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Do you like keeping warm? Do you like doing so in hot tubs? If so; this might be the Instructable for you!

I will detail how my friends and I designed and built a wood-fired hillbilly hot tub that reached 112 degrees (F) within an afternoon using items from my local Home Depot!

Step 1: Building the Frame

To make this tub easy to set up and tear down, we decided to use a combination of old railroad ties and fallen logs that I had laying around for the frame. It is important to grade the ground underneath and check for anything sharp that could puncture the tarp.

We simply used twine to lash the logs together at the corners to prevent them from moving too much.

We placed bricks and other stones around the bottom layer to prevent the tarp from bulging out into the gaps left by the log-cabin style construction.

Step 2: Building the Heating Coils

This was the most expensive part of the hottub: using 35 feet of 1/2" diameter copper tubing to make the coils. Onto each end of the coil, I soldered a 2 foot straight copper extension to get out away from the fire, and to have a cooler area to attach the vinyl tubing for the pump.

The pump is a submersible 250 gph pump that I found at Home Depot. Do note that a pump such as this is much less expensive from Amazon, so I would recommend getting one there instead.

If you are iffy on soldering the copper together, remind yourself how with this instructable:

https://www.instructables.com/id/How-to-Sweat-solder-Copper-Pipe/

Step 3: Heating the Tub

This step can take awhile. You'll want to fill the tarp with water: we have done it with both pond water and city water from a garden hose, it really doesn't matter: you won't notice the difference, I promise.

I recommend using bricks or some other weight to hold the tarp up at first: we tied it using twine and the weight of the water ended up ripping the eyelets out of the tarp. Using weights allowed the tarp to be adjusted as it is filled. Once the water is in, it shouldn't move around too much.

Once it's full, start a large fire and the pump. Depending on how hot your fire is, this can take different amounts of time: in my experience, around 3-4 hours to achieve hot tub status.

One thing we did to speed it up was attach a steel pipe to the end of a vacuum on "blow" and stick it in the fire. The oxygen being shot directly into the fire really got it cooking.

One suggestion I would make would be to place the hot tub a bit further from the fire, and account for the wind direction that day. Depending on wind, you can end up with a lot of smoke and ash blowing right towards the tub, making for a poor experience. By making the vinyl hoses longer, the tub could also be moved further away from the fire.

NOTE: If the copper coils are in the fire, you need to have the pump running and water going through it, or else your solder will melt.

Step 4: Happy Hot Tubbing!

Good luck with your hot tubbing adventure! Also, Here is a parts list compiled:
(I spent a total of about $250 on these parts, but you could probably spend a lot less if you were thrifty about it)

30-40 feet 1/2" diameter copper coil

2 foot straight copper tubes (1/2" diameter) X2

2X 1/2" copper couplings

10 feet of braided vinyl

250 GPH submersible fountain pump

2X hose clamps (3/4")

Acid core soldier

Flux

Blowtorch

Twine

Bricks/stones

Logs, railroad ties, or a big hole

Large Tarp (big enough to fit your tub size of choice)

Water

Fire

Shop vac or leaf blower with a metal tube at the end to stick into the fire (optional)

<p>suiterelliot, Fire, earth, air, and water -- the Brave the Elements Contest is about all the things you make and do to withstand or take advantage of the elements. Your project involved all four elements. You used a fire pit, a vacuum as a wind turbine, pond water which is a combination of a rain collection systems and earth collection system, and you used logs which are part of the earth. You and your friends were able to harnesses the power of nature heating water with fire and you did it when there was snow on the grown. Your project hit all the areas of the contest and it was easy to follow your instructions both with the pictures and the writing. Well done and good luck in the contest.</p>
<p>Gee just what I want a hot tub full of guys!! </p>
And your point is what?
<p>That he's being sardonic or serious.</p><p>Is it that tough to suss?</p>
<p>rather than spending $$ on copper a salvaged car radiator works....while yer at it grab the water pump and the whole thing will run off a car battery. there's also this: http://thehomesteadsurvival.com/build-5-gallon-bucket-sink-diy-project/ home made foot pump can be operated under water</p>
<p>Would the radiator stand up to flame heat??</p>
<p>there are several folks demonstrating this technique on the web. youtube etc. google hot tub car radiator...of course you wouldn't want a plastic radiator (never heard of such a thing, how does it conduct heat?)</p>
With most car radiators now adays being aluminum and plastic, I doubt see that being a solution. Also every production car I've ever worked on uses the engine to drive the water pump not a separate electric motor. You can however buy one for racing applications which would most likely cost more than what the author of this article spent on the entire project.
<p>Move the pump outside (a 12V bilge pump would be safer)</p>
<p>Oh I fergit, coroplast is available free after most election cycles. big political signs made of it they do not rot or get mushy. And after a nasty election cycle AFTER it is done go out and harvest away, as most politico's leave their crap laying around forever. </p>
<p>Check with your local municipality, but most places consider them &quot;Unclaimed Trash&quot; even during election season... I used to make airplanes out of them back in the day.</p>
<p>Not to seem a spoil sport but based on my time in Japan you can make a hot tub with a stock tank and a terra cotta U pipe. The U pipe is mounted in vertically in holes in the stock tank with the protruding portion going into a firebox with the water flowing through it. Convection from the fire heat causes the water to circulate and the tub gets warm.</p>
<p>I would have second thoughts about a power cord in the water with me, even if its meant to be.</p>
<p>Oh of you are al cherapo like me you could use layered corrigated cardboard to insulate the outer walls Just make pillows with plastic bags, and seal them from water. Can do the same with the floor.</p><p>sweet party trick!</p>
<p>I would suggest to add Styrofoam insulation sheets to the bottom and sides of the hot tub (outside the tarp against the wood frame ) to make the bottom softer and smoother to sit on and the sides smooth and hold in some of the precious heated water longer. Another suggestion is to make stove out of a 55 gallon drum or 20 gallon grease drum ( like a burn barrel standing upright ) and put a short chimney on it to keep any smoke off you if the wind changes. </p>
<p>grest idea I was just about to say that! You make stadium seat, or winter camping hot seats out of foam. Ugly , but highly effective.</p>
well done I have always wanted to do this. Do you really need a pump I would think this would cycle itself with the incoming cool and outgoing hot?
Your coil would need to escalate upwards and the outlet would need to be higher than the inlet.
<p>There is definitely a way to get a cycle like that going, but for us, if the pump didn't run, the water didn't flow. </p>
<p>Couldn't it be somehow dangerous to have have of your body in hot water and the other half in freezing air (where there is snow)?</p><p>Anyway, I hope the cover picture/thumbnail was green screened (And I sadly know it wasn't...)</p>
<p>it's invigorating.</p>
<p>It is not dangerous. Hot tubs are very common and safe pieces of equipment, actually. </p>
<p>I'd be more concerned about the pond water. Heated water can breed bacteria. Better to start with good water since there's no filtration or added chemical sanitation.</p>
<p>No it's perfectly harmless and in fact is considered good for your circulation. Have a friend smack you with branches of eucalyptus. Happy Sweating!</p>
<p>sometimes you just got to be all dudes. Other times there's room for chicks.</p><p>Foxy chicks preferred.</p>
<p>I think this should be called &quot;Redneck Hot Tub&quot;. Of course, I'm from the midwest. Cute picture and lots of imagination.</p>
For comfort, find some old lawn furniture, drill the frame tubes at the top and bottom and let them fill with water. They won't last forever, but I get the feeling this is a temporary set up all around.
<p>It dose not look that hard</p>
<p>Awesome! For a more permentant solution, I might consider casting the the pit with the copper woven through the cement :)</p><p>I will probobly build one of these eventually!</p>
Very interesting design! How long did it take to build?<br><br>Have a great day! :-)
<p>From start to finish, it ended up taking about 2 days.</p>
<p>Looks like an awful lot of work. Try using bales of straw instead. Makes for softer sides and a nice place to sit all around. Use play sand for a soft tarp protective bottom. I'll leave the water heating method up to you though. Have fun!</p>
<p>There's an obvious lack of girls here !</p>
<p>Haven't you ever heard of &quot;no girls allowed&quot; :D</p>
super cool. I've always wanted to build a hot tub like this, but have the fire enclosed in a pit of some sort and the lines longer and insulated. <br><br>if it's close though you can stoke it without getting out.<br><br>
<p>Nice hot tub design. Did you have any problems with the plastic melting?</p>
Not from the water, but ashes that fell on on the tarp close to the fire did melt tiny holes.

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