Case study · heat pump comparison
Both are R290 monobloc heat pumps reaching flow temperatures up to 70°C, and both have a floor-standing version with a built-in 190-litre cylinder (the 151-A and 252-A). The Vitocal 150-A is Viessmann’s most popular domestic range in the UK, from 4 to 16kW. The 250-A is the premium step up, with a higher quoted efficiency and a top result in a German consumer test, but check UK availability with your installer first.
Viessmann makes several air source heat pumps, and the Vitocal 150-A and 250-A are a natural pair to compare. They share a lot: a monobloc design, the natural refrigerant R290 and flow temperatures up to 70°C. The differences are in positioning, efficiency and availability. For the full range, see our Viessmann brand page, or compare Viessmann with Vaillant in Vaillant aroTHERM plus vs Viessmann Vitocal 250-A. The heat pump hub covers every brand we feature.
Vitocal 150-A and 151-A
Viessmann launched the Vitocal 150-A and 151-A in the UK in 2022 as monobloc air source heat pumps, first in 10, 13 and 16kW, then added 4, 6 and 8kW versions in 2023. Both use R290, which has a global warming potential of just 0.02, and reach flow temperatures up to 70°C. Viessmann describes the 150-A and 151-A as its most popular domestic air source heat pump range.
The 150-A has a wall-mounted indoor unit, so it works with a separate hot water cylinder; Viessmann says an existing cylinder may be kept, depending on its coil size and other factors. The 151-A is floor-standing with an integral 190-litre cylinder. Viessmann’s Hydro AutoControl function helps the heat pump fit into existing heating systems, and it says existing radiators may be kept depending on the home’s heat loss. For the 6kW outdoor unit, Viessmann quotes a sound pressure level of 33.5 dB(A) at three metres, measured against one wall in standard heating mode.
Vitocal 250-A and 252-A
The Vitocal 250-A is Viessmann’s premium monobloc, with the complete refrigerant circuit in the outdoor unit. It also uses R290 and reaches 70°C at outdoor temperatures down to -10°C. Viessmann launched it with outputs from 2.6 to 13.4kW, later extending the range to 18.5kW in Europe. The floor-standing Vitocal 252-A adds an integral 190-litre cylinder, and Hydro AutoControl features here too.
Viessmann reports that Stiftung Warentest, Germany’s consumer testing body, named the 250-A the clear winner in its 2023 test of air-to-water heat pumps, with an overall grade of GOOD (2.1). It was the only model in that test to use less than 5,000kWh of electricity a year in the test’s model home.
Availability
This is the most important practical difference. Viessmann’s UK news centres on the 150-A and 151-A, which UK distributors stock in full, along with the Vitocal 200-A ie launched in June 2026 (R290, flow up to 75°C, 4 to 12kW) and the Vitocal 250-A Pro, a 40kW model for larger and commercial buildings. We couldn’t confirm that the domestic 250-A is currently sold through Viessmann UK, so ask your installer whether they can supply it and which sizes are available.
Key differences
In Viessmann’s European launch material, the 250-A is quoted at a coefficient of performance of up to 5.4 at A7/W35 (EN 14511), against up to 5.0 for the 150-A at the same test point. That suggests the 250-A has the edge on efficiency, although your real-world results depend on the design, flow temperature and how the system is controlled.
The 150-A range runs up to 16kW in the UK, with single-phase models plus three-phase options from 10 to 16kW. As the premium model, the 250-A is positioned above it, so ask your installer to quote both where possible and decide whether the difference is worth it for your home.
Whichever model you choose, the grant is the same. In England and Wales the Boiler Upgrade Scheme gives £7,500 towards an air source heat pump, or £9,000 for off-gas-grid homes replacing oil or LPG until March 2027. Your installer confirms the model qualifies and applies on your behalf. In Scotland, Home Energy Scotland grants apply instead. Our grant guide has the details.
Vitocal 150-A vs 250-A compared
Which should you choose?
Choose the Vitocal 150-A or 151-A if:
- You want Viessmann’s established UK range with good stock availability
- Your home needs anything from 4 to 16kW
- You’d like a built-in 190-litre cylinder (151-A) to save space
- You want a well-established all-rounder
Choose the Vitocal 250-A or 252-A if:
- Your installer can supply it in the size you need
- You want the higher quoted efficiency
- An independent consumer test result matters to you
Comparing Viessmann with other brands? See Vaillant aroTHERM plus vs Worcester Bosch Compress 5800i, and read monobloc vs split heat pumps if you’re unsure which design suits your home. Our Vaillant, Ideal and Worcester Bosch pages cover the alternatives.
Frequently asked questions
What is the difference between the Vitocal 150-A and 151-A?
The difference is the indoor unit. The 150-A has a wall-mounted indoor unit and works with a separate cylinder, while the 151-A is floor-standing with an integral 190-litre hot water cylinder.
Can my installer supply the Vitocal 250-A?
We couldn’t confirm it through Viessmann UK, whose recent news focuses on the 150-A and 151-A, the 200-A ie and the commercial 250-A Pro. Ask your installer whether they can supply the domestic 250-A.
Can the Vitocal 150-A work with my existing radiators?
Often, yes. Viessmann says existing radiators may be kept depending on the home’s heat loss, which the installer has to calculate. Some rooms may need larger radiators so the heat pump can run efficiently.
What is the Vitocal 250-A Pro?
It’s a 40kW R290 heat pump for larger properties, public sector buildings and small to mid-scale commercial sites. It needs a three-phase supply and reaches flow temperatures up to 70°C.
Our recommended installer for your area can tell you which Viessmann heat pumps they can supply and which size suits your home.
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