Case Study: Francisco’s “Fire Pit” DIY Hot Tub Build (Chile)

Last updated: September 2026

Some projects are just that bit different, and this is one of them. Francisco, in Chile, wasn’t content with a “regular” DIY hot tub. He wanted to heat it with a fire pit.

Background

Francisco got in touch because he wanted to do something a little different with his DIY hot tub build. The idea was that the tub would be heated mainly by a custom-made fire pit and heating coil placed next to it, with electric heating as a backup.

It was certainly going to be an interesting project. If you like the idea of fire-heated water, have a look at my off-grid wood-fired hot tub review and Off-grid hot tub: luxury in the wild or impossible dream?

Scope of work

Francisco asked me to do a custom design for the project. I also supplied all the parts and exported them to Chile, as he was struggling to find them locally.

One thing to note: getting hold of imperial-sized pipe in Chile was a challenge, to say the least. So Francisco had to import a lot of metric-to-imperial converters for the plumbing. And the last thing you want to do is export pipe. It’s big, heavy and costs the earth to ship, so wherever possible, locally sourced pipe is the best option.

If you’re building outside the UK or USA, work out early which pipe standard your local suppliers stock, and design around it. I’ve covered pipe sizes and types in Hot tub pipe: the ultimate guide. Many pool fittings also work on a hot tub (see Can I use pool parts on a hot tub?).

The design

Like many projects, the design changed as it went along. Where we started with Francisco’s design isn’t where he ended up. He totally changed the shape and size of the hot tub, and that’s absolutely fine. It’s exactly how things should be when the customer, like Francisco, decides to do it.

The point is that the documentation and knowledge I gave Francisco let him make the changes to the design himself, once he fully understood how everything works and fits together. We started with a more conventional square hot tub, and it became the more contemporary triangular design you can see in the videos below.

If you’re curious about how a custom design comes together, I’ve explained it in Custom designed hot tub: the process explained. For the thinking behind a good layout, see What makes a good DIY hot tub design?

Building commences: November 2021

Here’s Francisco’s build in his own videos.

Thinking about a fire-heated hot tub?

Francisco’s heating was custom-made for his build. If you’re considering something similar, here are a few general points to get right:

• Keep plastic pipe away from the heat. Standard PVC is rated to a maximum operating temperature of 140°F (60°C), so the part in or near the fire must be metal (copper or stainless steel), with PVC only once the water has cooled.
• Never let the coil be isolated while the fire’s lit. Water trapped in a coil over a fire can boil and build pressure. Water must always be able to flow through the coil and back to the tub.
• Keep an electric backup, as Francisco did, for the days you don’t want to light a fire.
• Watch the temperature. A fire doesn’t have a thermostat, so check the water before you get in.

For all the heating options side by side, see What is the best method to heat my DIY hot tub?

Planning something a bit different?

If your idea doesn’t fit a standard box (an unusual shape, an unusual heat source, or a build abroad), start by sketching it in the free Tub & Pool Designer Pro software. I can then turn it into architectural CAD and a 3D plumbing design. If a standard size suits you, my DIY hot tub plans come in imperial and metric, with CAD drawings, the plumbing layout, a parts list and the video course.

What do you think of Francisco’s fire pit idea? Let me know in the comments below. I read them all.

Cheers,
Andi

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Thanks - Andi

 

Hi, Andi here. I own Buildahottub.com and also write all of the articles and info pages on the site. Some years back now, I built my own hot tub but struggled to find the information I needed. So, once my tub was complete, I started this website to help others in their own pursuit of hot tub and plunge pools DIY building information.

Fast forward to 2025, I've helped over 1400+ DIY customers just like you all over the world build hot tubs and pools. Have a good look around the site, there are lots of resources here. Please do get in touch if I can help you. - Cheers, Andi