Danny’s DIY Pool and Spillover Hot Tub Combo (USA Case Study)

Last updated: September 2026

Danny first got in touch with me in May 2021. He wanted to build a pool and a hot tub, with the hot tub overflowing into the pool.

Regular readers of the blog, and anyone who watches my videos on YouTube, will know I usually like to keep the waters separate in pools and spas. But Danny was very clear on what he wanted, and it’s a great example of how to do a spillover hot tub properly.

The brief

Danny wanted the water to circulate through the spa and create a waterfall overflow into his pool. He planned to use the pool’s heating and filtration system to do this, but wanted me to design a system that gave him separate control of the hot tub jets.

First things first, he needed a plan. This was a custom project (you can read more about how those work in Custom designed hot tub: the process explained), but with the right plan in place, Danny was heading in the right direction from the start.

If you’re weighing up an overflow like Danny’s against keeping the waters separate, I’ve covered the pros and cons in Hot tub pool combo: DIY design considerations and Why pool and hot tub plumbing should remain separate. The short version: an overflow works best when you’re happy for the tub to run at, or close to, the pool’s temperature, or you want the tub’s heat to help warm the pool. It’s harder if you want a properly hot tub next to a cool pool.

Enter the pool builder

There are two parts to this build: the pool and the hot tub. What I’ve found over the years is that pool builders don’t like doing hot tubs. Or, if they do, they often do them wrong.

In Danny’s case, the pool builder only worked with steel-wall pools and vinyl liners, so he wanted to do the same for the hot tub. That was never going to work. You can’t get the jets you need for a liner, and liners are a total pain on a hot tub. They’re fine for a pool, just not a tub. There’s more on this in Can I use a liner on my DIY hot tub?

Here’s part of an email Danny sent me:

“When I suggested to my pool builder that he build something like you did he was like ‘no way. I don’t do that. I only do steel walls with vinyl liners OR drop the fiberglass ones in the hole and connect the suction line, return line and blower line.’ So I showed him a picture of a steel wall hot tub and asked him ‘So can you do this?’ ‘Of course’ he said. So then I said ‘Well if I hire a mason or you hire a mason to build the concrete shell it is exactly the same thing.’ If the pool builder or the owner isn’t handy they also have to do the tile finish or find someone. But you get the idea. Now he’s like ‘OK let’s do it.’ I think once a couple of pool builders start doing it word will spread to owners or other pool builders.”

As you can see, Danny was clear on what he wanted. He just needed to find the right people to do it. If you’re working with trades on your own build, my tips in How to avoid mistakes when using contractors to build your hot tub will help.

Let’s get digging

As with any pool or hot tub build, the first job is clearing the area. Here’s the first photo Danny sent of the site. Quite the project, as you can see.

It always surprises me just how much correspondence I have with my customers. Going back through my records to find the photos and videos Danny sent for this article, there were dozens and dozens of emails spanning more than 12 months.

Start with the pool

Danny and his contractors started with the pool: a steel-framed in-ground pool with a liner. It’s quite straightforward to do, but I do recommend getting someone in for the liner.

Pool liners can be notoriously difficult to fit, so it really should be done by a pool professional, or at least someone with experience of them. I wouldn’t suggest doing a liner pool as a complete DIY project without help.

And now the hot tub

With the pool in, it was time for Danny and the team to start on the block-built hot tub. He built it from hollow CMU blocks with rebar inside, which is a popular method for DIYers (see Cinder block hot tub: a DIYer’s guide and my rebar guide).

The first job was a concrete base. With that in place, it was time to start laying blocks.

It didn’t take the bricklayers long to put the outer and inner structure together for Danny.

Next, Danny cored the holes for the gunite jet bodies. It’s a straightforward process, but it takes time. My advice is to hire a core drill. It’s much easier and quicker than doing it with a regular hand drill, like I did. I’ve covered the whole job in How to install gunite jet bodies in a DIY hot tub.

Danny then fitted the 2.5in pipes through the walls and sealed around them. He also added a sealer to the walls for extra waterproofing.

External pipework

With the gunite bodies in place, it was time for the external pipework. Something Danny did that I think works well was fitting a sheet of insulation before the plumbing went on. Then came the 1.5in air lines and 2in water lines around the tub, feeding the 9 jets. For more on insulating an in-ground tub, see DIY hot tub insulation, and for the pipe sizing, my DIY hot tub plumbing guide.

With the plumbing in, Danny filled the seat void with a mix of concrete and block. After rendering the inside, he sealed all the concrete with TEC HydraFlex, a liquid waterproofing membrane that TEC lists for pools and water features. Again, this adds another layer of waterproofing to the structure. It’s certainly starting to take shape, as you can see below. My waterproofing, grout and tile adhesive guide covers the other membranes I’d consider.

At this point, Danny needed to do some work on the outside of the structure, and as you can see, he used a waterproofer on the outside too.

The next stage was to backfill around the pool and get ready for the concrete pour.

Bring on the tiles

How good do these look? Danny went for a circular mosaic tile, and it looks absolutely fantastic. Mosaics are my go-to for hot tubs because they follow the curves of seats and steps so well. There’s more in Hot tub tiles: everything you need to know.

Danny also built a second skin of blockwork to cover the pipes, and put coping on top of the hot tub. It was really starting to take shape. I think it was around this point that his email to me said something along the lines of “this is taking ages!”

Well worth the wait, Danny.

With the tiles done, it was time to hook up the plumbing and test the overflow into the pool.

If you’re planning a spillover, how wide and deep to make it matters more than people think. See How to correctly size a swimming pool overflow or spillover and Adding a spill-over hot tub to an existing swimming pool.

The finished pool and spa

Fast forward quite a few weeks. The area around the pool has been finished, the outside of the hot tub has been clad, and this is one fantastic-looking project. Really well done, Danny. This is beautiful work, and thanks for the kind words too:

“Thought I would celebrate with you that I got the final connection hooked up today. Wanted to also say thanks as I wouldn’t have been able to do this without you. It took extra long because of pool contractor delays with the regular pool and a number of other bumps in the road.”

Planning your own pool and hot tub combo?

A combo is where the plumbing design really earns its keep: which pump feeds what, how the heat gets to the spa, and how you switch between modes. For a project like Danny’s, 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, there’s the hot tub and pool combo plumbing consultancy.

If you’d rather keep it smaller, a plunge pool next to a hot tub is a great alternative. See my DIY plunge pool guide. And if it’s just the hot tub, my DIY hot tub plans give you CAD drawings, the plumbing layout, a parts list and the video course. There are also infinity hot tub plans if you like the overflow look.

FAQs

After Danny’s build, I was asked a number of questions, so here are short answers to the common ones.

How much does a pool and hot tub combo cost?

It varies hugely with size, materials, finishes, location and how much you do yourself. As a rough guide, at the time of Danny’s build I estimated a pool builder would charge $80K+ for a setup like his, while doing it yourself could bring it under $30K. Treat those as ballpark figures from that time, and get local quotes.

How does a pool and hot tub combo work?

There are two main approaches. In a spillover combo like Danny’s, the spa shares the pool’s water: water is pumped into the spa and overflows back into the pool, so there’s one water chemistry and usually shared filtration and heating, with a separate jet pump for the spa. In a separate combo, like Jody’s build in Northern Ireland, each has its own water, filtration and chemistry, though valves can still let one heater serve both. Separate waters let you run the tub much hotter than the pool.

Can I heat the hot tub without heating the pool?

With separate waters, yes, easily. With a spillover spa, it’s harder, because the pool water flowing in keeps cooling the spa. The usual answer is valves (manual or automated) that switch the heater to “spa only” mode, recirculating the spa’s own water through the heater while the spillover is off. That has to be designed into the plumbing from the start.

Which sanitiser should I use in a combo?

With shared water, it’s one system, so you’ll usually use chlorine (often from a salt chlorinator) across both. With separate waters, you treat each on its own, and the hot tub runs at higher sanitiser levels. My hot tub chemical levels guide has the ranges, and Should I use bromine or chlorine? compares the two.

Would you go spillover or keep the waters separate? Let me know in the comments below. I read them all.

Cheers,
Andi

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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