rocket bath?

Has anyone tried heating a bush bath with a rocket stove of some sort?

Marion Kaye wrote:Has anyone tried heating a bush bath with a rocket stove of some sort?

You can also use surplus m67 military heaters.



Some people have experimented with flowing water through copper tube coils around the heat riser of a rocket stove, as a water heating device.

I was thinking more like this:



Or perhaps, more realistically, this:


Or as a last resort, something like this :-


Not sure wher that high techie looking thing would fit in

Those are cool designs, I like the more realistic one. Like the picture with the tub on the burn tunnel I would incorporate the tub as part of the thermal mass, and surround it in cob.

I've seen quite a lot of stuff with complicated gizmos and lots of tubing, seemingly intended to get near boiling water out of a tap, and a lot of them seem to be doomed to failure as they are trying to use the hottest part of the fire, ignoring the fact that the presence of non pressurised water in that region is going to take so much heat out of the combustion that it's going to seriously reduce efficiency.

But I don't want boiling water. Just a warm bath.

Marion Kaye wrote:I've seen quite a lot of stuff with complicated gizmos and lots of tubing, seemingly intended to get near boiling water out of a tap, and a lot of them seem to be doomed to failure as they are trying to use the hottest part of the fire, ignoring the fact that the presence of non pressurised water in that region is going to take so much heat out of the combustion that it's going to seriously reduce efficiency.

But I don't want boiling water. Just a warm bath.

I wonder if you could use a tempering valve, like on a modern furnace to automatically mix the boiling water to warm.

http://en.wikipedia.org/wiki/Thermostatic_mixing_valve

You could also use iron pipe instead of copper, instead of wrapping it around the heat riser, make a radiator above the barrel out of iron water pipe, so it is sacrificial and easy to replace.

Steve Harvey wrote:Those are cool designs, I like the more realistic one. Like the picture with the tub on the burn tunnel I would incorporate the tub as part of the thermal mass, and surround it in cob.

Yes, I think the tub would be better placed as a heat mass rather than directly over the fire too. I'm hoping someone on here has actually tried it and can report back.
In particular, I'm wondering about water condensing issues, as a tub of water is going to keep the mass below cooler than a dry bench would.

I have played with heating water in a bath on top of my RMH. As has been stated the problem is in the tendency of water to reduce the effects of the heat riser to preform as it is sopposed to. I was able to receculate water through a bath with a small pump and an insulated container. The limitations where that I could only raise the temp slitly with each pass through the heat coil. It takes a lot of BTU's to heat just the bath, them with each pass of the water through the coil the temp in the bath would drop significantly. Geoff Lawton has a video on you tube showing a dedicated system to heat water this seems the safe way to do what you are asking about.

Mikael

I will soon be bathing in this cast iron laundry tub that I picked up for free. I'm mounting it 2 feet off the floor, just above the horizontal burn chamber. It will be cobbed in. Water from the pots will give it a faster response time.

Wait, Dale, you fit in a sink?

That must be a big sink!

Anyway, I am deeply interested in wood fired hot tub things, preferably with the added efficiency of rocket stovishness.

It's a big sink and I expect to squat at best. I'll call you for help if I get stuck. I may use a weighted shower curtain that would allow me to stand and pour water over myself and have it run back into the sink, without splashing everywhere. It will only be used for bathing temporarily, until I carve a giant red cedar bowl for the purpose. It will then be a dish and laundry sink. Laundry and dishes that are allowed to simmer for hours, require very little soap.

I'll be very careful, so that I don't topple out onto the floor or onto the hot rocks or cook tops.

I have bathed in many solar heated garbage cans and other vessels at job sites. There have been no incidents, except for the few customers who arrived unannounced.
..........
My bathing plans changed dramatically yesterday. I paid $50 for a roof mounted hot water system with three big panels and a tank that appears to be around 80 gallons! There's more than $50 worth of copper.

Solar hot water is awesome. We had a system in Wisconsin, it filled all our needs at least 5 months of the year, and helped year round.

Something I'm thinking about is a cob hot tub.

Becky Bee wrote a book about building a cob hot tub. She advises anyone who has bought land and plans to build a (cob) house, to start by building a cob hot tub. It makes everything that follows that much nicer.

Here is a page about Rocket Stove Baths
from a guy in Kent (England).

Love that cob hot tub, Julia! I had been about to shelve the idea permanently, but the simplicity of that one has put it back on my list of projects, as a separate project.
Love Dale's rocky rocket stove too. (I had already bookmarked the thread of it's build. )

Just an idea, make four walls, 5 or 6 ft tall. Plonk an old metal bathtub on top. Build a batch rocket underneath. And use a ladder to get in the bath. I think a batch rocket and a brick bell ough to concentrate the heat enough on the bathtub. The old enameled cast iron ones should do the job.

hehe That's what I thought might have to be the case when I starteded this thread, but Julia's link https://rocketstovestuff.wordpress.com/about/ covers all the bases, simple construction, basic materials, no cooling the fire/loss of efficiency, and with the added bonus of no hotspot to worry about.

There is one thing I think might be a bit dubious about it, and that's the length of horizontal before the chimney, but I'm guessing if it's slow drawing, a bit more height would solve the problem (?) and a few embers dropped down the chimney at the start would help get it going too.

Marion, this is the type described into "the book" but frankly, i think it's a waste of fuel, and nowhere near efficient.

If you had a "hill" you could do something nice, with a rocket underneath. Using a bell.

This is the largest cast tub that I have ever had to move. More than double the weight of a claw foot. No takers on the free add, so it went for scrap.

I have a standard sized bath that will do nicely. It's been lurking in the hedge for years, well, it didn't start out in the hedge, it kind of grew into it. I stashed it there years ago, hoping to make a grey water reed bed system with it. Now, clearing that part of the garden for other reasons, it's come to the surface again, and in the interval between it disapearing and reappearing, I've heard about bush baths and love the idea, and seeing as it's cast iron (hard to come by nowadays) and pretty much anything will do for greywater, it would be wasted for greywater. (I have at least two small (attic) water tanks not doing much which would do nicely. )

Satamax, In what way wasteful? Also, I don't see the use for a bell for heating a bath, it's either heat wasted before it even gets to the bath, or an unnecessary complication after. Please explain what it's for.

Marion, my take on it, you build four walls, high enough to acomodate the height of a heat riser and the bath on top, may be with a 4 inch gap. And use the bathtub as the bell's top. I Wonder what would be best,leave the whole volume Under it open, and let the gases stratify. Which in my mind would be best. Or fill it up partialy, to have higher temps, but faster exhaust?

Get it? That would be nice outside, with raised platforms all around. If for Inside, i would make the same kind of bell only lower and make the heat riser come around where the tap's holes are. In that case, i would insulate the Inside of the bell, to concentrate all the heat on the bath. Since you're not heating the water directly.

In this later case, you could gain a bit of height by embeding the feed tube and burn tunnel in the ground. Which means this would necessarily be a J tube. While for the tall type, with the heat riser comming Under the bathtub, i would use a batch rocket. May be a 4 or 5 incher would do. I haven't calculated the BTUs needed for a bath.


I'm thinking of another one, completely different. Based on this batch rocket. Open the skp file.

https://permies.com/forums/posts/list/80/40007#352982

Basicaly the top of the firebox would be the bottom of the bathtub. (instead of the cooking plates!) And you would have the heat riser right at the side of the bath, covered with a double barrel, which would have water between inner and outer skin. Obviously open to the surounding air. You would fill the bath slightly, let say 15cm of watter, and top it up when it's about warm enough, with the water from the double skin barrel. You could even make two bells each side of the firebox. For gathering as much heat as possible.


How does that sound?

Marion, the bell is where secondary combustion of wood gasses happens, thus greatly increasing the efficiency of the stove. In most rocket mass heaters, the bell is made from a 55 gallon steel drum. Inside the bell is a heat riser, which is basically a chimney. To be more precise, the actual secondary combustion happens inside the heat riser, which is inside the barrel or bell.

Paul's article on rocket mass heaters is here. Scroll down for a schematic, to explain what the bell does. Paul calls it the "super rockety reburn combustion chamber."

Satamax wants to have the tub on top of the bell, since that's the hottest part of the system.

This is something I would love to build this summer. Where I am the sun doesn't always shine and the wind can be cold, making for a less than ideal solar shower situation. A nice hot bath heated with a rocket stove would be so nice.

As far as having the tub above the barrel/bell to get the most heat, maybe sinking the rocket stove in the ground is better than raising the tub above the barrel.

Julia Winter wrote:Satamax wants to have the tub on top of the bell, since that's the hottest part of the system.

Just for clarity sake Julia, I believe the hottest part of a rocket stove/mass heater is somewhere around half way up the inside of the insulated heat riser. Of course this doesn't really help us when designing to heat water in a tub though and for the sake of that I think you are correct in saying the hottest place to capture heat for the tub is from the top of the barrel/bell.

I have a steep, south facing slope. A sloped riser could be built on a 45 degree angle and a 3 foot bell at ground level. A tub inserted here, would be easy to enter. A black riser would start the process on its own, when it heats in the sun.

Julia Winter wrote:Solar hot water is awesome. We had a system in Wisconsin, it filled all our needs at least 5 months of the year, and helped year round.

Something I'm thinking about is a cob hot tub.
.

Would love this. My husband though. Cracked me up when I sent him this link. "That could also be used for a cannibalism site" AHAHAHAHA

I'm intrigued by the idea, ever since I saw a Cowboy Hot Tub (Cowboy Hot Tub) and built a simple galvanized pipe coil that I would stick in a fire to heat water for camping or use to heat a 150 gallon rubber maid tub full of water.

The problem with all of these ideas is that it takes a lot of energy to heat 50 gallons of water (or 100 gllons of water) along with a tub and any cob or other connected materials hot enough to enjoy as a jacuzzi. To heat 100 gallons of water from 60 to 100 degrees requires around 40k btu's. If you're including heating the tub and a bunch of cob as well, that would be a much larger amount of heat required. Unless you're planning on running your heater all day or you've got some ultra efficient, concentrating design, it's a rough challenge.

I've been playing with and building a couple variants of this idea, a roman bath rmh to heat water in an aquaponics system and using a rmh to heat water for a jacuzzi. The aquaponics rmh works great, heats the greenhouse and gives a bunch of heat to my aquaponics system. I have a plastic liner 1' high sitting on a sheet of permaboard covering a series of brick channels that the exhaust from my rmh runs through. The barrel heat heats the greenhouse directly, and the exhaust heat heats the fish water. It's hard to calculate the heat transfer in my system, I have 600+ gallons of water that is flowing across a table, mixing with other water and coming into contact with other objects. But the exhaust is almost never above 80 degrees exiting the chimney, so it's possible to use a design like this to capture quite a bit of heat. If the barrel were insulated or the exhaust somehow more directly channeled into the ducting system, an even greater percentage of the heat could go into heating the water.

Having played with a couple of ideas for heating the water in a jacuzzi directly, I built and tried a simplified rocket mass heater design, using a radiator sitting on top of an open barrel with the jacuzzi water running through the radiator. As long as the water is flowing through the radiator quickly enough, pretty much every bit of heat generated by the rmh seems to be transferred to the water. Again, the problem I found was that it takes a ton of energy to heat 100 gallons of water from 60 to 100 degrees and even with this direct system, it still took almost 4 hours of burning to get the water hot enough. I've got a thread looking at ways to improve or redesign the rmh -> radiator model, maybe a batch box with 8" riser (mine was standard J tube with a 6" riser) could burn more wood and generate more heat/hr and speed things up a bunch, but while I love the idea, the simple realities of the amount of btu's involved, the energy content of wood, the rate at which wood can be burned in a controlled environment and the degree to which that heat can be transferred to water show why a nice, natural gas 150k btu heater is an impressive invention

My current working on the problem is based on changing a few of the variables. Instead of heating the water from ambient temperature, I'm using a passive solar heater during the day to heat the water to roughly 80 degrees and then covering the hot tub (I use a 150 gallon rubber maid tub) to keep as much heat as possible. That preheating alone cuts the but's required in half. If I can do a bit more work on the insulation, after I heat it up at night, I cover it again, and then when I start solar heating during the day, it'll already be 80+ degrees, so little by little, I'm hoping to be able to keep the water around 90 degrees and then only need a 30-40 minute rmh fire to get it up to a nice, toasty 104 degrees.

I'm definitely interested. Love the photo series explaining the goals!

Outdoor Bathtub:
Have seen the cast-iron with firebox underneath model done at Cob Cottage Co and elsewhere - Ernie calls them "people cookers" and they need a wooden seat to avoid scorching the meat. I mean bathers.
Probably something can be done to improve the firebox - a little clay tile between fire and cast-iron could do wonders for both fire temperatures and bummed-out bums.

Immersion Heater:
Have also seen "snorkel" heaters and have some ideas about doing a double-lined pocket rocket with some thermal mass, to keep the fire temps up but transmit heat to the tub as an immersion heater.

Heated water/ on-demand heat, piped in:
Tim Barker's rocket water heater
does great for multiple showers, and might be the best all-purpose rocket water heater I know. Certainly from a DIY standpoint, this is about as simple as it (safely) gets.
His basic brick J-style fuel box gets 55 gallons up to temp over a few hours, then they run a heat-exchange coil through that water to provide hot showers. The design is pretty robust, and you can add a lot of insulation to limit heat loss and maximize your hot water for fuel used.
I could see doing a couple of these for bigger loads, or pairing it with an outdoor kitchen rocket-canning-kettle stove that you can drop a coil in the canning kettle for hot-tub occasions.

Less Fuel:
Most of us know how hot a simple garden hose can get in the sun. Direct solar water heaters use the same idea - coils, loops, or flaked zig-zags of pipe or hose (usually a high-temp black pipe), in an insulated box under glass for cooler climates, with good pressure-relief so it can't boil and explode. The right design can be set up to thermosiphon from a tank, reducing or eliminating the need for pumps.

If you are a good high-temp plumber, I could see setting up a solar hot water thermosiphon to get things up to temperature most of the time (and to circulate the water so it doesn't stagnate as badly). Might not need supplemental heat most of the year in some climates. If needed for winder, add a rocket "booster" to make those steamy moments a reality.

Less Water:
What about flexible water volumes with some kind of stepped design? If you're sculpting it anyway, could do a hot tub where the foot-well is shaped like a regular bath tub. Heat just enough water for solo bathing, or upscale to a guest-friendly 4 or 6-person hot tub when occasion demands it. If you're only doing this a few times a year with guests,.

I would probably do this workshop for half-price the first time, or if anyone wants to come over to my house to build the first one with me, I might not even charge for that "class."

-Erica

Ooh! Ooh!

(hand up)

I've got a big lot in NE Portland that's just begging for a workshop derived rocket fueled hot tub! I wonder what it would take to set up a workshop in Portland. . .

If you only want to heat water for a bath then you could simplify Tim Barkers design http://permaculturenews.org/2013/05/20/how-to-build-a-rocket-stove-mass-water-heater/ and make it a low preasure open system. All you would need is the in and out pipes and a 3rd as a preasure relief. This would be vertical with a "shepherds crook" top to prevent things blocking it.

Heat the 55 gallons then empty into the bath.

Is a rmh for an outdoor bath perhaps overkill? We simply dug a hole in the ground on a small bank. The bsath fitted snugly in the hole. From the lower side of the bank we then dug under the middle of the bath, a pit to build a fire in and an escape route for the smoke at the back of the bath. I suppose you could say that that formed a more or less j shaped firebox with the bath as the top surface of the firebox. It heats the water to bath temperature pretty quickly. It's best to let the fire die down to embers before getting in the bath and essential to sit on a towel! It's lovely to have a bath that doesn't cool down while you're soaking. The embers are enough to keep the water at a good temperature.

ROCKET MASS SAUNA TUB:
My vision is to make a stockade style log structure* on a sandy slope with enough height that you could build the batch box under the floor then the riser and barrel could be inside but the fire loaded from outside. Have the exhaust from the bottom of the barrel enter the space between a cement board surround of the tub and the tub and travel around the tub and up the chimney beside the barrel. cover the surround with cob and waterproof the surface. Clamp a barrel on top of the one with the heat riser and fill it with water. Add piping to bring cold water to a faucet end of the tub and a valve to pipe water to the top of the barrel. Pipe water from the bottom of the barrel to the hot water faucet. The sauna would probably get up to heat before the water so you could sweat for a while then rinse off and then fill the tub and soak if you wish.

*Stockade style log structure:
If you have a saw mill like the one at Wheaten Lab you can easily cut a tongue on one side of a log and a groove on the other then they fit together like car decking only vertical. If you cut a tongue on the top of your foundation log and a groove in the bottom of the wall logs they lock together. The ceiling logs are the same except that you cut a groove in the side where they set on the tongue on the top of the wall. Then all you have to is put some cob on top of the ceiling logs to make a slope add a waterproof membrane and some moss and you are all set except for making a door.

This is one of the simplest hot water heaters http://www.campingwithhillbilly.com/hot_water.php Is there ageneric name for these?

A large one in an institutional rocket stove could be a good way to get bath water.

I've imagined a cast tub, set and sealed with an air chamber around it. Kind of like the barrel around a stack in a rmh. Exhaust could pass around the underside of the tub and heat the water inside. A damper could direct the flow of exhaust from its normal mass storage, into the tub wall air - exhaust chamber. With a braised drain, there's no reason you couldn't drain it like a normal tub. The water could be preheated via another system. I have also wondered what a system would look like, if you passed water through a container of heated stone or sand, that drained into a tub.
http://www.bing.com/images/search?q=rocket+mass+heater+tub&go=&qs=n&form=QBIR&pq=rocket+mass+heater+tub&sc=0-21&sp=-1&sk=#view=detail&id=7CB5F76458CB3F0C76175654042004C2EE347AF4&selectedIndex=54

I use a rocket pocket entirely immersed into the water. It works great. It is like having a fire inside the water. Zero heat lost through the walls of the barrel, but all the heat transfered into the water.

Sue Rine wrote:Is a rmh for an outdoor bath perhaps overkill? We simply dug a hole in the ground on a small bank. The bsath fitted snugly in the hole. From the lower side of the bank we then dug under the middle of the bath, a pit to build a fire in and an escape route for the smoke at the back of the bath. I suppose you could say that that formed a more or less j shaped firebox with the bath as the top surface of the firebox. It heats the water to bath temperature pretty quickly. It's best to let the fire die down to embers before getting in the bath and essential to sit on a towel! It's lovely to have a bath that doesn't cool down while you're soaking. The embers are enough to keep the water at a good temperature.

I'm also in NZ where outside baths are common and I've used them a lot. I think the tech Sue refers to could be improved with rocket stove designs, but not sure of the value of adding mass. Basically you want direct heat, as hot as possible, under the bottom of the bath. Insulation is good, and clean fast burning will mean less wood is needed, but the build up of heat in mass seems counter productive to me.

The UK example linked above https://rocketstovestuff.wordpress.com/about/ doesn't strike me as being more efficient time wise, but he does say he uses about half the amount of fuel. He's taking an hour to heat a bath, a normal wood fire under a bath should take less than that. I heat a bath currently with a 3 burner gas stove, windproofed but not insulated and it takes about around 40 mins depending on time of year. Whatever you use, start heating when you are filling the bath, not with a full bath of cold water, and have a cover on the top of the bath to stop the water from cooling.

These guys below have gone ultra high tech, expensive but very efficient and built to last. It uses rocket stove tech without the mass to heat water, and a convection loop to circulate water through the heater and back into the tub. Burns very clean (no smoke when used with dry wood). It's designed to heat a large hottub size tub but can be adapted to a bath (or any large container of water). It burns wood, pinecones etc, or you can get a gas adaptor.

http://kiwitub.co.nz


http://kiwitub.co.nz/technical/howitworks.htm

chad Christopher wrote:I've imagined a cast tub, set and sealed with an air chamber around it. Kind of like the barrel around a stack in a rmh. Exhaust could pass around the underside of the tub and heat the water inside. A damper could direct the flow of exhaust from its normal mass storage, into the tub wall air - exhaust chamber. With a braised drain, there's no reason you couldn't drain it like a normal tub. The water could be preheated via another system. I have also wondered what a system would look like, if you passed water through a container of heated stone or sand, that drained into a tub.
http://www.bing.com/images/search?q=rocket+mass+heater+tub&go=&qs=n&form=QBIR&pq=rocket+mass+heater+tub&sc=0-21&sp=-1&sk=#view=detail&id=7CB5F76458CB3F0C76175654042004C2EE347AF4&selectedIndex=54

That's what I was thinking originally. The link shows an improvement on that, and is the type I will be trying. (Actually the same one as Julia linked to earlier in the thread. )
I don't see any point in complicated plumbing and gizmos for really hot water; A bath doesn't want really hot water, just warm bath temperature water to soak and wash in, not turn the occupant into cannibal stew.

Rose, I think there is possibly some point to a cob thermal mass in addition to the water. I think it may help keep the water warmer for longer. (More mass -> more heat stored -> longer time to cool down.) ?

Sue, I think the inverted bell system is more suited to 'indoor' heating, as a lot of heat is given out from the bell. This (the one in the link above)
is just a basic insulative cob rocket stove with added mass, or to put it another way, a basic bush bath made more efficient by the use of an insulated chimney and firebox.

The burn tunnel on that rocket stove looks extremely long, I wonder if that would actually work well. How much wood do you have to burn to heat that much water and cob? Is burning wood all day to heat bath water really the most efficient way to heat bath water? what about solar?

I would rather see something like this indoors rather than outdoors, that way you could also use it to heat your home and add humidity to the air in the winter. Burning wood in order to heat bath water seems a little wasteful, when there are other heating options out there, that do not require burning trees.

I have a feeling that the whole point of these outdoor baths is that they are outdoors. For everyday bathing, certainly indoor facilities will be much more efficient, in temperate climates. (There could be climates where that is irrelevant.)

Who said anything about burning trees? Perhaps I should mention that my interest in rocket stoves etc. comes from years of bonfires, of all the twiggy stuff that just isn't practical to burn indoors, that still has to be got rid of and would take way too long to compost. Right now I have four big heaps of twiggy stuff, and that's just from last year and not counting the logs still in store, or the ash tree that is mainly going for craft projects.
If I can use some of the mountains of stuff that goes up in smoke every year from my garden to heat a bath or cook something on, so much the better. I certainly won't be burning decent logs for it! Although, tbh, as I can't fit a RMH in my house, it probably would be more efficient to use the logs for the rocket bath than put them on the open fire to heat the back boiler!

Trust me, if indoors was an option, it'd be indoors!!

hmmm... there's a lot of black clay in an area I'm working, have to test that clay for heat stability (was considering clay oven, but not sure my clay is sufficient) and now this thread sparks my imagination in making a black clay bath ... somehow... I don't know what it entails in this moment... my intention is to move the black clay that blocks water from flowing down on this lot so, there will be a fair amount of black clay to be used somehow.

Pia Jensen wrote:hmmm... there's a lot of black clay in an area I'm working, have to test that clay for heat stability (was considering clay oven, but not sure my clay is sufficient) and now this thread sparks my imagination in making a black clay bath ... somehow... I don't know what it entails in this moment... my intention is to move the black clay that blocks water from flowing down on this lot so, there will be a fair amount of black clay to be used somehow.

Nice work!