Adding a Hot Tub to a Pool: Scott’s DIY Build in Arizona (Case Study)

Last updated: September 2026

Scott, from Arizona, USA, first got in touch with me in May 2022. He was looking to add a hot tub to his pool. After putting out feelers to see what a builder would charge, Scott decided that, with my advice and guidance, it was something he could do himself. It would be a fun project with his son, and most importantly, he’d save a whole bunch of money in the process.

Fast forward to January 2023, and Scott was almost ready to start. He hired me to design a custom layout for his hot tub that would use the heating and filtration from his existing pool, but with separately controlled jets.

The plan

Here’s what Scott set out to build.

What Scott is excellent at is planning. He plans everything to the absolute nth degree, and that’s really helpful on a project like this. He also likes to understand everything in complete detail before he starts, which is another great trait when you’re taking on a build like this.

If you’re thinking about the same kind of project, Can I add a hot tub to my existing swimming pool? and Hot tub pool combo: the complete DIY design guide cover the options.

Scott’s first step was to mark out the area for the tub and try it for size. Again: planning, planning and more planning.

Let the hard work begin

Time stops for no one, and we were now into the summer months in Arizona. As I’m sure you can imagine, it’s hot, and then very hot. What better way to spend your summer vacation than getting roped in by your dad to dig a hole for a new hot tub?

It was back-breaking work, but Scott’s son got stuck in.

You have to remember just how dry and hard the ground was. Not being a total slave driver (lol), Scott got some very welcome help in the form of a digger. That made life a lot easier!

When you’re digging the hole, remember that you’ve not only got the roughly 43in of depth for the hot tub itself, but a further 6–10in for the base. That’s a deep hole, and a hard one to dig by hand. There’s more on working out the depth in How to build a DIY in-ground hot tub.

Trying it for size

As you’d expect from Scott, he wasn’t going to go blindly into laying blocks. He wanted to dry-lay them first, so he set out the shape he was going to build to try it for size. Planning, planning and more planning. Fantastic.

Time for a vacation

At this point it was time for Scott and the family to head off on their summer vacation. You’d expect some good old-fashioned R&R, but not for Scott. He was still thinking about and planning his tub.

It helped that one of the pools where he was staying was being refurbished, which fuelled his curiosity. And of course, he took the planning document I’d written for him during the design phase as some holiday reading. He was even emailing me questions from the sun lounger. That’s keen, Scott!

The practice run

Back from vacation, Scott and his son turned their attention to the existing pool pad. The plan was to modify the plumbing and “hijack” one of the existing pool returns, sending it to the hot tub to create an overflow.

This was also a chance to practise their concrete work, because they needed to pour a larger pad. Nice work, gents!

That went well, so the next step was to pour the base of the tub. “No going back now” was the email I got from Scott at this point. Well, he could always put all that rubble back in the hole, but I’m sure his son would have something to say about that!

All hands on deck: time to mix some concrete.

Before you pour a base, it’s always a good idea to lay a liner to stop dirty water getting in. Some people don’t bother, but I tend to. (One YouTube commenter once accused me of single-handedly destroying the planet with single-use plastics. For the record, I do recycle.) My concrete slab guide has more on bases.

If you’re fitting pool-style main drains in the floor (the flat ones at the bottom), now’s the time to set them in place. They’re great for circulation. If a jet pump will draw through them too, check the covers are rated for that pump’s flow, and fit two drains at least 3ft (1m) apart with anti-entrapment covers. In the USA, drain covers must meet the Virginia Graeme Baker Act standard. There’s more in Installing a main drain.

Nice work, gentlemen. This is coming along really nicely.

Pad done, time for some walls

Would you believe it, we were now into December 2023. While most of the Northern Hemisphere had stopped building because it was too cold, Scott, his son and the wonderful Arizona climate were cracking on.

With the base in, it was time for the walls. Scott used hollow 8in CMU blocks, which he’d reinforce with rebar and fill with concrete once the plumbing was in place. They’re cheap and very strong. Apart from having to core holes in them for the plumbing, which isn’t a big deal, they’re a great material to work with. See Cinder block hot tub: a DIYer’s guide and my rebar guide.

Here’s where things stood on 13 December 2023. The lower two and a half courses of block were in for the footwell. The next steps were the concrete pour for the seats, followed by the retaining exterior walls.

Time for some pipework

Next, Scott started on the plumbing. This wasn’t going to be straightforward, as there were several changes we’d planned:

• New pipe runs for the hot tub jets.
• Pipe runs for the hot tub circulation pump, so the tub’s water could be heated and filtered separately.
• Runs for the waterfall. We were hijacking one of the existing pool returns to deliver pool water into the hot tub. Putting in more water than the tub can hold makes it overflow, which gives the waterfall.

The waterfall is on a diverter valve, so it can be turned off when you’re heating the tub. The last thing you want is to pour cold pool water into a hot tub you’re trying to heat. That would be totally counterproductive. I explain why I usually keep the waters separate in Pool and hot tub plumbing: why they should stay separate.

Scott ran the pipes from his control room to the new tub and insulated them to protect them from freezing on cold Arizona winter nights.

Jets

Scott also needed to get the jets in at this stage. That meant coring holes through the walls and then cementing the pipes back in so they’re watertight. It’s an involved process, for sure. I’ve covered it step by step in How to install gunite jet bodies in a DIY hot tub.

Render and waterproofing

With the jets in, it was time to render the walls and then apply the waterproofing. Scott used a waterproof render mix, which is regular render with an additive that reduces the amount of air in the mix. The blocks themselves are porous, so they need sealing.

Once the render is on, you can waterproof the surface. There’s no shortage of brands, including Ardex, Laticrete and Mapei. Any product made and approved for pools will be fine. Follow the data sheet for primers and coats. My waterproofing, tile adhesive and grout guide has more detail.

Water testing

Scott’s big worry was that his tub would leak. I’ll be honest, that’s the biggest worry for most DIYers. The challenge is that a proper pressure test of the pipework is hard for a DIYer. It needs a lot of kit most of us don’t have lying around in the garage, and you’d also have to cap off the 2.5in gunite pipes.

The alternative is a water test. Fill the tub, close off the plumbing and look for leaks. You’re watching for the water level dropping overnight, and you can inspect the pipework and the tub by eye.

It isn’t the same as water under pressure. When Scott connects the pumps, the water will be under pressure, so he could still find leaks then. That’s not easy to test for in advance.

I always say, if you have any doubt that you’ve made a joint correctly, or you had to force it into the fitting, it’s going to leak. Cut it out and do it again. There are no shortcuts to a good plumbing joint, and well-made joints don’t leak. See How to make the perfect PVC solvent weld joint and, if you do find a leak, Hot tub leak? How to find and fix it.

Scott found that the seal around one of the jets was leaking, which he was able to seal. That was all he found, which was a relief.

Control room remodel

Adding a hot tub to the pool meant some additions to the pool pad, or control room. The tub needed its own filtration and heating, a new jet pump and a spa pack. All the pumps are self-priming, because the pad is above the water line. Scott’s setup has a 3HP BLACK+DECKER pump and a Hayward circulation pump, with the filter and the spa pack placed alongside. For more on this, see What are the self-priming hot tub pump options? and Hot tub control room design considerations.

We also needed to change the pool plumbing to divert the pool return we’d hijacked for the waterfall overflow.

It all sounds more complicated than it is. Scott was, of course, following the plan I drew up for him.

The electrics

With all the new kit, the electrics needed changing. I must stress that all electrical changes should be done by a qualified electrician.

Adding a new heater, two new pumps and some new lighting was going to increase the current draw on the main pool breaker box by about 60A. We needed to make sure there was enough “juice” for all of it, as the existing pool kit was on much smaller breakers. Scott needed to reroute some cables and increase the circuit amperage.

A qualified electrician will also advise on cable sizes. You can’t just push 60A through a cable designed for 15A, for example. It would get hot and could melt, trip breakers or even start a fire.

Wiring and programming the spa pack

Normally, the plumbing is the trickier part of a DIY hot tub build, but for Scott it was the electrics. The biggest challenge was working out the wiring for the new spa pack.

In the USA, spa packs run on a 240V supply with two hot legs, a neutral and a ground. Some parts of the pack run at 240V across both legs and others at 120V from one leg to neutral, and Scott had trouble working out the terminal connections. Unlike most household wiring, you’ve got different voltages on different terminals, which can be hard to get your head around the first time. I have the same conversations with electricians doing hot tub installs as I do with DIYers, so Scott was in good company! My hot tub wiring guide and Demystifying spa pack wiring diagrams go through it.

The other challenge was programming the spa pack. It has to be set up to recognise the equipment connected to it, or it won’t work properly. For example, if the air blower isn’t set up correctly, it won’t turn on. There’s a walkthrough in How to configure a Balboa spa pack.

It’s incredibly frustrating when things don’t work, and Scott certainly had his share of frustrations over those couple of weeks. Eventually, with my help, he got everything working. Check out the video above to see Scott “checking” that his tub works.

Next step: the hot tub interior.

More video updates from Scott’s build

Adding a hot tub to your own pool?

A project like Scott’s lives or dies on the plumbing design: which pump feeds what, how the tub heats separately, and how the overflow is switched on and off. My custom hot tub and pool combo design consultancy covers the layout and plumbing for both. If you already have the design and just need the plumbing worked out, there’s the hot tub and pool combo plumbing consultancy. For a spillover like Scott’s, see Adding a spill-over hot tub to an existing swimming pool and How to correctly size a swimming pool overflow or spillover.

If it’s a standalone hot tub you’re after, my DIY hot tub plans give you CAD drawings, the plumbing layout, a parts list and the video course.

FAQs

Can I add a hot tub to an existing pool?

Yes. Scott’s build shows one way: a separate block-built tub beside the pool, with its own jets, circulation and heating, and a waterfall overflow fed from one of the pool returns.

Can a hot tub use the pool’s pump, filter and heater?

It can share them, but a tub that heats separately needs its own circulation, or valves to isolate it. Scott’s tub has its own circulation pump, filter and spa pack, with the pool water only used for the overflow.

Why use self-priming pumps?

Because Scott’s equipment pad sits above the water line. A pump above the water level has to be able to pull water up to itself. See Using a priming circuit on a centrifugal pump above the water line for the alternative.

How do I test a DIY hot tub for leaks?

Fill it, close off the plumbing and check the level overnight, looking over every joint. It won’t show leaks that only appear under pump pressure, so check again when the pumps first run.

Are you adding a hot tub to your pool? Tell me about it 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