Introduction: Off Grid Japanese Soaking Tub

This is an ongoing project I am working on so feel free to offer suggestions in the comments!

The story so far:

I live off grid in a small cabin using solar and wind power and I wanted to have a greenhouse for starting plants in spring and a place for a small hot tub and to store my riding mower and tools in winter.

Step 1 was to get a greenhouse and I found one that is 7x15 for $115. It would have cost me more to build one that size so I chose to go the easy route and it looks and works well. You can also build your own and cattle panel and hoop house greenhouse plans are on Instructable and youtube.

The project will be using mostly renewable energy from the sun but will include thermal mass storage, solar water heating and either wood burning or a small propane heater in the project.

I am using a recycled cattle tank made by Rubbermaid for the hot tub because it is just the right size at 70 gallons for one person and it has a drain plug and will hold up for a lifetime of use.

I recycled my small pool filter pump to circulate the water in the tub and I am using a 12 volt Shurflo 3.5 GPM pump and an Eccotemp L5 On Demand propane water heater to bring the tub up to 100-104 degrees. The water pump and pool filter pump are run off a 100 watt solar panel and small inverter.

The greenhouse gets to about 100 degrees when the outside temperature is 70 degrees and that heats the tub up to between 75-80 degrees. So it is being passively heated which means I only need to heat it a little more to reach hot tub temperature.

I can heat the tub using the Eccotemp for just a few pennies in propane in 20 minutes. Yes I know propane is not considered renewable however, propane is a waste gas and bi-product of natural gas and oil drilling and if not used it would have to be flared off. The Eccotemp is very efficient at about 99%.

I also have a clear plastic cover for the hot tub which holds the heat in and reduces evaporation and a thermal blanket to cover the tub at night which reduces heat loss.

I will also be installing a solar water heater that uses black plastic tubing as I progress on this project and my hope is I can heat the tub with only passive solar energy on sunny days and just use the OD water heater on cold sunless days.

ADDITIONAL BENEFITS:

The tub acts as thermal mass and also increases humidity in the greenhouse so it helps to balance the temperature in the greenhouse and it does not get outrageously hot in summer. The tub releases heat at night and it helps keep the greenhouse warmer and more humid so plants thrive.

Enjoy the video and please VOTE on the orange tab and leave feedback and suggestions in the comments!

Materials:

1) stock tank 70 gallon or similar tank that suits you

1) 12 volt shurflo pump 3.5 GPM or similar

1) Eccotemp L5 OD water heater or other heating device- wood, solar or 12 volt element?

1) 80 or 100 watt solar panel

1) 12 volt battery and deep cycle preferred

OPTIONAL:

Small pool filter pump

Comments

author
LaMar Solarcabin (author)2016-06-21

Update: I made a simple solar water heater for the hot tub out of a coil of black irrigation pipe and a small 12 volt DC pump and solar panel. That is what I use on sunny summer days to heat the tub and no propane needed. It raised the temp from 70 degrees to 110 degrees in about 6 hours with the tub in a greenhouse. https://youtu.be/dY4inDXOQg8

author
LaMar Solarcabin (author)2016-06-03

Here is an update of my greenhouse spa and Japanese cottage design ideas. I finished the greenhouse plant rack and built a nice Japanese garden bench. Also plans for my dry pond and foot bridge: https://youtu.be/k7Xgf0umuOw

author
andrefierens made it! (author)2017-02-26

Thank You ! Nice project !

Instead of the garden hose I use now a Solar Mat from Intex.

And a SolarMax 600 ( Pump and photovoltaic Panel 12 Volt )

which makes the system Portable !

https://www.instructables.com/id/Portable-Solar-Po...

http://www.metric-conversions.org/

tenerife test.JPG
author
Homeofmyown (author)2016-11-05

You might try a submersible 12 volt stock tank warmer, available on Amazon. They are used to keep cattle water tanks from freezing over. I'm thinking it would cut down on the amount of propane use and time to bring water up to temperature.

author
UpYourSolar (author)2016-07-07

Oh Yeah...this looks great! Congrats on the solar water heater addition. We have a 26 ft diameter dome greenhouse with a 1,500 gallon watertank/fish pond inside that works on the passive solar principals you mentioned. Here is something to consider based on our experience: Convert the greenhouse idea into a sauna :) Temps 95 and over will generally not promote plant growth. Pavers on the ground will enhance the heat gathering capability as well as slowly release the heat at night to help regulate huge temp swings. Same principle as Trombe walls. Convert your plant shelf idea to sauna benches. Best Wishes & Keep on Creating! Jill

author

Thanks Jill- I use the greenhouse primarily for starting plants/seedlings in spring and prolonging the season for fall plants. In summer it is used for a spa and in winter will be used for storage of my lawn tractor and gardening tools. We get very cold winters here but summers are not too bad. I am very happy with the greenhouse and hot tub has sure been nice and used a lot. Have been heating it with just solar for months now.

author

Ah Ha! Perfect

author
UpYourSolar (author)2016-07-07

Oh Yeah...this looks great! Congrats on the solar water heater addition. We have a 26 ft diameter dome greenhouse with a 1,500 gallon watertank/fish pond inside that works on the passive solar principals you mentioned. Here is something to consider based on our experience: Convert the greenhouse idea into a sauna :) Temps 95 and over will generally not promote plant growth. Pavers on the ground will enhance the heat gathering capability as well as slowly release the heat at night to help regulate huge temp swings. Same principle as Trombe walls. Convert your plant shelf idea to sauna benches. Best Wishes & Keep on Creating! Jill

author
tn. (author)2016-06-12

this is brilliant. my dad is 74 and mobility-impaired. he lives in a little country house that, well... let's just say the general consensus is that a match is the kindest thing that could happen to it. it takes him nearly 3hrs to get to the nearest grocery on his mobility scooter, so there's not a lot of fresh produce in his diet and, at his age with his medical conditions, he really needs it. the house also has no running water - he throws a sump pump in the river and fills up barrels inside the house which means the overall scent is that of moss and mold. it also means no personal hygiene for the weeks and months he lives there until he's dragged, kicking and screaming, back to civilization for a hose-down.

i am definitely saving this in favourites and will be implementing it asap.

author
tn. (author)tn.2016-06-12

oh - one question: i'm not up on my temps - is the water tolerable without the extra heating? also, what is the disinfecting routine? is regular ol' chlorine okay to use?

author
LaMar Solarcabin (author)tn.2016-06-12

It will need some extra heat source but that could be as simple as heating a bucket of water on the stove and adding that to the tub. Most people like the temp around 100 degrees to soak. Be careful not to scald anyone.

author
tn. (author)LaMar Solarcabin2016-06-12

that's the concern - he heats with a wooden stove but he cannot manage it any more (especially not after someone walked away with just on a bush cord - enough to heat for three months). because of balance issues, i don't like his using the wood stove, which is why i've started researching safer alternatives (such as an induction burner to cook with - can't burn himself on it if he gets wobbly and plants a hand on it).

i think i'll toss up a coil of black pipe on the rooftop (which is sheet metal) and use that to bring the temp up.

author
imjustgrandma (author)2016-06-05

You could add a lot of large rocks when it is cold to soak up sunlight heat and release it at night.

author

Thanks friend- I have thick patio block on half of the floor where the tub sits and that is thermal mass that absorbs heat and releases it at night. I may add more rock in corners as I progress.

author
LaMar Solarcabin (author)2016-06-05

Update 6/5/2016: Outside temp reached 82 yesterday and even with the greenhouse doors and vents open the hot tub reached 95 degrees just covered with some clear plastic. Only ran the Eccotemp for about 10 minutes to bring the water up to 105 degrees. That is really reducing any use of outside heat and water warmed by the sun is the best!

author
yizahkJamesLafter (author)2016-06-03

great project, have just gotten what to do with my small piece of land. i will definitely try it out. GREAT PROJECT

author

Thanks friend!

author
LaMar Solarcabin (author)2016-05-30

This is an ongoing project and experiment to use renewable energy to heat a small hot tub and use that thermal mass to help keep the greenhouse warm at night and add humidity so plants thrive.

I will be using several methods of heating and heat storage as I progress and if you have ideas please share them in the comments. I will update as I progress.

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Bio: I am a long time off-grid homesteader and I live year round in a solar cabin I designed and built myself. I use solar and ... More »
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