Fronius + Viessmann

What Zerofy can do with Fronius and Viessmann

In practice

• Hot water is the simplest heat store: Autopilot can use the hot-water boost of your Viessmann heat pump to heat water in hours with surplus.
• Zerofy can also change the room temperature of your Viessmann heat pump, so space heating can shift into sunny hours.
• A heat pump draws roughly 1–3 kW while running, which a typical Fronius home system (3–10 kW) can cover on sunny days.
• Zerofy gets new Fronius data every 5 minutes. Heat pumps shouldn’t switch often, so set a minimum runtime in Autopilot.
• Zerofy also shows your Fronius battery, so you can see whether surplus goes into the battery or into the heat pump.
• Autopilot uses Viessmann’s one-time hot-water charge. Because Zerofy can also set the hot-water temperature for Viessmann, you can choose how much surplus the cylinder stores: a higher setpoint holds more energy, at the cost of a somewhat lower heat pump efficiency.
• The Zerofy integration for Viessmann is in beta.

What Fronius and Viessmann offer on their own

Fronius: The Fronius Ohmpilot feeds surplus into a heating rod (0.3–3 kW single-phase, 0.9–9 kW three-phase) and has a control output for a heat pump with an SG Ready input. GEN24 inverters can also switch an SG Ready input through one of their four digital outputs plus a coupling relay, and Fronius lists direct integrations with heat pumps from IDM, Bosch and NIBE.

Viessmann: Viessmann’s Energy Management on One Base links Vitocal heat pumps, the Vitocharge VX3 battery, the Viessmann Charging Station and hot-water tanks, using an E380CA energy meter; ViCare then shows self-consumption and autarky. Third-party inverters are brought in through the Solar-Log Base Vi gateway, with compatibility per Solar-Log’s component database.

Zerofy connects the two: it reads Fronius production and controls your Viessmann heat pump to match, together with your other devices in one app, with dynamic tariffs and forecast-based Smart mode.

Setting up Fronius and Viessmann in Zerofy

1. Connect Fronius

Zerofy reads your system from Fronius Solar.web through a guest account that you create for Zerofy.

1. Make sure your Fronius inverter is online and shows up in Solar.web.
2. In Solar.web, go to Settings → Permissions and create a new guest account.
3. Add Fronius in Zerofy and log in with the guest account credentials.

Step-by-step guide for Fronius

2. Connect Viessmann

Zerofy connects to the Viessmann cloud with your Viessmann (ViCare) account and shows a Space Heating and a Hot Water Tank device; you can adjust room and hot-water temperature, and Autopilot triggers the hot-water boost.

1. Check that the system runs on Viessmann One Base or has an Optolink interface with a Vitoconnect OPTO2 gateway, and that it is online.
2. In Zerofy, add a Viessmann device.
3. Log in with your Viessmann account credentials and follow the prompts.
4. Enable Autopilot (Solar or Smart mode) for the Hot Water Tank.

Good to know: The Viessmann integration is in beta. Flow/circuit temperature can’t be set from Zerofy, and Autopilot currently steers only the hot-water tank; space-heating control is coming.

Step-by-step guide for Viessmann

3. Turn on Autopilot

In Zerofy, open your Viessmann heat pump, turn on Autopilot and choose Solar – or Smart to also use dynamic tariffs and forecasts. Set the priority, activation threshold and minimum runtime.

Dynamic tariffs

Zerofy can also run your Viessmann heat pump on dynamic electricity prices (EPEX Spot or Nord Pool, e.g. Tibber or aWATTar) or on a fixed time-of-use tariff. Smart mode combines those prices with forecasts of your household consumption and your Fronius solar production.

Learn more about Smart Mode

About Fronius and Viessmann

Fronius – Austrian manufacturer of inverters, welding and battery-charging technology. Homeowners typically have a Primo GEN24 (single-phase, 3–6 kW) or Symo GEN24 (three-phase, 3–10 kW) hybrid inverter, older Primo/Symo SnapINverters, and the Fronius Reserva battery (6.3–15.8 kWh). Monitoring app: Fronius Solar.web.

Viessmann – Viessmann is a German heating manufacturer from Allendorf (Eder). Newer heat pumps such as the Vitocal 250-A and Vitodens boilers run on the Viessmann One Base platform with built-in Wi-Fi; older Vitotronic systems go online through a Vitoconnect gateway. Products: Vitocal 250-A, Vitocal 200-S, Vitodens 200-W/300-W boilers, Vitovalor fuel cells, older systems with Vitotronic controllers.

Manufacturer information last checked: October 2026.

All devices that work with Fronius