How are we heating?

Last updated on January 1st, 2026

In February 2024 we replaced our 31 years old gas based heating system with a modern heat-pump.
See some photographs here.

• Viessmann Vitocal 250-A AWO-M-E-AC 251 .A08
• Viessmann Vitocell 100-E SVWA200L
  • Buffer for heating system water
• Viessmann Vitocell 100-V CVWC250L
  • Buffer for domestic warm water

• 2nd floor via raditors
• 1st floor via raditors
• ground floor via underfloor heating
• basement via raditors

How did it turn out?

The system works pretty well, we are saving ~ 1/2 the monthly costs compared to the gas heating system. Combined with the photovoltaics system this is even much better. Warmwater is also provided by the system at 46°C currently. I integrated some metrics in Grafana and Home Assistant to get an understanding about how the system behaves.
The JAZ (Jahresarbeitszahl) is currently at 4.3, which means we are producing 4.3 times the heat energy out of the electricity consumed by the system.

What I don't like

The system is fine and we stay warm, but some things could be improved.

• Connectivity is only supported via WiFi, despite LAN is right next to it in the basement
• metrics can be fetched via
  • Viessmann Cloud API. very unstable, small dataset
  • external CAN bus locally, requires some effort, see Open3E
• SG-Ready (Smart Grid) only means you can switch between different energy levels via wire. No API, modbus etc. available (yet)

Numbers

We are heating our ~ 130qm home the following way:

• 2nd floor: home office with raditors, some days at 23°C, else 20°C
• 1st floor: 3 rooms, heated with radiators, 22°C
• ground floor: heated with underfloor heating, 23°C

• COP: Ratio of how much thermal energy was produced from the consumed electricity.