into consideration they are potentially building a bomb. I work in an industry dealing with high pressure boilers daily in an industrial setting. We have controlled water levels and redundant pressure relief options with both automatic and manual controls. Without it being an open system you MUST control water level and you must control pressure constantly.

Fantastic result. Heating 200L to 75 in 30 mins is very impressive. It's not an exactly fair comparison but 2x 2400W immersion heaters take 30L of 18C water to 75C in about 15 mins in a steel keg on a cold day where I live.

I would say that the sand option would be better than an empty chamber as the thermal mass would heat the room long after the fire is out. As for steam locking, have you considered increasing the pipe diameter to allow a greater flow through the heat exchanger. Most old heating systems I've come across that heat the water cylinder by gravity alone use a fairly large diameter pipe (28mm). Also mounting the header tank as high as possible may help a bit.

Loved the build and the test. In my view the dampness in the sand has kinda spoiled that part of the test. Heating it will try to boil off the water first and restrict sand temp to 100 C or less until its dry. I think it will be worth trying properly dry sand if you want the thermal battery effect. Good to see chooks and family still included 🙂

This kind of system (at least the principle) is pretty common here in Finland, and also eastern Europe and parts of Germany at least. In my case, I have a 3000L tank, which is coupled to a wood gasification burner. It is pressurized (with an expansion vessel), and the tank is purely a buffer (the hot water for domestic use is taken out with a heat exchanger). The system also drives the underfloor heating.

30 minutes to heat from cold and you still have hot water the next day? Wow that's awesome.

Used to have this system on our farm 50 years ago now - now power or water. Only change I would make is put this heater in my house so I don't have to go outside and it heats the room - olden days are back. We used to cook on it as well.

Full marks. I was worried for a while this device would not be properly agricultural, but you got there with the tie wires! Full fencing wire is the gold standard but some wire is good enough. ✅ Suggestion: in the full install with the cold water reservoir at height as proposed you can run the pressure relief pipe so it drains into the top of that reservoir (not needed really but a lot neater); and, on the question of insulation, there is a potential sweat spot with partial insulation. The steam locking may be less of a problem with insulation on the outside of the cavity, or just the top half. Also, just like @PU-hi6tg, you could consider putting a one way valve in the return line at the bottom so steam has less ability to push back. From my perspective the system should be optimised to heat the water (i.e., insulation around the heating section), there is plenty of heat radiating from the rest of the unit to keep the shed warm.

You have to run both the input line from the tank and the output line at the bottom of opposite sides, the coldest water will be most dense, so make the output from the stove aprox 2.5 cm above the input drain. The hot water will rise through yhe water column and heat the surrounding water. Keep the sand as this will improve efficiency, but only over longer time scales, run a hot fire for 6-8rs as if you were heating in the arctic, and the water and sand will reach an equilibrium temperature and then hold it for a longer period of time. Also, if you utilize an up to down to up organization of the exhaust side of the rocket stove, the reversal in direction will allow for more surface area for sand, and thus hold a higher temperature of sand and therefore water. Add an oil drip function for burning waste vegetable oil and motor oil as a fuel, and you will have a machine that would be worth 10k$ in alaska. Great work and thanks for your videos

With regards to insulating the riser, consider using a polished finish on the inside surface of the cover while leaving the space empty. You seem to have a perfect scenario for an infrared barrier. Would be keen on purchasing a set of plans for this one. Am currently building an off-grid home. It has a thermally insulated slab with radiant pipes for the main sink amongst other buffers. Great work! Cheers!

as a plumber that used to work on open and closed hw systems, you've done a good job. If you intend to raise your cold feed tank, you will need to raise the open vent up and over the cold feed tank, the hot water off take would normally be taken off the vent, but as you technically do not have any temperature control on your heat source...I wouldn't do that. The cold feed will become the expansion for the storage tank. You will need to raise the open vent at least 600mm above the cold feed tank because as you know water expands as it heats. You will learn about parasitic circulation as you put your pipework into practice. Just a thought, check out back boilers...if you intend putting sand around your fire box.....you could put your circs at the rear and use 25mm primary circs for your thermosiphon.

Good ! Try using a check valve

The insulation worked better than the sand because the sand is more thermally conductive, so it effectively increases the surface area available to radiate that heat from, where as the insulation reduces it. You would need to insulate the outside of the sand to get the benefit from it, but if it's not getting above water temp then it's no better than the same volume of water would have been. Water has about three times the energy storage capacity per unit volume up until over 100°C.

You’ve done a great service to humanity with your experiment / creation. Bravo!!

We used to have a Crown wood burning oven with water jackets and a 600L tank plumbed in. It was also an open system by the top pipe extended about 9 feet up with a 45 degree bend near the top. When we heard VERY isolated rain on the roof we knew the tank was boiling. Damp sand can soak up and store an incredible amount of energy. One issue is that the heat in the sand will still escape through the outside wall (hence you could feel it was hot) whereas the insulation doesn't let the heat out, but also doesn't store any energy to keep the heating going after the fire goes out. Sand in the cavity, insulation wrapped around the outside - that is the configuration that would probably get the most out of it. It wouldn't look as nice, though.

I think if it was in a cabin or something like that, you'd run it for room heating too. In that case the sand would be the go because it'd have plenty of time to build up the heat in the mass and hold it for overnight room heating, much like the traditional rocket mass heaters do without causing the steam lock issue that happened with the insulation.

All I can say is OUTSTANDING. Outstanding welding, outstanding explanation of what your doing and your an outstanding Aussie having a red hot go. I'm keen to see a version 3 as I can tell your not 100% happy and when you sell them put my name down (seriously). I have a little property north of Newcastle and plenty of timber lol.

Older buildings, especially farm houses here in Sweden often have old water heating systems. The rule for dimensions is 2 inch pipe between the stove and the tank and 1 inch pipe from the tank to the radiators. No electricity or pump needed. Open system just like yours. Maybe the pipes are a bit thin? Nice build, this one and other. 🙂