Onda Mini Heat Pump Review: Is a Plug-In Hot Tub Heat Pump Worth It?

Last updated: September 2026

I talk a lot about air source heat pumps on this blog and on my YouTube channel. Most of them need an electrician, a hard-wired supply and a decent budget. The Onda Mini is different. It’s a small plug-in heat pump that promises to cut your hot tub running costs without the big upfront bill.

So does it deliver, who is it for, and is it still the bargain it was? Let’s take a look.

What is the Onda Mini heat pump?

The Onda Mini is a range of compact “plug and play” air source heat pumps for hot tubs and small above-ground pools. It comes with a normal plug, so the electrical side is far simpler than a hard-wired heat pump. With a maximum of 7kW on the largest model, it won’t heat a swimming pool, but it’s a good match for a hot tub.

Spec	3.5kW	5kW	7kW
Heat output (26°C air)	3.5kW	5.8kW	7kW
Electrical input	0.54kW	0.84kW	1.02kW
Current (running / max)	2.35A	3.65A / 6.5A	4.43A / 7.5A
Water flow	1–2m³/h	2–3m³/h	3–4m³/h
Max water volume	<20m³	<28m³	<35m³
Noise at 1m	56dB(A)	57dB(A)	59dB(A)
Weight	24kg	34kg	38kg
Typical UK price (Sept 2026)	~£927	~£899–£1,220	~£1,371

All sizes use R32 refrigerant and a titanium heat exchanger, run on 220–240V single phase, have 32mm inlet and 38mm outlet connections, and are rated to run in air from 10°C to 43°C. Specs and prices are from JustSpaParts (3.5kW), JustSpaParts (5kW), JustSpaParts (7kW) and Hot Tub Movers. Prices vary between retailers.

How is a mini heat pump different from a regular one?

There are three main differences: heating capacity, efficiency in the cold, and the electrical hook-up.

• Capacity. The Onda range tops out at 7kW, which is where many “regular” heat pumps start. On a hot tub that’s fine. It’ll hold temperature and heat up faster than a 2–3kW spa heater in mild weather.
• Efficiency and cold weather. The Onda Mini is an on/off unit, so it runs at full power and then stops. Its COP is about 6.5 in warm air and about 4.5 at 15°C. An inverter like the Comfortline throttles back when it’s holding temperature, gets a higher COP doing so, and is rated down to 0°C rather than 10°C.
• Electrics. The Onda plugs into a socket. A regular heat pump is hard-wired, like your hot tub.

I’ve gone deeper on this comparison in what is the difference between the Onda and the Comfortline?

Can I use an Onda Mini all year round?

Not in the UK or most of Europe. Its rated operating range starts at 10°C (50°F), so once the air drops below that, it’ll struggle to heat at any meaningful COP. You’ll need the tub’s electric heater to take over.

That said, if you mostly use your tub from spring to autumn, or you don’t mind switching back to electric in a cold snap, it can still save you a lot of money. If you’re paying for 1kW of electricity and getting 4.5kW or more of heat back in mild weather, that’s quite a saving.

If you want to heat through the winter, you need a unit rated for it. Look at the Comfortline (rated to 0°C, and mine has kept going at -4°C) or the Vian Power Plus models (rated to -10°C).

The positives

• It plugs in. There’s no hard-wiring, so the electrical side is simple. It still needs to be plugged into an outdoor-rated, RCD-protected socket (not an extension reel), and some retailers recommend professional installation.
• It’s small. The small footprint means it’s less intrusive in a smaller garden or backyard.
• You can store it for the winter. Drain it and take it indoors when it’s too cold to be useful.
• It’s efficient in mild weather. It gives a real saving over a resistance heater from spring to autumn.

The negatives

• It isn’t an all-season heat pump. Below 10°C air, the electric heater is doing the work.
• It’s on/off, not an inverter. That means a lower average COP and more noise than an inverter of the same size.
• The price advantage has gone. It used to come in under £800. Now UK retailers list it at roughly £900–£1,370, which is the same money as, or more than, a 7kW inverter Comfortline with WiFi at £897. The Comfortline does need an electrician, though, so factor that in.

How do I connect an Onda Mini to my existing hot tub?

First, find a suitable place to cut into the hot tub’s pipework. Ideally, you want the heat pump just before or just after the circulation pump.

Here’s the ideal place to cut the pipes on this particular hot tub.

Next, use an air source heat pump connection kit. It has everything you need to connect a heat pump to an existing tub, and it’s done in a way that lets you take the heat pump off for winter storage, which is pretty handy on a warm-season unit like this.

Watch the direction of flow. The front of the pump is always the suction side. In the diagram below, the water goes into the heat pump on the blue arrow and out on the red arrow, which matches the water being drawn into the front of the pump.

Only fit this model if you have a separate circulation pump. The Onda Mini wants 1–4m³/h of flow depending on size, and its small connections won’t take the full force of a jet pump. You might get away with a jet pump by opening a bypass slightly, but I wouldn’t advise it, so it’s on your own head if you decide to do it. If your tub doesn’t have a circulation pump, see how to add a circulation pump to a hot tub or, for two-speed pumps, can I add an air source heat pump to a hot tub with a dual speed pump?

You’ll also want to decide how the heat pump and the spa pack share the heating. How to control a heat pump with any hot tub spa pack explains the options. There’s a full step-by-step in can I add an air source heat pump to my hot tub?

Common mistakes with plug-in heat pumps

• Expecting winter performance. It’s rated from 10°C air. Plan on the electric heater for the cold months.
• Running it off an extension lead. Use a proper outdoor, RCD-protected socket. See a guide to hot tub electrics.
• Too much flow, or none. A jet pump will overwhelm it, and it needs water flowing through it to heat at all. Check the flow window for your size.
• Leaving water in it over winter. If you store it, drain it fully first. Frost damage inside a heat exchanger isn’t a cheap fix.
• Skipping the cover and insulation. A 3.5kW unit can’t keep up with a tub that’s losing heat fast. See the ultimate guide to hot tub covers.

My verdict

The Onda Mini does what it says. It’s easy to install and small, it cuts your running costs in the warmer months, and it’s simple to use. If you’re on a budget, only use your tub in the warmer months, or don’t mind the electric heater taking over in winter, it’s a good way to save money.

But the maths has changed since it launched. Now that it costs about the same as a 7kW inverter heat pump that works down to 0°C, I’d only choose the Onda if plug-in really matters to you (a rental, a tub you might move, or no easy way to run a new cable). If you want something for the whole year, go for the Comfortline range instead.

Where to buy

The Onda Mini is still sold by UK spa retailers, but parts4tubs.co.uk no longer stocks it. The plug-in alternatives on parts4tubs.co.uk are the HeatSeeker AG Mini (2.9kW, plug and play with an inline RCD, £453.88 at the time of writing), and the Gecko in.temp Mini 3kW, which talks to Gecko in.ye, in.yt and in.yj spa packs and is rated down to 0°C. For year-round heating, the Comfortline Inverter range starts at the 7kW with WiFi.

Not sure what size you need? Read how to choose the right air source heat pump for your hot tub or pool, and for the full picture, the ultimate guide to air source heat pumps for hot tubs.

FAQs

Can the Onda Mini just plug into a normal socket?

Yes. It comes with a plug and draws at most about 6.5–7.5A on the bigger models. It should be on an outdoor-rated, RCD-protected socket, not an extension reel, and some retailers recommend a professional install.

Does the Onda Mini work in winter?

Not really. It’s rated to run in air from 10°C (50°F) upwards. Below that, expect to rely on your hot tub’s electric heater.

What size Onda Mini do I need for a hot tub?

For most hot tubs, the 5kW or 7kW. The 3.5kW suits small or inflatable tubs. Check that your circulation pump gives the flow the model needs (1–2m³/h for the 3.5kW, up to 3–4m³/h for the 7kW).

Is the Onda Mini an inverter heat pump?

No. It’s an on/off unit that runs at full power until the water is up to temperature, then stops.

Can I connect an Onda Mini to my jet pump?

I wouldn’t. It’s designed for the gentler flow of a circulation pump. A jet pump pushes far more water than it wants.

Got a question about adding a heat pump to your tub? Drop it 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