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.

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

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.

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.

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.

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.

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 🙂

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.

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!

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.

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

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

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

For those that want a forced water system, a peltier device (or four) could use the waste exhaust heat to power a tiny water pump to avoid the steam bubble issue and circulate the water. The delta temp of the stove pipe and ambient would be a couple hundred C at least. A nice side-effect would be that as the thermal delta diminishes (stove is cooling), the pump stops circulating warm water into a cold stove. The resulting current is pretty small, so you'd need a few in parallel to boost the current for a tiny pump. You could also power the pump with batteries, and charge the batteries with the peltier device. The same goes for a super-cap. Edit: Apparently, the normal max temp of a hobby peltier device is around 70 C, so one side on the out-water and the other side using a big heatsink at ambient would be most efficient for that peltier device. If the water approaches boiling, the pump would move the water before it could turn to steam. The TEG (Thermal Electric Generator) type will operate at much higher temps as above.

Steve, could you fit a much longer feed chute so one could load longer sticks ? ie. pallet wood. This would mean fewer reloads... Great work, its an awesome product!

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. 🙂

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.

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.

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.

if you used a thermal sync like filling it with sand, would it make it be a smoother for the transition of the heat so you dont have the steam issue you are talking about? you could possibly then have a larger pipe run that can absorb the heat, if i am not totally wrong

Thanks for putting in all the work and time! I learn a lot with every video.

Outstanding build and the sand battery sounds like a great idea.

Man seems so happy with his setup. I can't wait until he discovers endless gas hot water. It will probably transcend him to a higher state of being.

Hi, been watching your builds for a while now, your workmanship is next level. I build a hot tub heater because there very expensive to heat on electric. I used stainless steel pipe due to chlorine in the water. It’s a fully pumped system with flow control valves. I can heat the hot tub to 40c in around 3 hours using old wood as fuel❤

Fantastic design and work,in my system I have the tank at a height above your rocket heater outlet this forces thermal syphon. My 90 litre closed system boils in about an hour on red box chips. Still loving your vids and awesome engineering.

Could you increase the diameter of the water pipes to fix the steam lock problem? More cold water = more heat needed to boil it to steam = you can keep the insulation and convert the wood into hot water more efficiently. Would the increased volume of water slow down the initial warming to the point where the efficiency gains of the insulation were cancelled out?

I think you should just build your tank around the rocket stove.. or build the stove into the tank. Just like a gas water tank works: the fire is at the bottom and the heat escapes through a tube in the center and there's baffles all through it. I think you should just put a rocket stove underneath that setup and let it exhaust the same way. I think it should be strong enough to withstand the fire. That will do away with the need for the pipes. Just design your rocket stove to slip under any gas powered water heater so that it can exhaust up through the middle, just the same.. that's how I would do it. Then your stove design would be so much more useful for people to buy... this is absolutely what I'll be doing in the future. lol thanks for the inspiration

Came for the rocket stuff, love the family interaction in your videos.

Water has a higher specific heat capacity than sand. Sand thermal batteries work well when they're allowed to get well above the temperatures at which water is no longer a liquid and you have pressure issues to consider.

Awesome project and very impressive work done. I hope you get to sell many of these :) As a biologist - side note on your "killing bacteria temperature comment": Bacteria start dying at 42C, but proteins loose their structure at 72C and above (which is why we drop items hotter than 72C by reflex) so yes, you are right - 72C is the goal. That being said - give it some extra heat if possible. Get it to 85C and you will be safer. Even at 85C - just reaching it is not enough - it takes time to kill ALL the bacteria. So you need to run it for 15-30minutes to be sure (that is, your bottom container water temperature needs to get there for that amount of time). That's why boiling at ~100C is ideal for this reason (the higher the temperature, the less time is needed to make sure they are dead). Hope this makes sense...

Well done mate, keep it up. love your work and your ethics of life.

Baby got big!!!!, great to see you back!!!

Awesome mate. I’m playing with rocket stoves too and trying to generate hot water. Very interesting seeing how you’re doing it and really nice fabrication too. I wish someone could see mine and give me tips how I could improve it..

Definitely interested in what you do, love how far you've come, keep the content going!

fun fact a lot of electric water heaters heat the top mainly, and then once the water at the top is hot they start heating the bottom! doesnt matter if youre only heating the water at the top if thats where your tap is after all

Just a tip - when securing with wire or cable ties(if they are long enough) wrap around twice before twitching.

I bet....insulation with a lowered draft....this would solve a few problems if it worked right. Improved thermal to water....and less fuel consumption. Would be interesting to see it as an experiment. Thank you for sharing and yes...superb welds my friend. Some of us could only dream of fabricating like that. Well done.

Those FIVE holes on the side of the burn chamber are allowing "secondary air" to enter, increasing the combustion efficiency. Good on you!

A stack of fire bricks around it would add to the efficiency. Great project overall though.

One more thing. You need a prototyping version of your arrive with thermowell ports all over it to take real-time template measurements throughout the system. Chamber temp, sand temp, inlet temp, outlet temp, etc etc.

to get the best out of the insulated setup a pump thermostatically controlled would be needed

Awesome! Would a spinning flow indicator in the bottom pipe be helpful? Help you see how fast the water is siphoning.

I thought you would've chosen glass wool for insulation, but that coconut stuff works too, since it should not get so hot as to burn it, even if it does you would see it get black at first, but I doubt it. Some engineers are especially safety people will demand otherwise :D I was thinking if you were to soak the insulation with lye (calcium oxide/hydroxide solution) water, would it get "concreted" a bit that would bring more fire safety in it are probably some heat retaining properties, albeit miniscule at that.

Very cool experiment!

Very cool video, I’m new to welding and you give me inspiration. Thank you for all you do.

Fascinating stuff. I would like to see you test Sand inside the box (for thermal mass) and insulation around the outside of the box (keep the Thermal mass warm and not a heat sink to the room temp)

Good work. Interesting stuff

Amazing job, liked your work! The air chamber seem to work better in not transmitting heat out. What about using a super white paint inside the outer skin, for reflection of the IR back to the working part of the system? Barium sulfate, check the "Tech Ingredients" video on the subject

Have you thought about using exhaust wrap for insulation?

Thats really cool.......well hot.......

I personally love the family men doing what they love and enjoying the process. Good work man. Your video inspires me to do things which I love. God bless you and family. Be happy and stay healthy. Sincerely Your one online fan.

my sister is going to want this for her pool :D could you instead of having one giant all the way around heating chamber maybe have 2 heating chambers? split the input, heat two portions of water separately and merge the output. Might save you from the steam problem while doubling your heat capture

it is far easier to wrap a pipe with the Teflon tape if you turn the roll over and apply it. You could pull out the old electric heating elements and install thermometers in both holes to monitor the temperature.

I believe you should add gravity fed wooden pellets and a hopper feeder.😊

Would also be a good idea to insulate the intake pipe, it also loses heat from the tank

Dont forget to add a sacrificial anode to the water tank, it should be installed in a way so its electrically isolated and or it cannot touch any other metals.

awesome thumbnail- This vid will go well

You can wrap the tank in even more insulation and make it even more efficient at holding the heat. Even just building a little insulated closet around the tank will help a lot.. Especially if it lives inside a cold shop in the winter.

What comes to my mind, in stead of sand and insulation. Water is great thermal mass keeper. So in the same reservoir tank, have second system that feeds water jacket, basically make the camber that did hold the sand, hold water and make lower level heating system. Like you said, only the top part of the large tank is hot, but if you heat the bottom part as secondary heater, more BTUs are brought to the system as an whole? So current system would take hot water from 1/3rd from the bottom and enter at the top, while the water jacket system takes water from the bottom and gives it out 2/3 from the bottom? Or even better, have second tank that is heated by the water jacket, and feed the primary system from the secondary system, so when you use the hot water, and fresh water comes in to the system, it is not cold water, but warm.

The difference in buoyancy of the hot vs cold air generates the draught required to feed the fire with air. If your air intake went down before it went up, then as the air is heated it expands and becomes lower density, being replaced by denser inlet air, then you can extract all of that heat back to room temperature and it can't make it flow backwards. You're unlikely to get it to match room temp, let alone get below it, so it will always want to rise more than it's surroundings. So basically, all heat out of the exhaust is waste. It also can, and should, be minimised if efficiency is the goal. If you think we're wrong then feel free to prove us wrong. Measure the air inlet rate with an anemometer, measure inlet and exhaust temp. Then if you're right then when the exhaust temp is ~room temp it should stop drawing air, but if we're right then it should continue to draw air. I think for this to work you'd need that U bend for the colder room air to fall down, and may want to let the exhaust go straight up so that you can maintain the momentum as it cools. So you lose less heat, but some energy is lost in kinetic energy in the draught created.

U r a awesome and amazing welder and engineer love ur videos. Question for u have u ever tried corn cobs or other fuels just wondering

You would do better to draw your cold water from the top of the water heater tank, through a tee at the cold inlet. This utilizes the dip tube, which hangs suspended above the bottom of the tank, in perfect position to draw cooler water through circulation, however NOT being in position to draw any sediment from the bottom of the tank. Doing it this way will not interfere with recirculation from either a pump or from thermosiphoning, should your heat source be situated below your receiver tank (as is often the case using solar heat). I built one similar that is made of 2 inch 14 gauge square steel tubing. I ran a single length of 3/4 inch soft copper into an oblong hole at each end of the chimney part (in and then out) and burn wood pellets. It makes quick work of 50 gallons of water and no steam all the time with no worries of sediment clogging.

Great video mate, I just couldn't see what you outlet was or where it was going. Is there any chance you could post a diagram of this. Thanks Mate. Cheers

Hmm... 🤔 A smaller variant of that would be perfect on my live-aboard sailboat. Warm water and heat... Great for winter in the baltic sea, wood is free to collect here..

Could a water pump help to speed up flow so steam cannot form?

You need a low power in line pump on the cold side. Power it with integrated TEGs so the setup remains passive.

Would one of those heavy rubber balls you buy at the pet shop for your dog work as a non block pressure relief valve just sitting on top of your pressure/expansion vent. just a thought.. Also by adding a flared out top to your boiler jacket and adding insulation to the outside of the jacket this would give a hot plate for cooking and help lower the extra heat provided by the insulation providing some functional duality

nice job 👍

good video, have you ever thought of building a rocket stove adapter for and existing wood burner, in other words that would bolt on the side of wood burner ,there are a few you tube videos on this item they would probable sell good,i'm going to build one for myself to burn wood pellets or wood chips gravity feed, jus a thought from sweet home Alabama USA

Great shear TY.

if you re-built it, make it smaller and install the insulation. It would be more efficient. and more sell-able if you want to ship them.

so lifting the tank and creating more pressure on the infeed, won't that stop it boiling because its going in faster

How much firewood does it take to reach some goal temperature?

Amazing! I need several of these for our people in the villages in our area Thank you for sharing this video Greetings from Madang Papua New Guinea!

Larger pipes to move water faster?

seems with the insulation, the inlet pipe should be further/higher away from the flame as the sand will be able to heat the water and not turn to steam.

Can you put a basket -or something- whit water over the top of the chimney, just for collect all the heat that you are losing?

I have a rocket heater with too large a thermal mass on the output, and it struggles to draw air properly - I need to boost the airflow with compressed air to get it started, and then it needs to burn really hot to work properly. So yeah, you definitely want a bit of heat left to help the air go up the chimney and suck fresh air into the front! ...I'm going to fix mine by building a bigger burn chamber, rather than shrinking my thermal mass, of course. More fire is better 😀

9:37 Assuming you did heat all 200l of water from 20°C to 76°C in half an hour would mean your stove transfers 26 kW to the water. Further assuming an efficiency of 50% you should have burned approximately 5kg of wood.

It might be because with the insulation, sand or fiberglass or whatever, its taking too long for the water to move through the system, so the water that is sitting closest to the fire is now getting too hot and cant push the water above it, so it turns into steam and you get that locking, when its not insulated, the water can flow easier because the temperature in the chamber is consistent and it isn't trying to heat the insulation and the water at the same time.

very interesting !

If the sand chamber had the isolation around it, that would reduce the surface for the heat too escape from after heating the sand allowing you to bring the temperature of sand and in tern the water heating chamber up makeing the thermal battery effect work at a higher temperature the problem is that the the heat being stored in the sand is being wicked away by the sheet metal where before where there's sand there was a pocket of air witch is basically just mild isolation so the outer sheet metal didn't have dirrect contact with heat too wick it away

Mate my Stanly socket set ratchet only worked for 3 months... must b something to do with living 30m from the ocean

i wonder, if having a thermal mass (sand) and heating that to it's max and THEN use cold flow-through the stove/sand water (no heated stand by tank at all) as a instant/on-demand water heater. perhaps heat exchanger might need to be changed to be more of a coil type to have more contact with the sand. interesting how long that setup would last, in the sense how much hot water you get out of it from a single firing and single heat charge of sand mass in the stove jacket? Also to make that equation more complicated and possibly more efficient and more off-grid - use solar heater as a separate system to keep supply 'pre-heated' and then send it through the sand mass to bring it up to heat faster. as for your issue with steam lock, i'm thinking it could be solved with larger amount of water per time. if you make larger intake (double or even triple) and then use in-line adjustable valve to control amount of water that being send into the exchanger. that should solve steam lock but also allows you to regulate (lower) out put temp as well as dial in proper flow for different combustion temperatures and fuel variations. great job otherwise!

how about you swap the inlet and outlet water pipes, so that the bottom water is heated up first? Will that improve the water cycle？

@ 7:05 U need 2 google search 4 a ... "Thermal Expansion Coefficient At Different Temperature Calculator" Or it... Can B expressed as V = 1/p = V/m V = Specific Volume ( m cube ) p = density m = mass of units Start temperature of 1 litre at 20'C To 60'C Will expand by around 0.01544 (This depends on the hardness of water) It will B way easier than me trying 2 explain it all in full... ... Basically 1 litre of water at a starting Temperature of x will expand x amount when it reaches a target temperature...

You could build an expansion tank at the top that just floats on water.

35kw or so?

That is a good example of a thermosiphon. How do we buy one off you?

Would it break the lock if the cold pipe arrived from below the heating chamber and went upwards, straight up the top and back to the tank, reducing the internal friction?

We had a slow combustion stove and water heater, the tank was mounted up high on a stand and there was a header tank above roof height with a snorkel for the hot water to go back into the header tank when it bubbled over, I cant remember exactly how it was plumed.

1. Raise the hot water cylinder up so that the cold outlet is above the hot outlet on the fire to stop steam lock and increase thermo movement of hot water 2. Cold pipe from hot water cylinder to fire must be at the lowest ( at ground level if can ) before entering the inlet pipe of the fire 3. Fit a t at the last 90° bend hot from the fire and have pipe vent out above hot water cylinder water level to release steam instead of trying going through the cylinder as steam wants easy pathway to vent out The mass and gravity of cold water will force water into the lowest point ( the firebox )

I would be interested to buy 1. If it comes to market. Please let us know in futur video

Im probably talking nonsense but what if the fluid in the heating coil was oil instead of water and a copper coil fitted inside the storage tank then indirectly heated the water? I would imagine oil would take a lot more heat than water.

Rockwool is the best hot insulation pretty much fire proof

Good day Steve, great seeing you and your beautiful wife today. Who was the cute minion on your back? Sand is great for a thermal battery. We are fortunate to have you leading and educating us as your explore this off grid technology. Wishing you and your family a blessed season filled with gentle, seasonally appropriate weather and restful evenings together with your family. Peace brother

If it's boiling then the diameter of your pipes isn't big enough to maintain the flow rate required to keep it below boiling. Fatter pipe and fewer bends.