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How to heat outdoor bathwater?

OK so I have created an outdoor bath area behind the shed and would like to hear best option for heating the water (from the water tank which is freezing). Was considering the Solar Dome for heating, also using black pvc pipe lining the roof of the 6 x 6 shed. Shed and tank get plenty of sun also.

Solar dome requires a pool pump, and black pvc pipe would also need some sort of pump. Have googled and there’s not a lot on this which is weird! Have access to electricity from the shed if a heat pump would be the best option…

Am happy to turn it into more of a spa set up instead of just filling it up and emptying it every time 😁

Picture for reference.

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Comments

MitchellMc

Hi @Dogdish28,

What sort of temperature are you hoping to achieve? Coiled poly pipe, or black PVC lining on the roof, will indeed help warm the water as it absorbs heat from the sun. However, it may not reach the high temperatures you’d expect for a comfortable bath. On a hot day, circulating the water through a black pipe could raise the temperature by a few degrees with each cycle, but it may need several rounds to reach a warm-to-hot level suitable for a relaxing soak.

If you're looking for a more spa-like experience with reliably heated water, you could consider installing a small heat pump. Since you have access to electricity from the shed, a heat pump could maintain the water at a steady temperature, even in cooler weather or after sundown. This option is also efficient and manageable if you plan to keep the water at bath-like temperatures for extended periods.

Alternatively, if you prefer to keep things solar-powered, you could pair the solar dome or black PVC coil setup with an efficient, insulated storage tank. By cycling the heated water into an insulated tank, you can preserve the temperature for longer. This could allow you to top up the bath with warmer water without relying solely on sun cycles.

Let me tag @Dave-1, @Noyade, @TedBear and @Nailbag to see if they have any thoughts.

Please let me know if you have any questions.

Mitchell

Dave-1

Good Morning @Dogdish28

🙂 I am currently in the process of building an outside area for a spa to be heated alternativly (other then from the power grid)

Some things you could have a look at are -

- A dutch Spa, no not what wentthrough your mind lol Its a coiled stainless steel pipe that you place a fire inside the coil to heat the water. As the pipe is spiraled the water is heated via convection. No pump needed. I was powering along towards this idea until I realised that radiant heat would be an issue. With a bathtub sized container the fire can therefore be less intense 🙂

- Reusing second hand solar panels (my current option) to then use whatever I get from the panels to heat the spa. Think of it as a big heat sink that will heat up all the time. Yes you will need to consider what happens when the water is emptied and to keep it clean. Diconection of the panels would work when not being used.

- For your instance a rocket stove would work well I think, minimal stove area, and heat can be extracted via a coil around the stove.

Dave

Nailbag

Hi @Dogdish28

Other than the terrific suggestions by @MitchellMc @my only other thought would be to research “portable camping hot water systems”. There is quite a range of products available with different power source options. A mate of mine recently added one to his off-road camper trailer that instantly heats water for a portable shower. I think it has the option of running from a gas bottle to.

There are also older style wood burning ones that you could use more easily accessible lump coal in.

Nailbag

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