DIY Hot Tub?

[The Accidental Mustachian]

So i'm thinking of knocking up a DIY hot tub.

Using

1000 lt. water storage container (the ones in the metal cage) top cut off. (£40)

Clad in wood from pallets. (Free £5 for some nice wood stain)

Water heated by a copper heat exchanger in a rocket type stove? Was hoping that this would work by natural syphoning process of hot water rising? (£40?) C'mon you smart engineers is this doable?

Something like this but i think i could possibly improve on the stove? https://www.youtube.com/watch?v=CMh_7ti8cuA
So I reckon i can do this for under £100. Wondered if anyone had done this? Advice on building the rocket stove would be appreciated. There are quite a few you tube vids of similar projects but you can't beat hands on advice!

[waffle]

Don't know about actually building a hot tub like that, but I can tell you that those plastic containers in the metal cage are fairly light sensitive and if left out in the sun will have a life of just a few years. Not a huge replacement cost, but possibly a big pain.

[Anomalous]

Sounds like an interesting project. I'd be very wary of a home made heat exchanger on a rocket stove though. I've looked into doing something similar before, and apparently it's very easy for things to go wrong and end up in a steam explosion.

I wonder if you could heat it up adequately using a solar water heater instead? I assume the tub would have to be well insulated. Here's a good site for DIY solar stuff, including plans for solar water heaters: http://www.builditsolar.com/Projects/WaterHeating/water_heating.htm

[paddedhat]

Sounds like an interesting project. I'd be very wary of a home made heat exchanger on a rocket stove though. I've looked into doing something similar before, and apparently it's very easy for things to go wrong and end up in a steam explosion.

My son was working for a fascinating guy who is a very eccentric tinker. At one point this guy blew a block wall over, in his shop, when he failed to honor the laws of thermodynamics. Fast forward to my son telling me that he is soldering up a "really cool" heat exchanger to heat domestic water, in the shop. This unit is going to be retrofitted to the hot air furnace. The first thing I ask is if he has a Pressure and Temperature relief valve in the system? "No, what's that?" was the reply.  I show him a Watts Regulator valve, and told  him to either add one, or stay far away from the first firing of this dubious device.

He was actually smart (scared?) enough to listen, and stood far away during initial testing. He also reported that the explosion was deafening, and that there was copper shrapnel everywhere.

[The Accidental Mustachian]

As it would be an unpressurised system that just loops though the heat exchanger from the bottom of the pool to return freeflow to the top of the pool im guessing that there is no chance of an explosion via a pressure build up??

Like this system here, once he has unplugged it from the water tank?

https://www.youtube.com/watch?v=5IRLVCJ1olA

[Anomalous]

I don't know much about heat exchangers. However, my understanding is that if water is heated in a small diameter copper tube, you can get some combination of steam bubbles and liquid water that will block the tube, and can then build up enough pressure to burst the copper.

I'd be comfortable with a home made heat exchanger in either of these two circumstances:
1) Temperature in tubing is never high enough to turn water into steam.
2) Water is heated in an open container with no way for pressure to build up. Hot water may be circulated through tubing, but never steam.

It's possible that I'm being overly conservative since I don't have a good grasp of the thermodynamics involved. Just be careful if you do try this.

[dess1313]

Have you ever seen a bale hot tub?  If you made it with  black plastic, it would absorb a lot of sun heat.  Then a urn of some sort that you can make a fire in would work.   See the links

I have also used the electric heaters for cattle water troughs for winter, otherwise the water troughs turn into frozen blocks and cows get no water.  a small one kept my fish pond from going to ice during the early spring and late fall.  If you left a big one of those in over night, it would be nicely heated by the next day. 

Although since you're mixing electric with water, i would not leave it in/running while using the hot tub and be very careful of your electrical cords and such.  Put a guard around the heater so you can't accidentally touch it while in the water.  You can burn yourself on it.  A metal pail with large holes does well usually and kept my fish from getting hurt

[daverobev]

You know the guy from Grand Designs?

https://www.youtube.com/watch?v=QhhIc_uG4Zk

[Kaplin261]

Consider the time needed to make this work, now add in the dangers of thermodynamics. Now go on craigslist and do a search for a real hotub. People praticly give them away once they start to age and begin to have problems.

With a pressure washer and a little bit of tinkering you could have the real deal in your backyard for under $250. But your going to need a electrical outlet and concrete slab.

[amandapdx]

If you're having trouble with heating the water, you can always consider buying a heating coil from The Original Nomad here: http://theoriginalnomad.com/collections/nomad-travelling-soaking-tub/products/coil
A bit more money but you can use a variety of fuels and it potentially fits most hot tubs, and not just their own.