The problem
Most of Europe’s homes are heated by burning gas or oil. In Germany, the large majority of homes are still heated with gas or oil. Switching to heat pumps is the main way to cut those emissions, but many owners worry that a heat pump will only work in a new, well-insulated house with underfloor heating.
Older houses often have small radiators designed for water at 60 to 70 °C. Early heat pumps struggled to reach those temperatures efficiently, especially in winter. There was also a refrigerant problem: many heat pumps used fluorinated gases with a high global warming potential, which the EU is phasing down.
The product
The Vitocal 250-A is an outdoor monobloc air-to-water heat pump. It draws heat from outside air and delivers hot water for radiators, underfloor heating and taps. The refrigerant circuit is sealed inside the outdoor unit, so installers do not handle refrigerant on site (Viessmann).
Key specifications from Viessmann’s German product page:
- Output: 2.6 to 18.5 kW in the retrofit version.
- Flow temperature: up to 70 °C, still reached at an outdoor temperature of minus 10 °C.
- Efficiency: COP up to 5.5 at A7/W35; label A+++.
- Refrigerant: R290 (propane), with a global warming potential close to zero.
- Versions: a split indoor unit, or the Compact version with an integrated 190 litre hot water tank.
Viessmann says the 2025 generation is up to 5 dB(A) quieter, which shrinks the distance needed to the neighbour’s boundary under German noise rules (TA Lärm). For apartment blocks and businesses, the Vitocal 250-A PRO goes up to 39.5 kW, and series production started at Viessmann’s Berlin plant on 17 June 2024 (Viessmann Climate Solutions).
How it works
- Absorb: a fan pulls outside air across an evaporator; the cold propane absorbs heat even when the air is below freezing.
- Compress: a variable-speed compressor raises the pressure and temperature of the propane vapour.
- Release: in a heat exchanger, the hot propane passes its heat to the house’s heating water.
- Expand: an electronic valve lowers the pressure and the cycle starts again.
- Control: the unit adjusts its speed to demand, and the app and controller can shift operation to times of cheap or solar electricity.
Propane is flammable, so the system is sealed and holds only a small charge, and the outdoor placement keeps it away from living spaces.
Timeline
| Date | Milestone |
|---|---|
| 29 Apr 2021 | Viessmann announces the Vitocal 25x-A range with R290 and 70 °C flow |
| End 2021 | Market launch |
| 2 Jan 2024 | Carrier completes acquisition of Viessmann Climate Solutions |
| 17 Jun 2024 | Series production of Vitocal 250-A PRO starts in Berlin |
| 2025 | Quieter generation, up to 5 dB(A) lower |
| 10 Jul 2026 | Bundestag passes the Gebäudemodernisierungsgesetz, 323 votes to 271 |
| 29 Jul 2026 | Main rules of the new law take effect |
Impact and numbers
- Market: about 195,000 heating heat pumps were sold in Germany in the first half of 2026, up 40% on a year earlier, according to the BWP and BDH; just under 2 million heat pumps are now installed in the country (BWP).
- Efficiency: a COP of 5.5 means 5.5 kWh of heat for each kWh of electricity under test conditions; real seasonal results in old houses with radiators will be lower.
- Refrigerant: propane avoids high-GWP fluorinated gases and is in line with the EU F-gas phase-down.
- Subsidy: from 21 July 2026 the federal BEG programme covers eligible costs of up to €28,000 for the first home unit, falling by €750 every six months from February 2027 (KfW, BMWE).
Honest caveats. Germany’s rules have changed. The Gebäudemodernisierungsgesetz, passed by the Bundestag on 10 July 2026 by 323 votes to 271 and in force from 29 July, replaced the GEG heating rules (Bundestag, tagesschau). The requirement that new heating systems run on 65% renewable energy is gone, and new gas and oil boilers are allowed again. Instead, fuels must become climate neutral by 2045, with a rising bio share from 2029 and a green gas quota from 2028, details still to be set. So heat pumps must now win on running costs and subsidies rather than law. Viessmann’s own figures are inconsistent: launch material gave the refrigerant GWP as 3, newer pages say 0.02, and the lowest temperature for 70 °C fell from minus 15 °C (2021) to minus 10 °C on the current page. Lab COP values are not what owners see in winter. Viessmann is also now part of US-based Carrier, which bought it for about €12 billion (Viessmann), so “German family firm” no longer applies.
What’s next
Viessmann is pushing quieter, smaller outdoor units that fit tight terraced plots, plus links to rooftop solar and batteries. Carrier wants to use the Viessmann brand to grow in Europe’s residential heating market. The key German date is 1 December 2026, the deadline for the separate law that will set the green gas quota. If gas bills rise as the quota bites, a heat pump that can run old radiators becomes the obvious alternative.
Why it matters for Europe / green buyers
Germany is Europe’s largest heating market, and its law change will be watched by other countries implementing the recast Energy Performance of Buildings Directive, which aims to phase out fossil fuel boilers by 2040. The R290 trend matters too: propane heat pumps are now mainstream, which reduces the risk of buying a unit with a refrigerant facing future restrictions. For buyers, the questions to ask are: what flow temperature do my radiators really need, what is the seasonal efficiency (SCOP) at that temperature, how loud is the unit at my neighbour’s window, and which BEG funding can I still claim?
India has little need for space heating outside the Himalayan states, and no Indian Vitocal 250-A listing was found. But air-to-water heat pumps for hot water are growing in hotels, hospitals and apartment blocks, where they can replace electric geysers and diesel boilers. The same move to natural refrigerants such as propane and CO2 is under way there, supported by India’s Kigali Amendment commitments on HFCs.
Sources & image credits
- Viessmann, “Vitocal 250-A: Luft/Wasser-Wärmepumpe zum Modernisieren” (product page): https://www.viessmann.de/de/produkte/waermepumpe/vitocal-250-a.html
- Viessmann Climate Solutions, “Production for Vitocal 250-A PRO launched in Berlin” (17 Jun 2024): https://www.viessmann-climatesolutions.com/en/newsroom/solution-offering/production-for-vitocal-250-a-pro-launched-in-berlin.html
- Viessmann Climate Solutions, “Carrier completes acquisition of Viessmann Climate Solutions” (2 Jan 2024): https://www.viessmann-climatesolutions.com/en/newsroom/company/carrier-completes-acquisition-of-viessmann-climate-solutions.html
- Deutscher Bundestag, roll-call vote on the Gebäudemodernisierungsgesetz (10 Jul 2026): https://www.bundestag.de/parlament/plenum/abstimmung/abstimmung/?id=1018
- tagesschau.de, “Bundestag und Bundesrat stimmen für Gebäudemodernisierungsgesetz” (Jul 2026): https://www.tagesschau.de/inland/innenpolitik/bundestag-gebaeude-modernisierung-gesetz-100.html
- BWP, “Wärmepumpen-Absatz wächst im ersten Halbjahr auf 195.000 Anlagen” (6 Aug 2026): https://www.waermepumpe.de/presse/pressemitteilungen/details/waermepumpen-absatz-waechst-im-ersten-halbjahr-auf-195000-anlagen/
- KfW, “Die neue Bundesförderung für effiziente Gebäude startet jetzt” (Jul 2026): https://www.kfw.de/%C3%9Cber-die-KfW/Newsroom/Aktuelles/Pressemitteilungen-Details_901760.html
- BMWE, FAQ BEG 3.3, “Welche Höchstgrenzen förderfähiger Ausgaben gelten beim Heizungstausch?”: https://www.energiewechsel.de/KAENEF/Redaktion/DE/FAQ/FAQ-Uebersicht/BEG/faq-beg-03-03.html
Images:
- “Newly installed heat pump Viessmann Energycal AW PRO AT 70.2, November 2021, Tomaszów Mazowiecki, Sikorskiego Street” by WrS.tm.pl, public domain, via Wikimedia Commons: https://commons.wikimedia.org/wiki/File:Newly_installed_heat_pump_Viessmann_Energycal_AW_PRO_AT_70.2,_November_2021,_Tomasz%C3%B3w_Mazowiecki,_Sikorskiego_Street.jpg
