Viessmann vs Vaillant: Which Heat Pump Is Better?
Viessmann’s Vitocal 150-A and Vaillant’s aroTHERM plus are R290 heat pumps from two German heating brands that many UK installers already know from their boilers. On published data they are very close on efficiency; the differences are flow temperature, sizes, indoor units and how each extends its warranty.
- Manufacturer datasheets checked 25 October 2026
- Published data, not paid placement
- Independent UK research
Quick verdict
See the specificationsVery close on paper, with Viessmann’s 8kW slightly ahead of Vaillant’s 7kW on seasonal efficiency. Vaillant reaches a higher maximum flow temperature (75°C against 70°C) and offers a smaller 3.5kW size; Viessmann offers an integrated 190-litre cylinder unit and larger 13 and 16kW sizes. Your installer’s experience with either brand will matter more than the gap between them.
Choose Viessmann Vitocal 150-A if…
- You want an all-in-one indoor unit: the Vitocal 151-A has a 190-litre cylinder built in
- Your home needs a larger output: sizes go up to 16kW
- You like a 7-inch touchscreen on the unit as well as the ViCare app
- Your installer is a Viessmann specialist
Choose Vaillant aroTHERM plus if…
- Some rooms need hotter radiators: aroTHERM plus reaches 75°C
- Your home needs a very small output: sizes start at 3.5kW
- You want a Cover & Care plan with up to 10 years’ cover including servicing
- Your installer is experienced with Vaillant and its uniTOWER
Viessmann Vitocal 150-A vs Vaillant aroTHERM plus side by side
Both are monobloc-style heat pumps: the R290 refrigerant stays sealed in the outdoor unit and water pipes run into the house.
Viessmann
Viessmann Vitocal 150-A (R290)
- 4, 6, 8, 10, 13 and 16kW models
- Up to 70°C flow temperature down to -10°C outside
- Vitocal 151-A version has a 190-litre cylinder built in
- 7-inch colour touchscreen and ViCare app
Best suited to: homes short on space that suit an integrated indoor unit, and larger homes needing 13 or 16kW.
Vaillant
Vaillant aroTHERM plus (R290)
- 3.5, 5, 7, 10 and 12kW models
- Up to 75°C flow temperature
- Heats down to -25°C outside
- Pairs with Vaillant’s uniTOWER indoor unit or a separate cylinder
Best suited to: small, well-insulated homes and flats, and homes where a few rooms need hotter radiators.
Product photos are for illustration and may not show the exact model compared.
Specifications compared
We compared the closest sizes each brand makes: Viessmann’s 8kW (Vitocal 150-A08) and Vaillant’s 7kW (VWL 75/6). Viessmann publishes seasonal efficiency (ηs) rather than SCOP, so we converted it using the standard EN 14825 formula; Vaillant’s figures are from its aroTHERM plus installer’s quick guide. Checked 25 October 2026. We have not tested these heat pumps ourselves.
| Specification | Viessmann Vitocal 150-A | Vaillant aroTHERM plus |
|---|---|---|
| Model compared | 8kW (Vitocal 150-A08) | 7kW (VWL 75/6) |
| Refrigerant | R290 (propane) | R290 (propane) |
| Range of sizes | 4, 6, 8, 10, 13 and 16kW | 3.5, 5, 7, 10 and 12kW |
| SCOP at 35°C (underfloor) | 4.45 (A+++) | 4.36 (A+++) |
| SCOP at 55°C (radiators) | 3.50 (A++) | 3.39 (A++) |
| Maximum flow temperature | 70°C (down to -10°C outside) | 75°C |
| Lowest outdoor temperature | Not stated in the brochure we checked | -25°C |
| Sound power (heating) | 51 dB(A) (night mode) | 55 dB(A) (A7/W55) |
| App | ViCare | myVAILLANT |
| Longest manufacturer warranty | 2 years from delivery; paid extensions if the installer registers it within 30 days (details) | 2 years as standard; 5, 7 or 10 years through a paid Cover & Care plan that includes servicing (details) |
Ask installers which of these brands they fit, and get both quoted if you can. A good installer will size the heat pump from a room-by-room heat loss calculation, not from the size of your old boiler.
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Efficiency and winter performance
At 55°C, the radiator temperature most older homes need on cold days, Viessmann’s 8kW Vitocal 150-A works out at a SCOP of about 3.50 against 3.39 for Vaillant’s 7kW aroTHERM plus. That gap is small enough that system design will matter far more.
At 35°C, typical of underfloor heating, the figures are about 4.45 for Viessmann and 4.36 for Vaillant. Viessmann publishes seasonal efficiency as ηs (175% at 35°C and 137% at 55°C for the 8kW), which we have converted to SCOP so the two can be compared.
For radiators, Vaillant’s 75°C maximum flow temperature gives a little more headroom than Viessmann’s 70°C, which Viessmann quotes down to -10°C outside. Most well-designed systems run far cooler than either for most of the year.
These are lab ratings for an average European climate, on slightly different sizes. In a real home, good design matters far more: a heat pump running at a low flow temperature with weather compensation will beat a better-rated one that is set up badly. Our guide to heat pumps in winter explains what happens on the coldest days.
Noise
The published noise figures are not measured the same way, so we cannot say which is quieter. Viessmann quotes 51 dB(A) sound power for its 8kW in night mode; Vaillant quotes 55 dB(A) for its 7kW at A7/W55.
Viessmann’s product page gives 51 to 55 dB(A) across the range. Ask any installer quoting either brand for the sound power figure they used in the MCS noise assessment for your home.
Sound power is measured at the unit itself. What you and your neighbours hear depends on distance, walls, fences and how hard the heat pump is working. Your installer must check the position against the MCS noise assessment for permitted development, so ask to see that calculation.
Hot water and indoor units
Both have an indoor unit with the cylinder built in: Viessmann’s Vitocal 151-A with a 190-litre cylinder, and Vaillant’s uniTOWER.
The standard Vitocal 150-A has a small 16-litre buffer and works with a separate cylinder. Vaillant also pairs the aroTHERM plus with separate cylinders and a wall-hung hydraulic module.
Either way you will normally need a hot water cylinder. If you are coming from a combi boiler, our combi to heat pump guide explains how to find the space. Your installer will also set a regular legionella cycle.
Controls and apps
Viessmann uses the ViCare app and a 7-inch colour touchscreen on the unit; Vaillant uses the myVAILLANT app.
Both let you change temperatures and schedules remotely. Viessmann’s installers use its ViGuide tool to monitor and adjust the system.
We compare the apps in more depth in our best heat pump apps guide.
Warranty and installer network
Both start at 2 years. Viessmann’s runs from delivery and can be extended for a fee if the installer registers the installation within 30 days. Vaillant extends to 5, 7 or 10 years through a paid Cover & Care plan that includes annual servicing.
Vaillant’s Cover & Care plans cost £295–£312 a year when we checked on 23 October 2026, and the heat pump must be under 18 months old to join. Both brands require an annual service to keep the warranty valid.
Registration deadlines and servicing conditions apply. Our heat pump warranties guide sets them out brand by brand. In practice, the cover you get depends on the installer, so ask about their accreditation before comparing quotes.
Cost: what changes the price
Neither brand publishes UK installed prices, and the brand is rarely the biggest factor in what you pay. The Energy Saving Trust puts a typical air source heat pump installation at around £12,000 before grants, and the Boiler Upgrade Scheme takes £7,500 off for most eligible homes in England and Wales.
What actually moves the quote is the heat pump size your heat loss survey calls for, the cylinder, how many radiators need upgrading, pipework and electrical work. Installers also get different trade prices from different brands, so the same home can be quoted very differently for Viessmann and Vaillant. The only reliable way to compare is to get quotes for both from MCS-certified installers, using the same heat loss figures. Our air source heat pump cost guide and grants guide cover the detail.
Which suits your home?
Older home with radiators
Vaillant’s 75°C maximum gives more headroom for a few small radiators. Viessmann is slightly more efficient at 55°C on paper.
Small home or flat
Vaillant’s 3.5kW aroTHERM plus suits very low heat loss; Viessmann starts at 4kW.
No airing cupboard
Viessmann’s Vitocal 151-A and Vaillant’s uniTOWER both put the cylinder in the indoor unit. Compare the footprints.
Read what size heat pump do I need and get a proper heat loss survey. An oversized heat pump costs more and can short-cycle, which hurts efficiency.
Questions to ask installers
- Which of these two brands do you fit, and are you accredited with either one?
- What output does my heat loss calculation call for, and which model size would you fit?
- What is the SCOP at the flow temperature you are designing for, not just at 35°C?
- Where will the outdoor unit go, and does it pass the MCS noise assessment for that spot?
- Which cylinder or indoor unit would you use, and how much floor space does it need?
- How many years of manufacturer warranty will I actually get, and who registers it?
- Will you set up weather compensation and show me how to use the app before you leave?
Frequently asked questions
Is Viessmann or Vaillant better?
On published data they are very close. Viessmann’s 8kW is slightly more efficient than Vaillant’s 7kW; Vaillant reaches a higher flow temperature and has a smaller size. The installer’s experience with the brand usually matters more.
Which is quieter, Viessmann or Vaillant?
We cannot say from published data because the figures are measured differently: Viessmann quotes 51 dB(A) for its 8kW in night mode, and Vaillant 55 dB(A) for its 7kW at A7/W55. Ask your installer for the figure used in your noise assessment.
How long is the warranty on Viessmann and Vaillant heat pumps?
Both give 2 years as standard. Viessmann offers paid extensions if registered within 30 days; Vaillant offers 5, 7 or 10 years through a paid Cover & Care plan. See our warranties guide for the details.
Do both work with existing radiators?
Yes. Vaillant reaches up to 75°C and Viessmann up to 70°C, though both run more efficiently at lower temperatures, so some radiators may still need upgrading.
Can I get the Boiler Upgrade Scheme grant with either brand?
Yes, as long as an MCS-certified installer fits it and your home meets the scheme rules. The grant does not depend on the brand. See our grants guide for eligibility.
Sources and further reading
All sources checked on 25 October 2026. Specifications can change between model updates, so ask your installer for the datasheet of the exact model they quote.
- Viessmann: Vitocal 150-A / 151-A brochure (technical data, July 2023)
- Viessmann: Vitocal 150-A Compact product page
- Viessmann UK: Warranty
- Vaillant: aroTHERM plus installer’s quick guide (technical data)
- Vaillant: aroTHERM plus installation and operating manual
- Vaillant: Heat pump Cover & Care packages
- Energy Saving Trust: Air source heat pumps
- GOV.UK: Apply for the Boiler Upgrade Scheme