CASE STUDY – How to Add a Hot Tub to an Existing Pool

Last updated: September 2026

Today, we’re diving into an exciting project from Michigan, where Joe, a seasoned builder, decided to add a hot tub to his existing swimming pool. Let’s walk through this build and see how it all came together.

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Project Overview

Joe reached out to me a buildahottub.com a few months ago with a clear vision: he wanted to add a hot tub to the upper right-hand corner of his beautiful backyard pool. 

The first step, as with any project, was careful planning. Joe and the I exchanged ideas back and forth until we landed on a design that worked. 

Originally, they considered adding a tanning ledge, but during construction, Joe decided it would be more practical to replace it with a step — a great reminder that designs often evolve once the build is underway.

Adjustments to the Pool Setup

One of the first challenges Joe faced was relocating the pool’s skimmer. The existing skimmer was positioned where the new hot tub would go, so it had to be moved a few feet to the left. It was important not to simply cap it off, as doing so would have disrupted the pool’s original water circulation and filtration system. Instead, moving the skimmer preserved the pool’s functionality while making space for the new addition.

Building the Hot Tub Walls

Instead of altering the pool’s existing retaining walls, Joe chose to build two new walls for the hot tub. As a professional builder, Joe was comfortable with poured concrete construction — the same method used for his original pool. He drilled into the existing structure to tie in new rebar, ensuring the new walls would be structurally sound.

Joe then formed and poured the new concrete walls, carefully bracing the molds to prevent them from buckling under the weight of the concrete. Good bracing is essential to avoid uneven or bowed walls — something any DIY builder must keep in mind.

Plumbing the New Hot Tub

When it came to plumbing, Joe went with a proven and smart approach: keep the pool and hot tub systems separate. Instead of sharing equipment, the hot tub would have its own dedicated system — including its own filter, spa pack, heater, and a dual-speed pump. This setup allows Joe to heat the hot tub to a different temperature than the pool, which would have been much more complicated if the systems were combined.

Since Joe lives in Michigan, where winter temperatures regularly drop below freezing, he had to install the hot tub plumbing below the frost line — about a couple of feet deep — to prevent pipes from freezing during winter.

Importance of Control Room Placement

Another critical factor was the placement of the control room. I emphasized that hot tub pumps are centrifugal pumps — they can’t suck air to prime themselves. Instead, they rely on gravity to feed water to the pump. That’s why the control room needed to be positioned below the water level, ensuring proper water flow and reliable system operation.

Finishing Touches

Once the concrete forms were removed, Joe and his team moved on to the finishing work: waterproofing, sealing, painting, and installing tile around the waterline. Attention to these details ensured that the new hot tub would not only function well but also match the aesthetic of the existing pool.

The Final Result

The final outcome was absolutely stunning. The hot tub blends so seamlessly with the pool that it looks like it was part of the original design. Joe also installed a protective dome over the pool and hot tub, allowing him to enjoy his backyard oasis even during the cold Michigan winters.

Joe summed up the experience and his warm words at the end of the project really makes this build worthwhile!

Conclusion

Joe’s project is a perfect example of how you can successfully add a hot tub to an existing swimming pool with the right planning, expertise, and attention to detail. By carefully designing the layout, moving critical plumbing elements, building strong new walls, and setting up an independent plumbing system, Joe not only preserved the integrity of his pool but also added a beautiful new feature that looks like it was always meant to be there. With a bit of hard work and the right guidance, you too can transform your backyard into a luxurious, year-round retreat.

Planning your own build?

If a build like this has you thinking, my DIY hot tub plans give you the CAD drawings, plumbing layout, parts list and video course. If your space needs something custom, I can draw it up with architectural CAD and a 3D plumbing design.

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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