Vian Power Heat Pump Review: C5, C5 Plus, S7 Plus and S9 Plus Compared

Last updated: September 2026

Vian is a name most hot tub owners know from chemicals, and they also make the Vian Power spa pack. The Vian Power air source heat pumps are aimed squarely at the UK and European retrofit market: people with an existing hot tub or swim spa who want to cut their running costs.

In this review I’ll go through the range, the difference between the standard and “Plus” models, the published efficiency figures (which are unusually honest), a real-world test, how to fit one, and who I think it suits.

What is the Vian Power heat pump range?

It’s a range of air source heat pumps for hot tubs and swim spas, available in the UK and Europe. There are 5kW, 7kW and 9kW sizes, in “standard” or “Plus” versions. Unlike the “mini” plug-in heat pumps (see my Onda Mini review), these are closer to the Comfortline range I have on my own tub.

All of them have a titanium heat exchanger, R32 refrigerant, a rotary compressor, a 5m power cable and a heating range of 15–40°C. The Plus models add an electronic expansion valve, WiFi, a cooling mode, and, according to the spec sheet, a pump power output (1.59A max) and an input for external control.

Model	Type	Output (27°C air)	Rated air range	Flow needed	Max water
C5 (HP-VP500)	On/off	5kW	-5°C to 40°C	2.5m³/h (41.6 L/min)	15m³
C5 Plus (HP-VP501)	Full DC inverter	2.1–5.1kW	-10°C to 43°C	2.5m³/h (41.6 L/min)	20m³
S7 Plus (HP-VP700)	Full DC inverter	1.5–7.2kW	-10°C to 43°C	3.1m³/h (51.6 L/min)	30m³
S9 Plus (HP-VP900)	Full DC inverter	1.8–9.5kW	-10°C to 43°C	4.1m³/h (68.3 L/min)	40m³

Model	Max power draw	Noise at 1m	Size (L × D × H)	Weight
C5	0.81kW	48dB	505 × 360 × 545mm	27kg
C5 Plus	0.17–0.90kW	32–45dB	470 × 290 × 430mm	23.5kg
S7 Plus	0.09–1.09kW	32–45dB	910 × 355 × 620mm	35kg
S9 Plus	0.11–1.44kW	33–47dB	910 × 355 × 620mm	37kg

All run on 220–240V single phase. The specs are from Vian’s published tables, cross-checked against the S7 Plus, C5 Plus and C5 listings on parts4tubs.co.uk and the S9 Plus listing at UK Hot Tubs.

Standard vs Plus: what’s the difference?

There are two main differences.

1. Temperature rating. The Plus models are rated down to -10°C. The standard C5 is rated to -5°C.
2. On/off vs inverter. The standard C5 is an on/off unit. When it’s on, it runs at 100%, whatever the temperature setting or the weather, and then switches off. The Plus models are full DC inverters. They work out that they might only need to run at, say, 67% to hold the set temperature in today’s conditions, and they throttle back to do it.

In short, inverter models are more efficient and quieter than on/off models, especially once the tub is up to temperature and the heat pump is just ticking over. For the small price difference, I’d pick a Plus model every time.

How efficient are they? The honest COP figures

What I really like is that Vian states the COP all the way down to -10°C. That isn’t common, and it’s very welcome, because it shows you what performance to expect in a real winter rather than on a Mediterranean summer’s afternoon.

Here are the published figures at full (100%) and half (50%) output:

Air temp	C5 (on/off)	C5 Plus	S7 Plus	S9 Plus
+25°C	6.16	5.94–8.73	6.14–10.96	6.22–11.1
+15°C	4.72	4.89–7.19	4.90–6.86	5.20–7.28
+5°C	3.53	4.28–6.29	4.00–5.03	4.11–5.17
0°C	2.94	4.08–6.00	3.65–4.48	3.76–4.61
-5°C	2.31	3.46–5.09	3.08–3.95	3.13–4.01
-10°C	Not rated	2.96–4.35	2.48–3.59	2.50–3.62

The first figure is at 100% output and the second at 50%. The C5 only runs at 100%.

Take the middle-of-the-road S7 Plus. At 25°C it’s almost 11 when it’s ticking over at half power (about 6 flat out), around 4.5 at 0°C, and still 2.5–3.6 at -10°C. So even on a bitter night you’re getting two and a half to three and a half times as much heat as you pay for in electricity. Your spa’s electric heater only ever gives you one.

The catch is output. As the air gets colder, the heat pump delivers fewer kW, so heat-ups take longer. The S7 Plus goes from about 7kW at 25°C to about 3kW at -10°C at full power.

If you want to understand what these numbers mean for your own tub, how to choose the right air source heat pump for your hot tub or pool walks through it.

Real-world testing

When the range first came out, I called Vian for more information and the inside scoop. I was told they’d had over 100 units in the field for more than a year of testing before launch, that the feedback from the testers was really positive, and that they already had a number of pre-orders. That was encouraging.

Vian also published its own winter test of an S7 Plus on a hot tub. Here’s what they reported:

• Setup: an outdoor hot tub of about 1,550 litres in Chichester, West Sussex, not under a gazebo, set to 40°C. The electric heater was disconnected, and the heat pump was in boost mode about 1m from the tub.
• Deliberately imperfect: an older, slightly waterlogged cover and uninsulated pipes.
• Economy periods: the tub didn’t heat from 10pm to 10am or from 1pm to 4pm.
• Period: 31 days from 8 December 2022 to 7 January 2023, including a very cold spell.
• Results: 116.21kWh in total, an average of 3.75kWh a day. On 10 December, at -3.1°C, it used 5.62kWh. On 4 January, at 11.5°C, it used just 1.66kWh.

At the September 2026 price cap rate of about 26p per kWh, that works out at about £1.47 for the -3.1°C day, about 43p for the mild day, and around £30 for the whole month. Remember, this is the manufacturer’s test on one tub, not independently checked, and your figures will depend on your tub, cover, weather and usage. For my own results, see my -4°C test and how I cut my running costs by 66%.

On/off, inverter and full DC inverter explained

• On/off: it draws a constant amount of power when it’s running, so it’s effectively always at maximum, and then it stops.
• Stepped inverter: it has several power levels (say, low, medium and full) and picks between them. It’s quieter and more efficient than on/off.
• Full DC inverter: it varies its power smoothly across its whole range, rather than in steps. That’s the most efficient type over a season, and the quietest. All the Vian Plus models are full DC inverters.

How do I connect a Vian Power heat pump to my hot tub?

First, find a suitable place to cut into the hot tub’s pipework. Ideally you want it just before or just after the circulation pump, with the flow the model needs (2.5–4.1m³/h). Watch the direction of flow: the front of the pump is always the suction side.

Then use an air source connection kit. It has everything you need to connect to an existing tub, with a bypass so you can isolate the heat pump. Insulate the pipe runs, too. If your tub only has a two-speed jet pump, read can I add an air source heat pump to a hot tub with a dual speed pump? or how to add a circulation pump. For a full walkthrough, see can I add an air source heat pump to my hot tub?

Location

Allow at least 500mm of clear space on the air inlet side, and ideally 1m of unobstructed space in front of the fan outlet. Stand it on a level slab or paving on its rubber feet, and think about neighbours and bedroom windows. See how noisy is an air source heat pump?

Electrics

These units are hard-wired rather than plugged in, but they draw very little (about 1.1kW max for the S7 Plus). Vian’s installation notes say the heat pump can take its power from the hot tub or swim spa supply, and many retrofits do exactly that, often with the spa heater disconnected. I used to make light of this, but I wouldn’t now: it’s still electrical work on a wet-area circuit. Get a qualified electrician to confirm the pack’s supply and terminals can take it and to certify the work. See a guide to hot tub electrics.

Control

Decide whether the heat pump or the spa pack sets the temperature, and make sure the heat pump only runs when water is flowing. The Plus models’ pump output and external control input can help here. I’ve covered the options in how to control a heat pump with any hot tub spa pack.

What’s the warranty?

• Heat exchanger: 5 years
• Compressor: 5 years
• All other parts: 2 years

If you decommission the unit over winter, make sure there’s no water left in it at all. Blow it out. Frost damage isn’t covered under the warranty.

Is it still available?

Yes, but check stock. At the time of writing, parts4tubs.co.uk lists the S7 Plus at £1,107.62 on backorder, and the C5 Plus (£882.96) and C5 (£736.74) as out of stock. The S9 Plus is still listed by other Vian dealers. It’s a UK and Europe range only.

My verdict

The Vian Power Plus range is a proper all-season heat pump for UK and European hot tubs. The published COPs down to -10°C are honest and impressive, the full DC inverter is efficient and quiet, and the 5-year compressor warranty beats the 2 years you get on many rivals, including the Comfortline. The C5 on/off model is the budget choice, but I’d spend the extra on a Plus.

For most hot tubs, I’d go for the S7 Plus. The C5 Plus suits smaller tubs, and the S9 Plus suits big tubs and swim spas. If you want more output for faster heat-ups and you’re happy with a 0°C rating, the Comfortline is the other one I’d look at. The ultimate guide to air source heat pumps for hot tubs compares the options.

Planning a new tub or swim spa?

If you’re building from scratch, plan the heat pump in from the start: a plinth, the circulation line, insulation and the cable route. My DIY hot tub plans and swim spa plans include the plumbing layout and a parts list.

FAQs

What’s the difference between the Vian C5 and the C5 Plus?

The C5 is an on/off heat pump rated down to -5°C. The C5 Plus is a full DC inverter rated to -10°C, with WiFi, a cooling mode and a higher COP when it’s holding temperature.

Will a Vian Power heat pump work in winter?

Yes. The Plus models are rated to -10°C, and Vian publishes COPs down to that temperature (about 2.5–3.6 for the S7 Plus). Output drops in the cold, so heat-ups take longer.

Which Vian heat pump do I need for a hot tub?

For most hot tubs, the S7 Plus. The C5 Plus suits smaller tubs, and the S9 Plus suits larger tubs and swim spas. Check that your pump gives the flow the model needs.

Can I power a Vian heat pump from my spa pack?

Vian’s installation notes say it can take its power from the hot tub supply, and many retrofits do this. It’s still electrical work, so have an electrician confirm the supply is adequate and certify the install.

What warranty do Vian heat pumps have?

5 years on the compressor and heat exchanger, and 2 years on other parts. Frost damage from water left in the unit isn’t covered.

Running a Vian heat pump? Tell me how it’s doing 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