FoxESS + CTA

What Zerofy can do with FoxESS and CTA

In practice

• When there’s enough surplus, Zerofy switches the relay and the heat pump receives the SG Ready signal. How it reacts – for example by heating the hot-water tank to a higher temperature – is set in the heat pump’s own controller.
• A heat pump draws roughly 1–3 kW while running, which a typical FoxESS home system (2.5–15 kW) can cover on sunny days.
• Zerofy gets new FoxESS data every 5 minutes. Heat pumps shouldn’t switch often, so set a minimum runtime in Autopilot.
• Zerofy also shows your FoxESS battery, so you can see whether surplus goes into the battery or into the heat pump.
• CTA’s own tip for SG Ready operation: if rooms get too warm or too cold, change the upper temperature limit by 1 °C at a time and leave it for one to two days before adjusting again; agree the values with your heating installer.

What FoxESS and CTA offer on their own

FoxESS: FoxESS has its own R290 heat pumps (HP Series monobloc, HP BOX hydro module), controlled in FoxCloud 2.0, which lists a solar heating feature. The three-phase H3 Pro can switch an SG Ready heat pump through its dry contacts when feed-in exceeds a set start power.

CTA: For PV self-consumption, CTA connects its heat pumps to external energy management systems via a PV input, SG Ready or Modbus (Optiheat and Aeroheat). CTA publishes SG Ready instructions per model and a compatibility list for the Swiss Solar Manager gateway (Modbus TCP/RTU).

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

Setting up FoxESS and CTA in Zerofy

1. Connect FoxESS

Zerofy connects to the FoxESS cloud: you log in with your FoxESS Cloud account and authorize access on FoxESS’s own screen.

1. Make sure your inverter is online and registered in the FoxESS Cloud app.
2. In Zerofy, choose FoxESS and log in with the FoxESS Cloud owner account.
3. Confirm your devices on the FoxESS authorization screen.

Good to know: Use the owner account of the device. Installer and agent accounts don’t own the devices, so FoxESS shows “No Devices” and the connection fails.

Step-by-step guide for FoxESS

2. Connect CTA

The Zerofy docs have no CTA-specific guide; the documented way to control a CTA heat pump is Zerofy’s SG Ready integration, with a smart relay such as a Shelly wired to the heat pump’s SG Ready inputs.

1. Check in CTA’s SG Ready compatibility list that your model and controller (Optiplus, Optiplus 3, Aeroplus 2.0/2.1) are listed.
2. Have an electrician wire a smart relay (e.g. Shelly) to the heat pump’s SG Ready inputs.
3. Add the relay to Zerofy and configure it as SG Ready controller.

Good to know: CTA marks Optiheat Inverta units and several Aeroheat models as needing a software or controller update for SG Ready. For older or unlisted units, CTA says integration can mean extra cost, e.g. a controller replacement.

Step-by-step guide for CTA

3. Turn on Autopilot

In Zerofy, open your CTA 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 CTA 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 FoxESS solar production.

Learn more about Smart Mode

About FoxESS and CTA

FoxESS – Fox ESS is a Chinese inverter and storage maker founded in 2019 and headquartered in Wenzhou. Homes typically have the single-phase H1/AC1 (2.5–6 kW) or KH (7–10.5 kW) hybrid inverters or the three-phase H3 Smart (5–15 kW), with EP, EQ or ECS batteries. Monitoring app: FoxCloud 2.0.

CTA – CTA AG is a Swiss manufacturer of heat pumps and cooling machines, with production at its headquarters in Münsingen near Bern. Its home range covers Optiheat ground-source and water-source heat pumps and Aeroheat air-source heat pumps. Products: Optiheat (brine/water and water/water), Optiheat Inverta, Aeroheat (air/water, indoor and outdoor units), Aeroheat Inverta.

Manufacturer information last checked: October 2026.

All devices that work with FoxESS