Rocket hot tub on skids for Wheaton Labs?

Hi all,
Ernie and I are getting ready to visit Wheaton Labs again for this year's Rocket Innovators event.

I want to do a hot tub.
The heater element seems do-able, I have a couple ideas for how to do it.
But getting a hot tub ready that meets the Lab's standards for durable, natural materials seems a little daunting within the scope of the Innovator's Week.

I asked Paul if he is interested in dedicating any space or resources toward a hot tub, and he shared the following thoughts:
1) Hot tubs seem really attractive. There might be a lot of interest, and it might add to the romantic potential and general loveliness of people's time at the lab.

2) Water sources are likely to change over time - they're hoping to have water available up on the Lab soon, but can't guarantee it until it happens. Also, workshops happen in different places.
So Paul's first choice is: Let's build it on skids. If it's on skids, he's in. If he has to pick a permanent location now, it seems like he might end up wishing it could be moved later, and that could be frustrating.
(Maybe after water sources are more stable/plentiful, a permanent location or a second hot tub could be considered.)

3) Some of my suggestions (redneck hot tubs, stock tanks, used hot tubs) raise red flags about materials and toxicity. As with all Wheaton Labs projects, Paul is not interested in buying plastic, galvanized metal, or other toxic gick to make this happen. There are some lovely cedar hot tubs out there and that feels like more the style of our aspirations.
(Likewise, this will most likely be a fresh water soaking tub that is emptied after use, and the water used for other things, because adding salts or chlorine to water to slow bacterial growth makes it toxic to plants. What's the point of 'saving' water if you make it toxic and non-usable? Sharing it with plants is more my style, so that's the direction I'm interested in going with this project. Scaling the project to the available water sources, and the weekly or monthly water needs for the gardens and other purposes, seems like a good fit at this time.)

4) There may be other details to work out, like whether heat comes from below the water (like a giant cooking pot) or whether it's a side-heater that circulates. Or an immersion heater.
I have ideas for simpler and more complex heaters that could work with the drainable soaking-tank-on-skids approach.

5) Hey, we have this forum where you can gauge people's interest by starting a thread! So I did.

The first question is:

Is anybody interested in actually showing up to build a skiddable hot tub?


The shape and size of the hot tub itself may be determined by the level of interest.
Donations of cedar planks, or possibly aluminum (Paul is OK with it, I'm skeptical), might push the project in a definite direction.

Let's leave any discussion of heating methods aside until we know if the project is actually going to happen.
(I confess I'm more interested in trying my own ideas for the heating elements than listening to other peoples' ideas about the fire element itself. However, if you are actually coming to the event and want to collaborate, I'm much more open-minded, as that makes your skill set and enthusiasm factors in what's possible.)

Yours,
Erica

Drains:
I want to be able to conveniently drain the hot tub, once it's cooled enough, into a nearby cob stomping project, garden area, or swale. Maybe even use it as a reservoir for fire or wash-water. However, I don't want the drain to get knocked around when moving the structure.
The skiddable platform probably needs a stout, boxed-out area for the drain and fittings, so they are protected from rocks and brush in case it gets skidded up onto some rugged surface near a project site.

Wood fuel:
Fuel storage could be combined or separate.

How much wood will it take?
It takes roughly 8 BTU to heat 1 gallon of water by 1 degree F. There are 8700 theoretical BTU in one lb of bone-dry fire wood, or about 6000 actual reclaimed BTU in most reasonably-dry wood that burns in reasonably-efficient conventional stoves and furnaces.
So a pound of wood could heat 100 gallons of water by 8 to 10 degrees F.

If the water starts at 55 degrees, and we want it to be about 90 F for a lovely hot tub (could be up to 110 F for some people's comfort), we are talking about 40 to 60 lbs of wood per 100 gallons of water. If we're efficient as all heck.
More likely 100 lbs of wood per 100 gallons of water, if we are less efficient.

The smallest stock-tank soaking tubs are around 4' diameter and hold 150 to 250 gallons of water (275 for a cube 4' tall, 155 for a round tank 2' tall).
Minimum for a tepid soak would be about 100 to 200 lbs of wood. More likely, especially with a larger tub, to use a hefty load (500 lbs) per firing.

It might pay to stage this next to a portable woodshed, or allow space for a palette of wood next to the heater (1/2 cord, or about 500 lbs). It will pay to treat this as a community special treat.

It also will pay to insulate around the tub; perhaps it will be a double-walled thing, or if it's wooden sided then there might be a quilted, waterproof fabric skirt of some kind. Probably we want wool or perlite underneath it except where the drain and fittings (heat?) go.

It might be worth doing a two-level tub: a 2' by 5' basin for a one or two person soak, which is the foot well for a larger round tub that can hold 6 or 8 people for a large-capacity soak.
Or it might be even smarter just to start small.

I'm also open to doing a solar collector for pre-heating the water. A black-lined tub could be smart too.

ok I am far from an RMH genius but the idea I get reading this is... a boat on a trailer. except you put the water and the people in the trailer and build a rockety sort of heater on the trailer.

think biiiiig wood barrel : https://c2.staticflickr.com/4/3004/2341110225_b40d271cf7_z.jpg


now think heating coil added into rockety design :
http://www.captivatist.com/2014/01/20/wood-fired-hot-tub-dutchtub-heats-organically-3.jpg


actually I got a lot of half decent ideas from image search 'wooden hot tub'. the only thing would be to making it water tight and placing the drain. then the fun of heat tube through the water and the RMH or RMH in the water etc.

Erica,

This is a great project! DH and I have been talking about an ofuro for years, after using them in Japan. Have you seen the Snorkel Tubs? I wonder if they'd share some data on the efficiency of their stoves for heating water. Or even a loaner tub for the workshop
One thing I've read about wood tubs like these is that they need to have some water in them regularly or they leak as the wood shrinks.

Erica Wisner wrote:
I'm also open to doing a solar collector for pre-heating the water. A black-lined tub could be smart too.

Solar is for wimps Erica. Add moar fire!

- An alternate suggestion, these heavy duty units a super durable easily portable, and not unlike the billboard tarps that are being used for water
Barrier membranes for the Wafati's Umbrella s so they shouls at least be considered !

As past experience has taught us, the Rocket Mass Heater RMH Core can be built in less than a day !

I believe this meets the portability issues, and the acquisition of and availability of a couple of portable tanks offers many possible uses in addition to
hot tub use !

http://www.firetak.com/portable-water-tanks.html

http://www.alibaba.com/product-detail/Collapsible-and-Portable-Plastic-Water-bladder_718498260.html

This is a small sample of what is out there, Off of the top of my head, a one day operation

1) clear off a large flat area minimal attention given to making the area level - though with two (2) tanks the higher one can be of a dark material
and sited for solar gain, Then draining by gravity - heated by passing through a 'made on the spot' RMH, and finally ending up in a second tank
repurposed to use as a Hot Tub !

This Does point up the issue of where do you get the water, and how do you transport it , and suggests a solution by getting a

used pumper/tanker from a local vol. fire company for small money and again this can have many uses stacking functions !

Shared in an effort to stimulate thinking outside of the box ! For the Crafts ! Big AL

I think Paul and Jocelyn have been eying this one up...

This system is a nice freeze proof drain back space heater, that could be used to just preheat water instead. The idea is, a small pump only runs when there is sun. Sun equates to enough warmth that the small lines will not freeze in the collector. When there is no sun, the system simply drains back into the storage tank, or in your case, hot tub.

http://www.builditsolar.com/Projects/Water/SolarLoo/SolarLoo.htm

Burra ; Yes ! That is certainly a step in the right direction, however I Think that it would actually increase the location/portability issues

if Paul insists on not having a permanent location at this time ! There are suitcase sized portable pumps for grass and low woodland fire fighting

that can be used for many other purposes -stacking functions Again - this is a modest proposal to open up others thoughts as what can be possible !

For the Good of the Crafts ! Big AL

Late Note : : On a closer examination this appears to have been built as a ''Red Neck" Hot Tub -with little pumping ability ( Recirculation only ?)


Miss- matching metals has probably already created many weak points that will place this build during its next attempt to be used, and may even have
doomed this build to early failure !

a.L.

I have a portable hot tub and I went with the copper tube in a BBQ. It works very well, however it may not be right for you. I'll share some of my learnings with you just the same.
1. Soldered copper tubes have a real risk of de-soldering if the water ever stops flowing. I have an electric pump to push water through mine and it does not take long for the copper tube to boil dry if anything stops the pump. I used swage-loc joints instead of solder and bent tubing instead of 90 degree bends.
2. Propane may seem like a cheat, but having the ability to minutely control the temperature on the fly is great. Never too hot, never too cold.
3. Insulation is key. I built my 6'x6' tub out of plywood and 2x4's (framed like a house) and lined the inside with 2" styrofoam sheets. Not very permie perhaps but very comfortable to sit on and lean against and with styrofoam laying on top of the water, the tub is still warm in the morning. I tried my heater on a swimming pool and found that without the insulation, I could not get the water beyond 'warm'. Not really even up to warm as I recall. A simple plywood shell is probably somewhere in between.
4. Double layered tarpaulin is enough to keep the water in. One layer is probably enough but if you run two layers, you can afford to have holes in the tarp and as long as holes don't line up between the two layers, it won't leak (much).
5. 1-1/2 hose used as a syphon drains the pool fairly quickly with no need to cut holes in the tarp for a drain.
6. 2x4 construction with 2" styrofoam enables me to break the tub down like an Ikea flat pack for transportation.

I don't have any pictures handy.

A more permie insulation solution might be to use a ring of haybales with a strap around the outside to keep everything in place. Two layers of haybale and a double tarp should do the trick quite nicely. As long as you have 20 or 30 spare haybales.

I should have included fuel consumption in my previous post.
A 20lb propane tank heats my water from well temperature to hot in about 8 hours, maintains the heat and with the lids on during the day the tank makes it another night. Or maybe not quite all night for the second night depending on how hot I run it and how long I have the lids off. Generally the lids are off from 8pm until way too late for any sensible person to still be up. Two 20lb tanks last me a long weekend and that includes replacing the water once.

My tub is approximately 6'X6' X 28" deep.

My husband and I have been looking at stainless steel dairy tanks. There are some that are big enough that if cut in half, you get a decent sized hot tub, with a drain.

We planned to build a redwood liner for actual sitting upon, and some sort of structure to insulate the tub from the outside. The mechanics of heating the water, well, those haven't been worked out.

However, there do seem to be a fair amount of used dairy tanks for sale, maybe ask Paul if stainless steel is OK.

Maybe there are some ideas here?

- Just throwing the idea out there, as this is an innovators workshop and a hot tub is being planned for - how about inviting Becky Bee !

If you don't ask, you will never know if she is available ! For the good of the Crafts ! Big AL

http://www.kiwitub.co.nz/home.htm

Above is the link I was meant to put in my last post...Doh!

from the web site above. The gallery is a fun read, with charming descriptions of the stories behind the photos. The heater uses convection to move the water, no pump. It's usually fired with propane, but can be fired with wood, they say it takes about 50% longer.

Definitely couldn't come out there to help with the build but wanted to throw a few thoughts out. We'll start with the destructive thoughts since they always suck.

First, the portable part of this makes a lot of things I would run to pretty much impossible. Preheating is the ultimate factor in my opinion as burning some 500lbs of wood for a soak seems like WAY too much.

To keep things portable, a 2 ton thermal bank is just not practical for obvious reasons. Specifically, a large thermal bank (RMH bench) that you embed your piping into for preheating the water (RMH heater core @110*F will preheat water run through, say, 100ft of pex or copper pipe).

Secondly, the plant friendly part of this brings up an interesting problem...the water always has to be fresh. No one wants to get Legionnaires from the hot tub, so that makes a simple solar preheat system that much more complex - you'd need to use something like propylene glycol or other suitable fluid with high boiling point along with a heat exchanger so you don't have your soak water sitting around days on end getting up to a manageable temp.

I'd hate to think of you guys out there burning a whole winter's worth of heating fuel just to have a 3 hour soak, but preheating is very troublesome.

The idea of using a more suitable fuel for heating the water comes to mind - biogas from a methane digester, or maybe wood gas - but these systems are difficult to implement and wouldn't work during a 1 week lab.

Since I'm such a downer, I have to make sure I get to something constructive:

How about a flatbed trailer that can handle a large thermal bank/RMH? It could be tugged around as necessary with a tractor. Might have to get creative in making the thermal bank more durable to vibration and shock for such transits, and might have to make the heater core something you can teardown/rebuild on the fly, but ideally any travel to new locations would be something that only happens once or twice over the years. This makes the preheating part easy and the mass is able to double its usefulness as a heat source (when it's not being robbed for the hot tub). After running through a maze within the thermal banking, the water would finish heating up to desired temp using a rocket stove, or perhaps even with several trips around the barrel of the RMH itself.

Another thing I should add is that solar heating water inline, through a coil of black hose/piping, works REALLY well when the sun angle is good and the clouds cooperate. While in Florida, even during the winter months, I had hot shower temp water, at least 110*F, coming from 180ft of spray painted garden hose coiled up on the ground. The water was cool beginning the journey - no more than 60*F - so it definitely received a nice temperature bump. Summer months, the water temp was often too hot to use straight and had to be tempered with cold water! Here in the north, however, it doesn't work that well and is really only suitable in late spring / early summer, and only on sunny days. Adding more hose/tube length would help but also slow the water flow considerably, so using insulated housing and glazing, mirrors, fresnel lenses or the like would probably be needed.

Solar preheating would definitely be my go-to for preheating water during the nicer weather but winter months would have to rely on a RMH thermal bank or similar, and that's really when a hot tub is most welcome.

Otherwise, when it comes to holding water, the standard water barrel technology should do the job beautifully while remaining portable - cedar, oak, etc. I like the hay/strawbales idea too, but while the liner (pool liner, vinyl tarps, etc) would do the trick well enough, I don't know how much toxic crap that stuff might release into the water, especially hot water.

I thought I read on a homesteading blog that someone used peroxide to keep their soaker tub water clean. They were using a metal or poly stock tank for their urban homestead. They would add peroxide prior to a nights soak and let it bubble for a while. The peroxide degrades to form oxygen and water which should then be safe to drain afterwards.

Robert Reid wrote:I thought I read on a homesteading blog that someone used peroxide to keep their soaker tub water clean. They were using a metal or poly stock tank for their urban homestead. They would add peroxide prior to a nights soak and let it bubble for a while. The peroxide degrades to form oxygen and water which should then be safe to drain afterwards.

Good point - know from experience that plants love hydrogen peroxide, too. Ionized or colloidal silver is another possibility for this - had a neighbor in Florida who was a partner in a business selling copper/silver ionizers for swimming pools back in the 70s (they're still sold today by many). The copper stops algae and other organic growths while the silver takes care of pathogenic organisms. For a hot tub setup, the main concern would be pathogens so ionized/colloidal silver would do the trick on its own. A small PV setup could generate enough for it and that would help reduce the need for fresh water supplies (less need to tug the thing from place to place following available water sources) and increase the plausibility of preheating with solar and other methods.

Let's not spin off into the whole blue smurf people debate...was just a thought

Some one here has suggested getting an old tanker from a local Vol. fire dept. to get water to your Rocket Hot Tub on Skids. As a member of a Vol. Fire Dept myself I'd advise against it. All kinds of toxic gick could have been put in the water tank on those trucks. There could be chemicals in it meant to help put out fires and funky stuff that got washed into whatever local pond it may have been filled from in an emergency. I suppose the tank could be cleaned out but I don't know how it could be done. This is true if you get a tanker (1,000 to 2,000 gallons of water usually) an Engine (1,000 to 1,500 gallons) or a brush truck (anywhere from 200 to 500 gallons).
There are smaller and larger versions of all those types of trucks but those are the general sizes I've seen around here.

Just finished building one a couple of weeks ago, with an outdoor bath rather than a tub.
Its not been built as I had hoped but it works nevertheless.
More rise on the pipes, a return flue pipe in the mass and less insulation around the drum would have improved overall efficiency. Insulating the water heater itself should also improve things. Photos attached are of the first burn out of the core and then the nearly completed setup. I can post more pics if people wish. The bath itself is insulated and the pipes are lagged.

And here's some information about fuel use for the Kiwitub :-

Multifuel - heat it with wood, gas, coal etc..

Firewood, coal, or other solid fuels take a bit longer than gas. The same burner is used.

To heat the tub using firewood place the stainless steel grate in the burner and build a fire on it just as you would in a pot belly stove or woodburner. Long thin lengths of dry firewood are best, fed frequently. Coal can be added to give more heat.

Once the fire is established, usually no smoke is observable from the flue, just shimmering air. Like an outdoor barbecue, it is acceptable under clean air regulations in New Zealand except for some specific central urban areas. Check with your local authority. Gas is acceptable in all areas.

Fire safety: The copper waterjacket encloses the burning chamber so the belly of the burner sitting on the ground gets no more than warm (say 40°C (104°F) max.), plus the flue cowl has a stainless steel mesh spark guard. However, if in doubt in dry conditions, run the burner on gas, not firewood.

Heating time: This depends on the temperature of the water to start with, the dryness and type of wood, how good you are at making a fire, etc. Say two hours or so starting with cold (13°C (55°F) water to heat the tub to 38°C (100°F).

(It's about enough time to welcome friends, feed them a meal while periodically putting wood on the fire, and get the tub hot enough for bathing by the time of the coffee and liqueurs.)

Or Heat it with Gas

The same burner also uses gas.
Faster to heat the tub on gas than on firewood: can take less than an hour and a half.
Uses 3 kg or so of LPG to heat tub usually: cost in NZ approximately NZ$6.00.

To heat the tub on gas, just place the stainless steel tube burner (supplied) in the burning chamber and light the gas.

The tube burner is a long slim stainless steel cylinder which puts out 127,000 BTUs (equiv. 32kW)/ hour of heat. The gas hose is stainless steel mesh with a Teflon inner lining, connected to a childproof regulator with POL fitting. Just screw into the outlet of a standard gas cylinder, usually 9kg (cylinder not supplied).

When the tub is hot enough, just turn off the gas. It's that simple. The tub is extremely well insulated: the water will stay suitably hot for bathing for many hours.

Time and Cost: Gas heats the tub faster than firewood. The time varies a bit depending on the initial temperature of the water, weather conditions, etc., but is usually well under two hours. Our record is 1 hour 25 minutes from 7°C (45°F) cold winter water to 40°C (104°F). This required 3 kg of gas, costing NZ$6.00. In northern New Zealand, the tub has been heating up in less than an hour, e.g. 45 minutes on Waiheke Island.

Generally in the Southern winter, it will take about half a 9kg bottle of gas to heat the tub from cold and keep it hot to use for 2-3 days. In northern New Zealand, it's more like a third of a bottle. Most of the gas use is in getting the tub hot from cold. Once it is hot, turn the gas off and it'll stay hot all that evening; put the lid on and the next morning it'll take only 10-15 minutes on gas to get it up to bath temperature again. We've never had any problems, but the water should be emptied after 2-3 days of personal use. In a commercial situation, we recommend emptying it out the next day. Just fill with clean fresh water or seawater for your next soak.

This reminds me of a video I saw a long time ago with a cob structure, cob oven/hot tub that I thought was so extremely cool. An improvement upon it would be to heat it all with a rocket stove!! Cob sealed with linseed oil may make a wonderful tub! I know you wouldn't be able to move it, and I know that many are scared to put clay and water together...but I'd be inclined to give it a shot. How gorgeous is this?



Cob Hot Tub Video

I have a question and a suggestion. Are you set on the design of heating from outside the tub?

I ask because if you heated from the middle like a Kelly stove, it might heat faster with less fuel.

Ganado Mage : A picture is worth a thousand words ! links below :


http://fancy.com/things/144251977893681441/Kelly-Kettle-Stainless-Trekker
http://tinhatranch.com/wp-content/uploads/2013/07/Kelly-Kettle.jpg


So- For anyone that is unfamiliar with the '' Kelly Kettle '' here is a couple of pictures

Much more handy than the Cast ironware the Hobbits took with them when they invaded Mordor !

Ganado : It Comes down to efficiencies. The Rocket Mass Heater RMH burns at such freaky high temperatures that it comes very close to the

theoretical limits of any wood stove, and burns so cleanly that Besides the heat produced there is near zero particulates/smoke mostly CO2

and Water vapor !

Trying to directly surround the RMHs core with a water bath cools the fire down to a very Smoky in-efficient burn. This is acceptable with a Kelly
Kettle because by design the small amount of water is balanced against the limited amount of Fuel that can feed the fire. also that small amount
of water can not be pressurized - popping out the cork 1st .

With the flame front around 2000º Flowing the water around the outside of the Fire through a coil can and has caused the water to flash to steam
This steam explosion is referred to here at permits as Boom - Squish

Think the Boston Marathon Bombing only with more deaths, and more full body full thickness Burns !

For the Good of the Craft ! Big AL

Several comments here.

1. In about 1987 or 88 while in college the dorms for an activity brought in a trailer with a wood fired hot tub permanently mounted on it. That one there were 2 burn chambers on. The first was for the large fire for initially heating the water. It was on the hitch end of the trailer and took about 4 foot long logs. The chimney for it came up as a large box in the middle of the hot tub capped by a stove pipe. Once it was hot initially they took that stove pipe down leaving a metal island in the middle with seats. at either end. The second was a small heating coil with a small wood fire that the circulation pump for the hot tub ran through. The water temperature was regulated by choking the small fire down. To set up they pulled in and put some really heavy build in jack stands down. A stairs at the rear folded down. They then filled it with water and lite the fires and plugged in the cord for circulator pump. Other than the metal island in the middle it was a standard fiberglass hot tub probably rated at 14 or 16 people. It was an over width trailer slightly.(probably 10 feet if memory serves. There was a plywood deck with hand rails around the tub. You were a long ways in the air so the hand rails were necessary. So what if you either build on a skid that was designed to be high or just build directly on a trailer? What if the bell for a standard 8 or 10 inch j tube rocket came up in the water then you thermal siphoned off the chimney as it came out from under? For the second stove the smallest rocket you can build heating a coil being circulated by the circulation pump?

2. Also from college a suggestion for the building material for the hot tub. That is concrete. Now I can hear you now quickly ruling it out because of weight. But it doesn't have to be have to be heavy. I had several friends that while in college participated in the concrete canoe contest. When they got done the canoe probably weighed about twice what a similar fiber glass canoe weighed. It was built using two sizes of styrofoam beads as the aggregate and fiber to reinforce and an air entrained concrete mix. To get a really good surface finish the skin was poured using low aggregate/more concrete mix that was troweled on and then the rest was cast inside it. Now I can see you blowing this out of the water for use of plastic beads. But my question is can Vermiculite be used in the same way? Sealing the surface will be vital because of vermiculites ability to absorb water. But could it be successfully used in place of the styrofoam beads to produce a really light weight mix?

3. As for using a bunch of wood to preheat the water what about cheating just a bit here and going solar My brother heats his small backyard swimming pool with 50 or 100 feet of small black poly tubing and a small fountain pump. he just scatters the coils out on his lawn. On a bright sunny day he can have the pool up to easily comfortable from a cold water fill and the cost is the tiny bit of electricity to run the pump. You will already have a pump installed so the added cost would simply be the poly tubing to scatter out.

4. Now about the purification issue a sand bio filter would give you sum minimal protection. To beef things up even more but avoiding toxic chemicals what about a small ozone generator and water purifier set up. Ozone rapidly dissipates from the water and would be less of a threat to soils where you are dumping the water. It can be generated on site using just a little electricity. Don't know if it can be used for hot tubs or not but simply throwing it out as a possible.

A charcoal filter??

I have worked out how to pump water for a hot tub from a pond or well, into a hot tub, using only firewood as the energy source.

I wasn't entirely sure about this one, until Marcos told me that I had re-invented the steam injector.(300 year old technology) They are used to inject water into steam engines against great pressure.

Your tub would be one of a kind, if the fire pumped the water.

https://permies.com/mobile/t/33312/energy/Dale-steam-powered-jet-pump?foo=a

We turned a precast concrete manhole into a hot tub. It's heated by our Garn wood fired boiler. It stays full all the time and is well insulated so uses very little extra heat. In the dead of winter, we need to fire the boiler for an extra half hour or so in order to make up for the heat loss of having the cover off while we use it. With a well insulated tub, keeping it full and hot is the way to go. We do not use any chemicals to treat the water. We use sphagnum moss strips from Spa Naturally. Some day we might find a local replacement for the sphagnum. The moss strips go into a the strainer compartment on the circulator pump. The circulator runs all the time. Yes, it uses a little electricity all the time, but is much more efficient than refilling the tub each time with hot water.

OK, but what about my original question? Anybody currently in range of the labs interested in actually building such a thing before October?

Thanks for all the great ideas and project reports.
I'm particularly interested in the combination of peroxide/ozone/filtration to alleviate the wood-shrinking problem. I don't have a problem with leaving water in the tub and then discharging/refilling when needed; however too much algae would definitely be a turnoff for some people.

I'm substituting "pathogens" for that Legionairre's reference.
From previous threads: Legionairre's is a pneumonia risk, only caught in a shower scenario, where microscopic droplets are inhaled. It would not likely cause infections in a soak-bath scenario. But there are other pathogens that can, which tend to proliferate at lower temperatures than Legionairre's. (Legionairre's is nasty because it tolerates hotter temperatures than other microbes, meaning it can be present in water tanks that are set low for energy efficiency like around 120 F. Other stuff dies by then.)

If the whole volume of water is brought from cool and clean up to hot temperature relatively quickly, pathogen risk is less.
In general, I would encourage people not to use a shared hot tub if they have open wounds or infectious disease, and to rinse off before/after with clean water to minimize the crud they bring in. People have enjoyed mineral hot springs for millenia, and the riverbed swimming holes where hot springs mix with cold. So the approach on this might just be to go for a level of sanitation that the current users can live with, and not worry about matching the level of sterilization that's needed for a public pool full of physical therapy patients and incontinent children. If someone on the lab wants to use it, and has a compromised immune system or concerns about santitation, then the tub should be scrubbed down immediately prior to their use, and refilled with clean water.

Last I checked, there was a smaller fire truck (brush engine) currently being used for non-potable water transport on the labs. Most of the current fire suppressants are chosen for biocompatibility - they are intended to serve as fertilizer in the forest as they break down. Most are similar to detergents. And you can see if there's a lot in the tank because it will suds or foam. foam should not be in the tank anyway, it's added to the hose after the water is pumped out of the tank.Most of the water being loaded in that truck comes from the creek or from a well. So it is being rinsed regularly, and by the time the hot tub is done I would not be worried about prior contamination from firefighting materials.

If you would not go swimming in the creek, the water should not be used for the hot tub either. I would probably ask them to fill up from the well if possible, if we were planning ahead for the hot tub session, just to keep things cleaner and crawdad-free.

As for BTU content - thanks again for the fuel numbers on your existing hot tubs / soaking tub projects. Natural gas / propane seems to have about 21,600 BTU/lb, or 47500/kilo. So if you're using around 5 kilos or 20 lbs of propane, then we're looking at 240,000 to 450,000 BTUs. 30 to 65 lbs of wood. Much better than the hundreds of pounds I was thinking! So insulation is key. A propane option would also allow firing the hot tub during our summer burn ban season, when solid-fueled outdoor fires are prohibited due to fire danger.

I am definitely interested in prototyping an immersion heater that achieves efficient contact with the water, yet does not cool the fire down to the point where it burns smoky and dirty (and inefficiently). That's version no. 1 for heating this thing. I like the Kelly Kettle idea too, and the idea of a side heater. I'm not sold on the mass-storage for a portable hot tub, though I can see the benefit for a permanent installation. If anything I might consider a solar pre-heater where the solar fluid served as mass to boost or pre-heat the water.

Thanks again for the good ideas, and especially for the benefit of your experience from those who've tried it before.

Now, can I see a show of interest in assembling the hot tub structure at Wheaton Labs?

yours,
Erica

Another thing to consider that erica reminded me of: To fit in with the standards at Wheaton Labs it would probably be made from wood, but other food-grade non-toxic or natural materials could be considered. Due to our current lack of a good water source up on the Lab, we need it to be skiddable or portable. Those are our only constraints.

Not to hi-jack this thread, maybe consider a rocket sauna instead. It could be a skid-able wood building you just have to figure out a way to have the riser inside of it.

Could water sanitation be assisted by pumping the water past strong UV lights? I've heard of this being used in addition to filtration to lower the use of chlorine in pools. I've not done much research into the subject as my hot tub project is rather far down my list. Here's some basic info I found on the subject from googling a bit. Using UV For Sanitation

Oooo I'm interested- 'twould be a great opportunity to work with Erica!
However, to get to Wheaton Labs and build it before October is a tight call. :(
I don't think it's possible for me, but lucky is the person who gets their hands on this project.

How about something like this? http://www.hydrohammock.com/

It meets the 'portable' criteria.

Sadly, I too cannot make it there to help with any build.

Thanks for the encouragement, Olenka!
It's definitely a bit of work, that's why we're discussing it here. If enough people are interested and willing to help, it can happen.

-Erica

I love the idea and SOOO wish I could make a trip out there to help, but there's just no way. Why didn't Paul set up somewhere in new england, dammit!

Will be watching progress on things best I can.

A thought occurred to me just now while looking at pricing for a pre-fab wooden cooper-style barrel tub to see what you might be facing going that direction (prices are in the thousands, of course)....what about a really big log chainsawed into a tub? I'm reminded of one of the old american indian techniques for making a boat/canoe where you literally cut down a huge tree and burn/chip-out a large cavity in the resulting thick "log". Something like this might work pretty well...would sort of create a long row of seats and if done twice over, would allow for one facing the other. This would have to be done with a decently rot-resistant and water-tight type of wood, such as cedar, of course. Just a thought that came to mind and didn't really spend much time on filling out the idea, but something like this might be workable on-site in a pretty short time.

...something like this but longer (and more rough / less "finished"): http://amusingfeed.com/15-creative-ways-to-adjoin-logs-in-your-home-decoration/#attachment_253

If you think cedar barrel tubs are expensive, try sourcing one of the few remaining cedar old-growth logs big enough to seat people in.
A Native American boat-builder friend, with access to tribal resources not shared with the rest of us, had to make do with a heart-rotted log for his latest project and fill in the rotted section. (And that's for a boat that seats people single-file, not immersion style.)
He was skilled enough to stretch it anyway, but there's a TON of work and skill, and a lot of wasted wood, that goes into authentic carved-out-log boats.
It's a lovely craft, and a lovely thought, but not a cheap alternative.

-Erica

The function of a rocket heater instead of a snorkel heater would be two fold:


1) less smoke. We would make the fire and smoke hotter before we start to extract the heat

2) extract more heat. We want to pull as much heat out of it as we can. We might be able to get ten times more heat from the same wood.



- - -

When it comes to hot tub stuff - this isn't really a passion of mine. It seems everybody else in the world LOVES hot tubs and I tend to spend my time elsewhere. So I'm not really bonkers about creating a hot tub. Other than people like it and I suppose it would be an overall plus to the empire.

So when it comes to getting involved in the design, I find my brain wanting to focus on other projects.

- - -

When it comes to preheating the water, what about our stuff about compost piles?

- - -

Maybe we need to put something together that is a bit like a kickstarter. The only issue is that people won't really get artifacts from this. Unless, of course, they want to build their own and see what we came up with. Or, maybe they want a weekend for two in the tipi plus use of the hottub. Maybe that's the way to do it: park the hot tub next to the tipi and people can have a weekend of hot tubbing and permaculture.

Because then we could just order up one of the pre-made tubs here: http://snorkel.com/hot-tub-products/wood-fired-hot-tubs.php

Click thumbs up on this post if you would be willing to shell out something like $300 for two nights in the tipi plus the hot tub for personal use.

When I click on your email link I am taken to the last post in the topic and need to scroll to the top to sign in. Then I'm taken to the list of topics so need to go back to email and click the link again. Irritating.

I only get to town twice annually (15 miles) so it's unlikely that I'll get to Oregon from Florida.