Can I add a Hot Tub to my Existing Swimming Pool?

One of the most popular questions I get asked when people are looking to renovate their backyard is, “Can you add a hot tub or Jacuzzi to your swimming pool?” Given the popular demand for this question, I just had to write this article for my reader! So let’s get to it. 

When it comes to adding a hot tub or Jacuzzi to your existing swimming pool, there are a number of things you need to consider. In this blog post, I’ll explore everything you need to think about before you embark on such a project.

How Big is the Hot Tub or Jacuzzi Going to Be?

The first thing we need to look at is size. How big is the hot tub or Jacuzzi going to be that you will add to your existing pool? This will dictate how many jets you will need to install. Remember, the maximum on a single pump is around 16 jets depending on the exact size of the pump, the head height, and the flow rate of each jet.

It’s also crucial to account for the available space around your pool. Is there enough room to build the hot tub into your current patio or deck design, or will that need to be extended? Factoring this in early can prevent costly adjustments later.

How deep do you expect the hot tub to be? Most of the hot tubs that I build have a water depth of 900mm or 35.5″.

How many people to you envisage the seating being for?

Do you want to arrange your jets into clusters or do you want to have them in a row around the middle of the back of the seat? Again, this is something to think about.

Also, consider if you want any additional features like hydrotherapy jets, LED lighting, or a sound system. These can dramatically improve the experience but require early planning for power and plumbing.

Do You Want the Hot Tub to Overflow Into Your Pool?

Most customers that want to add a hot tub to their swimming pool want it to be able to overflow into the pool. Looks great, doesn’t it? Waterfall flowing into your pool—just like you see in the resorts.

This is not a problem, and the plumbing to do this just requires that there be a swimming pool return line into the tub section. This will allow the swimming pool return line to fill up the hot tub and then, once full, it will overflow naturally into the pool.

Likewise, when people get into the tub, the water displacement that a person or persons cause—approximately 70 litres or 15.5 gallons per person—will also cause this to overflow. Not a problem at all as the return line from the pool will then fill the tub back up.

The problem comes if you want your hot tub and pool to have different temperatures. Think of it like this: if your cooler pool water is being returned into your hot tub that is heating up, it is going to hamper the heating of the water for sure.

It might never actually get up to temperature! We’ll look at heating in a separate section of this post.

Another consideration is the aesthetic design of the overflow. Do you want a clean spillway edge, a cascading effect, or even a hidden channel? These options not only impact your hot tub’s appearance but also influence how the water is circulated back into the pool.

What About Chemicals?

If you want to be compliant with guidance, hot tub chemical concentrations are different from swimming pool concentrations.

This is due to the usual differences in heat between a hot tub and a pool. Obviously, this is down to personal preferences here, but if you are going to be overflowing your hot tub into your pool and then refilling from your pool into your hot tub, keeping the chemicals at the different levels is not really going to be possible.

A potential solution to this is adding a chemical-free UV system to your setup. This means you don’t need to worry about chemicals in the pool and the hot tub, as the UV light will kill all bacteria.

UV is great as you cannot overdose on it. You don’t need to test the amount that is in the water—you simply select a system that can deal with the volume of water that is going through your pool and hot tub.

Another modern solution is Ozone sanitation systems. These work similarly to UV systems by killing bacteria without adding chemicals, and can be a great eco-conscious alternative. That said, combining ozone and UV offers a robust dual-disinfection system that many high-end installations are now using.

Can I Use My Existing Pool Plumbing?

The simple answer to this one is yes and no. You can use your existing filter and your existing pump to be used as a circulation pump.

You can also use—and you should use—your existing return lines to fill the hot tub and make it overflow (if that is the style you are opting for).

What you can’t do, as I explain below, is use your pump to power the jets.

You have to be mindful here not only about the heating of the pool but on all the other elements too. You are increasing the volume of the water that is going to need to not only be heated but filtered too.

If your pool has been designed in a way that it is close—if not on the limit—of the filtration and heating capabilities of the kit you have in place, you are going to want to think about changing them and making sure that the ones you buy are sized correctly for the new total volume of water.

Pro tip: Check your current system’s gallons-per-minute (GPM) flow rate and maximum volume capacity before making any upgrades. It’s better to over-engineer your system slightly than risk underperformance later.

Can I Use My Pool Pump for the Jets?

Unfortunately, not. Pool pumps are designed to move large bodies of water through a filter and return the filtered water back to the pool.

They are not designed to force water under pressure through a jet. Also, generally, a pool will have a circulation pump that will be less than 1HP.

A jet pump, as a bare minimum, will be 2HP. You also have to bear in mind that each jet has its own flow requirements. If you don’t have enough flow into the jet, then it will not function correctly.

Therefore, when you are adding a hot tub to your existing swimming pool, you need to put in a separate plumbing system for your jets.

You don’t need to filter this as the pool filter will do that for you. You should, however, have two lower drains going into a single-speed jet pump (if you are not heating the hot tub separately) and a dual-speed pump if you are, and then back out into your hot tub. It is a simple plumbing system that is needed to give you the result you are looking for.

Also consider adding an air blower to your jet system. This mixes air with the water for a more invigorating massage experience. Many luxury spas include this feature, and it’s relatively simple to integrate at the build stage.

What About Heating the Hot Tub?

Heating the hot tub separately from the pool—or to a different temperature from the pool—is where it becomes a little tricky. You can’t do this on your existing plumbing without shutting off the overflow while your hot tub heats.

You need to have a separate heating circulation system if you plan to heat your pool and your hot tub to different temperatures. Once up to temperature, you can then change the valve so that it overflows again and is refilled from the pool; but you can’t heat and overflow at the same time.

I guess you physically can if you want to, but it is going to be counterproductive and cost you more. Remember, when you are using the overflow and returning water from the pool, you will be returning cooler water, so the temperature will drop in the hot tub.

We are not talking huge amounts here, but obviously, over a period of time, it will reduce the temperature of your hot tub. Logical, I guess, if you are returning cool water to the hot tub.

If you are going to heat the hot tub separately, then you are going to need to have a dual-speed pump added to the system. The low speed will be used for circulation and heating the tub. The high speed will be used for the jets.

Many installers now integrate smart controllers that let you manage the temperature remotely via an app. This can help preheat your hot tub before use or keep it in eco mode until you’re ready. Not a necessity—but definitely a luxury worth considering.

What’s the Best Way to Heat My Hot Tub?

Adding a hot tub to an existing swimming pool can be a wonderful enhancement to your backyard oasis. When it comes to selecting the best heating method for your hot tub, each option comes with its own set of pros and cons. Let’s explore the four main heating methods: gas, propane, air source heat pump, and electric, to help you make an informed decision.

Gas Heating:

Pros: Gas heaters are known for their rapid heating capability, quickly raising the water temperature in the hot tub. They are suitable for larger hot tubs or when immediate heating is desired. Gas heaters also operate independently of ambient air temperature, making them effective even in colder climates.

Cons: The main drawback of gas heaters is their higher operating cost compared to other heating methods. Additionally, they require a separate gas line, installation, and periodic maintenance, which can add to the overall expenses.

Propane Heating:

Pros: Propane heaters share many advantages with gas heaters, offering fast heating and efficiency. They are suitable for locations where natural gas is not available, as propane can be stored in tanks on-site.

Cons: Similar to gas heaters, propane heaters come with higher operating costs and require regular refills of propane tanks, which may become inconvenient and expensive in the long run.

Air Source Heat Pump:

Pros: Air source heat pumps are energy-efficient and eco-friendly heating options. They extract heat from the surrounding air and transfer it to the hot tub water, making them cost-effective to operate. They also work well in moderate climates, where air temperatures are consistently above freezing.

Cons: Air source heat pumps might struggle to maintain desired water temperatures in colder climates or during winter months, as their efficiency decreases in low ambient temperatures. They may also take longer to heat the water compared to gas or electric heaters.

Electric Heating:

Pros: Electric heaters are easy to install and generally have lower upfront costs compared to gas or propane heaters. They can be an efficient heating option in areas with mild climates or for smaller hot tubs.

Cons: Electric heaters tend to be less energy-efficient and may result in higher operating costs, especially for larger hot tubs or during colder weather. They may also take longer to heat the water compared to gas or propane heaters.

Bonus Tip: If you have solar panels at home, pairing them with an electric heater or a heat pump can reduce your ongoing heating costs significantly while staying green.

Do I Need a Spa Pack for My Hot Tub?

The answer to this question really depends on how you plan to heat your hot tub and also how you plan to control your jets.

A spa pack not only contains a heating element (electric) but it also provides the controls for your jets, filter cycles, and purge cycles.

The latter two are less important if you are overflowing your hot tub and then using the pool filter, but you still have to think about how you are going to control your jets. Also, how are you going to control your heating?

If you want to heat your hot tub separately and you plan to do so using electric, then yes, you do.

If you plan to use another heating method like an air source heat pump or propane, then whether you use a spa pack comes down to how you plan to control your pumps.

You need to be able to switch your pump into a circulation or low-speed mode for heating. It is simple enough to wire in a switch to do so. Likewise, for your jets, you can wire in a switch for the high speed.

If it were me, I would use one in conjunction with whatever heating method I was using so I can make use of the thermostat as well as the jet controls. It makes life a lot easier in my opinion.

You can also go with a digital spa pack that includes touchscreen panels or Wi-Fi integration for full remote access. It might sound like overkill now, but having everything automated and app-controlled becomes incredibly convenient in the long run.

To Sum it Up

Yes, it is totally possible to add a hot tub or Jacuzzi to your existing pool. Before you embark on the project, you need to have a clear plan of action. You need to understand how you are going to heat it—if you indeed are—as well as how you are going to control your jets.

With thoughtful planning, the right equipment, and a clear understanding of how the systems interact, you can seamlessly integrate a hot tub into your pool setup and take your backyard experience to a whole new level.

If you’re new here, then don’t forget to check out my other blogs here or my youtube channel here. I post very frequently and a couple of months following me and you’ll be a semi DIY hot tub pro yourself!

Can I Help You?

If I can help you in any way I would love to hear from you. You can get in touch using the form below.

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