Can I Add an Air Source Heat Pump to My Hot Tub? How to Connect One Step by Step

Last updated: September 2026

Can you add an air source heat pump to your existing hot tub? Yes. Every hot tub I’ve come across can take one, whether it’s a shop-bought acrylic tub or a DIY build. But “compatible” might not mean quite what you think, and there are a few things to get right on sizing, flow, plumbing and electrics.

Many of the bigger hot tub companies have install teams who’ll come and fit one for you. Here at buildahottub.com I focus on doing it yourself, so this guide explains exactly what’s involved.

Is my hot tub compatible with a heat pump?

When people ask whether their tub is compatible, they usually mean: can I control the heat pump from my topside panel, the keypad where you switch the jets on and set the temperature? That level of compatibility is possible, but it’s harder and more expensive than you’d think.

Option 1: a brand-matched heat pump

Balboa and Gecko both make heat pumps that talk to their own spa packs. But you need the right pack, the right software and the right keypad. For example, Balboa’s Clim8zone only works with certain BP control systems labelled “C8Z”, with updated system and panel software. Just having a Balboa pack doesn’t mean it’ll work. The same goes for Gecko. In my opinion, these branded units are also expensive for the heat they put out. I looked at one in my Balboa Clim8zone first look.

Option 2: control it by flow (works with any tub)

This is how I fit them, and how most of my customers do it. Here’s how it works:

1. When the tub is below temperature, the spa pack calls for heat. It switches on the heater relay and runs the pump that pushes water through the heater.
2. That water now also flows through the heat pump.
3. The heat pump has its own flow switch. When it senses flow, it starts heating (usually after a short delay). No flow, no heat.
4. When the spa pack reaches temperature, it stops the pump, the flow stops and the heat pump stops.

So you’re controlling the heat pump indirectly, through flow. Every hot tub has a pump, so every hot tub is compatible. I go into this in more detail in How to control a heat pump with any hot tub spa pack.

Don’t plug it into the heater terminals

A common mistake is to disconnect the electric heater and wire the heat pump into its terminals. Don’t. That output is a switch, so it would cut the power to the heat pump mid-cycle instead of letting it shut down properly. Depending on the model, that can shorten the life of the parts or damage the unit. Power the heat pump from its own supply (it can come off the main terminal block, used only as a connector). The spa pack never switches it directly.

Whether you disconnect the old element is up to you. Many people leave it in place, switched off, as a boost for very cold days.

How big a heat pump do I need?

There’s no one-size-fits-all answer, so my rule of thumb is simple: go for the biggest unit that fits your budget.

• I wouldn’t bother with a 5kW unit. Some will disagree, but I don’t think the gains are worth the money.
• For a 4–6 person tub, look at 9kW as a minimum.
• For anything bigger, look at 12kW as a minimum.
• There’s no real need to go beyond about 24kW for a hot tub.

Why go big? Because a heat pump’s rated output is measured in warm conditions, and it drops as the air gets colder. For example, the Comfortline 7kW is rated at 7kW with 26°C air but 5kW with 15°C air, and the 20kW model at 20kW in warm conditions but 14kW at 15°C. A small unit that only gives 2–3kW in winter is no faster than the spa pack heater. A bigger one heats faster and holds its performance better when it’s cold. For the full sizing method, see How to choose the right air source heat pump for your hot tub or pool, and for the bigger picture, the ultimate guide to air source heat pumps for hot tubs.

Check the flow before you buy

Every heat pump has a minimum flow rate, and it won’t heat without it. The Comfortline 7kW wants 2–4m³ an hour (roughly 9–18 US gallons a minute). The 20kW wants 8–10m³ an hour (roughly 35–44 US gallons a minute). A small circulation pump may not reach the higher figure, so check your pump’s flow against the heat pump’s spec sheet before you order. If you’re not sure, see How to correctly size a hot tub pump.

Where to put it

Location matters more than people expect:

• Airflow. Leave plenty of space around it, typically at least 30cm (12in) from walls, and nothing in front of the fan. Always follow the manufacturer’s clearances.
• Never box it in. It can’t go inside a shed or a tight enclosure. It’s pulling heat out of the air, so it needs a constant supply of fresh air.
• Keep the pipe run short. Every metre loses a bit of heat and adds friction.
• Think about noise. Keep it away from bedroom windows and your neighbours’ patio. See How noisy is an air source heat pump?
• A solid, level base, raised a little so condensate can drain away.

For a checklist before you buy, read 5 considerations before you install an air source heat pump on your hot tub.

What you’ll need

• 2in pipe for the runs to and from the heat pump. Measure the distance there and back, then add 30%. Flexible pipe makes life much easier inside a tight cabinet.
• A short length of 1.5in or 50mm pipe, depending on the heat pump’s unions.
• 2in 90° elbows and straight couplers.
• Three ball valves for the bypass.
• 2in to 1.5in (or 50mm) reducers to suit the heat pump’s unions.
• PVC primer and cement.
• Pipe insulation for any pipe above ground.

If you’d rather not source it bit by bit, we sell air source connection kits on parts4tubs.co.uk, in 1.5in and 2in, in different lengths, and a version with a flapper valve for single-pump systems.

Step by step: connecting the heat pump

1. Find the pump that heats

Open the service panel and see what you’ve got. If you use more than one button to run the jets, you probably have more than one pump. Many tubs have a small circulation pump as well as one or more jet pumps. Others use a two-speed pump, where low speed does the circulation.

The easy test: turn the tub on and turn the temperature up. Only one pump (or one speed) should run. That’s the one feeding the heater, and that’s the one you’ll use to feed the heat pump.

2. Isolate and drain

Turn the power off at the isolator and make sure it can’t be switched back on. Then drain the tub.

3. Trace the plumbing and cut in after the spa pack

Follow the pipes. Water from the lower drains goes into the front of the pump. From the pump it goes through the filter, into the spa pack’s heater and then back to the jets. If you have several pumps, only one follows this route. That’s your circuit.

You want to cut into the pipe just after the spa pack heater. The spa pack is the control box that the pumps, blower and lights plug into. Here’s an example:

Remove a section of pipe about 10cm (4in) long with pipe cutters or a hand saw. Be careful not to nick any other pipes. Then glue in a pair of 2in 90° elbows to take the pipework out of the cabinet to the heat pump. You’ll probably need to cut holes in the cabinet to get the pipes out, so plan where they’ll look tidiest and won’t block the access panels.

4. Build the bypass

This is the important bit. Fit three ball valves as shown below: one on the pipe to the heat pump, one on the pipe back from it, and one on the main line between the two tees.

The bypass does two jobs:

1. Isolation. Close the two outer valves and open the middle one, and the heat pump is out of the circuit for servicing or winterising, while the tub carries on as before.
2. Flow control. If your jets feel weak, crack the middle valve open to let some water skip the heat pump.

Just remember that any water going through the bypass isn’t being heated, so the heat pump works less efficiently the more you open it.

5. Reduce down at the heat pump

Run 2in pipe to and from the heat pump, even though most units have 1.5in or 50mm unions. Keeping the long runs at 2in keeps the friction down and the flow up. At the unit, use 2in reducing bushes and a short length of 1.5in (or 50mm) pipe to make the connection. Insulate any pipe above ground. For good joints, see How to make the perfect PVC solvent weld joint.

6. Electrics

The heat pump needs its own protected supply sized to the manufacturer’s spec. For example, the Comfortline 7kW recommends an 8A breaker with a 30mA RCD, and the 20kW recommends 23.5A. Check that your existing supply can carry the tub and the heat pump together. In the UK, work on a hot tub circuit is covered by Part P and should be done or checked by a registered electrician. In the USA, follow NEC Article 680 and your local permit rules. See A guide to hot tub electrics.

7. Set the temperatures and test

Set the heat pump’s thermostat to 40°C (104°F) and set your topside to the temperature you actually want. The spa pack then decides when to heat, and the heat pump does the work. Refill, open the valves, bleed any air and check every joint for leaks before you close the cabinet.

Single-pump tubs: watch your jet flow

You’re adding pipe, bends and the heat pump’s heat exchanger to the circuit. All of that adds friction. On a tub with a separate circulation pump, that’s rarely a problem. On a tub with one pump doing both jobs, you may notice the jets are weaker.

• First, open the bypass valve a little. You’ll lose a bit of heating efficiency but get your jet flow back.
• In the worst case, close the heat pump’s two isolation valves and run on the bypass while you’re using the jets. That’s rarely needed.
• A better long-term fix is a dedicated circulation pump. See How to add a circulation pump to a hot tub and Can I add an air source heat pump to a hot tub with a dual speed pump?

Can you automate the valves?

If you’re an experienced DIYer, yes. You can use normally closed motorised or solenoid valves instead of the manual ones. The photo below shows a small 1in valve to illustrate the idea, but I wouldn’t go below 2in, or your flow will drop dramatically.

On a two-speed pump, you can power the valves from the pump’s low-speed output. On low speed they open and send water through the heat pump. On high speed they lose power, close and send the water straight to the jets. The principle is simple, but you’re working with mains voltage (230V in the UK, 240V in the USA), so only do this if you’re genuinely competent with electrics, and get it checked.

Troubleshooting

• Flow error on the heat pump. This is normal when the spa pack stops the pump. If it happens while the pump is running, check the filter, valves and the bypass setting, and compare your pump’s flow with the heat pump’s minimum.
• Heat pump runs but the tub won’t warm up. The bypass may be too far open, or it may simply be too cold outside for the unit’s size. See Help! My air source heat pump is not heating my hot tub.
• Ice on the fins in winter. That’s what the defrost cycle is for. See How to defrost a Comfortline air source heat pump.
• Weak jets. Open the bypass a little, or add a circulation pump.

Real installs

If you’d like to see this done for real, I’ve written up three:

• How I added an air source heat pump to an existing hot tub: my friend Paul’s six-week-old acrylic tub, step by step.
• Why I fitted an air source heat pump to my hot tub: my own DIY tub, where I couldn’t drill new holes.
• How I reduced the running costs of my hot tub by 66%: the before and after numbers.

Need the parts, or planning a new build?

For UK readers, we stock heat pumps and ready-made connection kits at parts4tubs.co.uk. In the USA, parts4tubs.com has the pumps, valves and fittings. If you get stuck, ask in the comments below.

If you haven’t built your tub yet, it’s far easier to plan the heat pump loop from the start. My DIY hot tub plans include the plumbing layout and parts list.

FAQs

Will an air source heat pump work with any hot tub?

Yes, if you control it by flow. The heat pump heats whenever the tub’s pump pushes water through it. A brand-matched unit that shows on your keypad needs a specific spa pack, software and topside.

What size heat pump do I need for a hot tub?

I’d say 9kW as a minimum for a 4–6 person tub and 12kW or more for bigger tubs. There’s little point going beyond about 24kW. Remember that output drops in cold weather.

Can I plug the heat pump into the spa pack’s heater connection?

No. The heater output is switched, so it would cut power to the heat pump mid-cycle. Give the heat pump its own protected supply.

Will adding a heat pump void my hot tub warranty?

Very possibly. Cutting into the plumbing or changing the electrics on a new shop-bought tub will usually void the manufacturer’s warranty, so check first.

Do I need to keep the electric heater?

No, but I would. Leave it connected, switched off or set lower, as a backup or a boost in very cold weather.

Any questions about adding a heat pump to your tub? Drop them 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