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Small Cabin Forum / Member's Projects and Photos / Off Grid Hot Tub
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littlesalmon4
Member
# Posted: 12 May 2017 16:56 - Edited by: littlesalmon4
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550 gallons. Takes about 6 hrs to heat water from 0 c to 39 c.
After that only an arm load of wood a day to maintain temps.

razmichael
Member
# Posted: 13 May 2017 10:55
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What a great project! The rubbermaid livestock tubs are robust and can handle some water freeze but can also crack. I have three or four sitting around that I need to figure a good way to patch as they have cracked over winter (used with horses). The 'drain plugs' and treads can also get damaged if constantly removed so, if you plan to draining through this, I suggest you permanently attach a draining hose of some type with a valve rather than plan on removing the plug each time.

Curiosity only - did you considered a closed heating system with a heat exchanger in the tub so you could use an antifreeze? Common technique for DIY solar water heating. Some loss on efficiency but less freezing issues.
Wonder how much electricity you could generate using a thermal generator on the heater, small battery and small pump (perhaps also with a small panel) to pump the water through the boiler? - project for another day perhaps.

ForceFed70
Member
# Posted: 13 May 2017 13:09
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Thanks razmichael. Really appreciate the suggestions!

I plan to drain the tub between visits, and yes I'll attach a permanent pipe with drain valve. You can see the pipe with valve on that last pick of the mock-up. The lower pipe goes to the boiler where it Y's off to a drain valve. Draining the tub and boiler will just be a matter of opening a 3/4" valve and waiting.

I did consider a closed loop system as you describe. But it was going to add significant complexity to the build and I was worried it might impact the thermosiphon effect. I'm already concerned that at full flame the water may not circulate quickly enough causing boiling/steam in the boiler.

I'll have to figure out a pump system if thermosiphon isn't enough. Those thermal generators would be perfect but really pricy! I'd probably just get the smallest 12V pump I can get away with and attach it to the cabin's small 12V solar system. Beef up the cabin power system if I need to rather than something separate for the pump.

razmichael
Member
# Posted: 13 May 2017 16:33
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Quoting: ForceFed70
I'd probably just get the smallest 12V pump I can get away with and attach it to the cabin's small 12V solar system.

Although you can DIY a thermal electric generator relatively cheaply, using the existing power would make the most sense if you are close enough to the cabin (voltage drop not an issue). Lots of inexpensive hot water 12v pumps available that do not draw much power - naturally that statement's accuracy depends on how much power you have! Always add a TEG in later to augment the power to a pump - just another fun project! Hopefully you will not need a pump (just make sure you don;t end up blowing up the pipes from too much heat/steam).

ForceFed70
Member
# Posted: 30 May 2017 00:08
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Spring has finally sprung! Spent a few days on the project.

1st step was building the water system for the cabin. The idea being that it would be this same system that's used to fill the tub. Everything worked out great. The design is pretty simple. Oldschool gas powered briggs and stratton water pump, 1.5" water line, and a 50 gallon barrel on the roof (sorta). There is a T in the line that will be used to fill the tub. Very pleased with the results, gravity fed water is ample flow (careful consideration into fixtures and plumbing used to maximize flow with low pressure) and the barrel fills in only a few minutes.
Water_System.jpg
Water_System.jpg


ForceFed70
Member
# Posted: 30 May 2017 00:09
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--------------------------------------------------------------------------------

Here's a pic of the pump. Well, not really, it's a pic of the pump enclosure with the lines running to/from the pump. Forgot to snap a pic with the cover removed.

It's just some pressure treated lumber and a rubermaid tub as a cover.
Water_Pump.jpg
Water_Pump.jpg


ForceFed70
Member
# Posted: 30 May 2017 00:11
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Also got the decking built. Nothing fancy here. Pressure treated lumber and lots of deck blocks to handle the weight.

Smallest shop foreman and SWMBO approved!
Tub_decking.jpg
Tub_decking.jpg


hct4all
Member
# Posted: 20 Sep 2017 21:11
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Any update s

Salty Craig
Member
# Posted: 21 Sep 2017 21:32
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ForceFed70

I bought the same tank this summer with identical ambitions. Love your build. Thanks for all the helpful insight.

We used it for a swimming pool this summer. See pic. I can't wait for Gary O to make a wisecrack!!
Come on in, the waters fine
Come on in, the waters fine


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