Can You Add a Hot Tub to an Existing Swimming Pool?

Last updated: September 2026

“Can you add a hot tub or Jacuzzi to your swimming pool?” is one of the most common questions I get from people renovating their backyard. The answer is yes, and it’s a popular upgrade. But there are a number of things to think about before you start, from size and overflow to chemicals, plumbing, heating and controls.

If you’d rather see it built than read the theory, take a look at the case study of a hot tub added to an existing pool (Joe from Michigan) and Scott’s build in Arizona.

How big will the hot tub be?

Size dictates how many jets you’ll fit. A single pump maxes out at around 16 jets, depending on the pump, the head height and each jet’s flow rate. Also think about the space around the pool: can the hot tub fit within the current patio or deck, or will that need extending? Factor that in early to avoid costly changes.

How deep? Most hot tubs I build have a water depth of 900mm (about 35in).

How many people, and what seating and jets?

Decide how many people you want to seat, and whether you want jets in clusters or in a row across the back of each seat. Think about extras too, such as hydrotherapy jets, LED lighting or a sound system. They improve the experience but need early planning for power and plumbing. Read DIY hot tub jets and hot tub lights for more.

Do you want the hot tub to overflow into the pool?

Most people who add a hot tub to a pool want it to overflow into the pool, like a resort. That’s not a problem. The plumbing just needs a swimming pool return line feeding the tub. The return fills the hot tub, and once it’s full, it overflows naturally into the pool. When people get in, the water they displace (about 70 litres or 15.5 US gallons per person) also overflows, and the pool return refills the tub. For the sizing side of overflow, see how to size a pool overflow or spillover and adding a spill-over hot tub.

The catch comes if you want the hot tub and pool at different temperatures. Cooler pool water returning into a tub that’s heating up hampers the heating, and it might never reach temperature. There’s more on heating below.

Also think about the look of the overflow: a clean spillway edge, a cascade or a hidden channel. Each affects the appearance and how the water circulates back into the pool.

What about chemicals?

Hot tub chemical levels differ from swimming pool levels, mostly because of the temperature difference. If you overflow the tub into the pool and refill the tub from the pool, keeping two different sets of levels isn’t really possible. See the guide to balancing hot tub chemicals for the hot tub ranges.

One option is to add a UV system or ozone alongside a lower level of sanitiser. UV can’t be overdosed, and you don’t need to test how much is in the water: you choose a system rated for the volume of water passing through. Ozone works in a similar way, and some high-end installs combine the two. But neither leaves a residual sanitiser in the water, so you’ll usually still want a low level of chlorine or bromine as a back-up, especially in a hot tub where bathers load the water quickly. Read ozone in a hot tub.

Can I use my existing pool plumbing?

Yes and no. You can use the existing filter and pump as circulation for the tub. You can, and should, use the existing return lines to fill the tub and make it overflow, if that’s your style. What you can’t do is use the pool pump to power the jets.

Bear in mind that you’re increasing the volume of water to heat and filter. If your pool is already close to the limit of its filter and heater, you’ll want to upgrade them and size them for the new total volume.

Pro tip: check your current system’s flow rate (GPM) and maximum volume capacity before making upgrades. It’s better to over-engineer slightly than risk underperformance. For sizing, see heater size for your pool or hot tub and pool pump upgrade tips.

Can I use my pool pump for the jets?

No. Pool pumps move large volumes of water through a filter and back to the pool. They aren’t designed to force water under pressure through jets. A pool circulation pump is also usually below 1HP, whereas a jet pump is 2HP as an absolute minimum, and each jet has its own flow requirement. So you need a separate plumbing system for the jets.

You don’t need to filter that jet loop, because the pool filter does it. You should have two lower drains going into a single-speed jet pump (if you aren’t heating the tub separately) or a dual-speed pump (if you are), then back out to the tub. Use drain covers that meet the VGB standard where applicable. Read how hot tub plumbing works and why pool and hot tub plumbing should remain separate. Consider adding an air blower for a more invigorating massage: the guide to hot tub air blowers.

Heating the hot tub

Heating the tub separately, or to a different temperature from the pool, is where it gets tricky. You can’t do it on the existing plumbing without shutting off the overflow while the tub heats. You need a separate heating circulation if you want two temperatures. Once it’s up to temperature, you can switch the valve so it overflows and refills from the pool again, but you can’t heat and overflow at the same time. You physically can, but it’s counterproductive and costs more, because you’re returning cooler pool water into the tub.

If you heat the tub separately, you’ll need a dual-speed pump: low speed for circulation and heating, high speed for the jets. See variable speed pump in a hot tub.

Which heating method?

Method	Pros	Cons
Gas	Fast heating, works in any weather, good for bigger tubs	Higher running cost, needs a gas line and servicing
Propane	Fast, useful where there’s no mains gas	Higher running cost, tank refills
Air source heat pump	Efficient and cost-effective to run	Slower, and efficiency falls in very cold air
Electric	Low upfront cost, easy to install	Highest running cost for larger tubs or in the cold

Solar panels can offset the cost of either an electric heater or a heat pump. I go into detail in the best method to heat a DIY hot tub, the ultimate guide to air source heat pumps and how to choose the right air source heat pump, and gas heat for hot tubs.

Do I need a spa pack?

It depends on how you’ll heat and how you’ll control the jets. A spa pack contains an electric heating element and controls the jets, filter cycles and purge cycles. The filter and purge cycles matter less if you’re overflowing and using the pool filter, but you still need to control the jets and the heat.

If you’ll heat separately with electric, then yes. With an air source heat pump or propane, it comes down to how you’ll control the pumps. You need to switch the pump into circulation or low speed for heating and to high speed for the jets, which a simple wired switch can do. Personally I’d use a spa pack with any heating method, so I get the thermostat and jet controls together. You can also choose a digital spa pack with a touchscreen or Wi-Fi for remote control. See how to select a replacement spa pack and Control My Spa from Balboa.

Safety and electrics

A hot tub beside a pool needs proper electrical bonding, RCD or GFCI protection and the right clearances, and the electrics should be done by a qualified electrician. See ground bonding a hot tub and hot tub wiring explained. Check local rules and any permit requirements too: permit for my hot tub.

To sum up

Yes, it’s completely possible to add a hot tub to an existing pool. Have a clear plan for how you’ll heat it, how you’ll control the jets, and how the water will move between the two. With the right equipment and a good understanding of how the systems interact, you can build it in seamlessly. There are more combined designs in hot tub and pool combo and hot tub pool combo 2.

Want help designing yours?

Two of my services are aimed at exactly this. The hot tub and pool combo plumbing consultancy is for DIYers whose structures are built and who need the plumbing designed for both features: it includes 3D plumbing schematics, a parts specification and ongoing email support (it doesn’t cover structural design or CAD). If you want both designed together, the custom hot tub and pool combo design consultancy includes a 3D model, plumbing layout, architectural CAD drawings, a build guide and a parts quotation.

FAQs

Can you add a hot tub to an existing swimming pool?

Yes. It’s a common upgrade. You can even overflow the hot tub into the pool using the pool’s return line, but the jets need their own pump.

Can I use my pool pump for hot tub jets?

No. Pool pumps aren’t built to push water under pressure through jets. You need a separate jet pump of at least 2HP with its own drains.

Can the hot tub be hotter than the pool?

Yes, but you need a separate heating circulation and have to shut off the overflow while it heats. Cooler pool water returning into the tub would otherwise stop it reaching temperature.

What about chemicals if the water is shared?

You can’t keep two sets of levels if the water moves between them. UV or ozone with a low sanitiser level is a good approach, but neither replaces a residual sanitiser.

Do I need a spa pack?

If you heat with electric, yes. For other heating methods you can control pumps with switches, but I’d still use a spa pack for the thermostat and jet controls.

Got a question about your own build? Drop 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