Thermostat Proxy (Home Assistant)

A Home Assistant custom integration that lets you expose a virtual climate entity which mirrors a real thermostat but lets you pick any temperature sensor to act as the “current temperature”. When you change the virtual target temperature, the integration calculates the difference between the selected sensor and the requested set point, then offsets the real thermostat so it behaves as if it were reading the chosen sensor.

Installation via HACS

Features

• Wraps an existing climate entity; copies all of its attributes for dashboards/automations.
• Supports any number of temperature sensors. Each named sensor becomes a preset_mode, so changing the preset swaps the active sensor.
• Falls back to the real thermostat’s current_temperature whenever the selected sensor is unknown or unavailable.
• climate.set_temperature service adjusts the linked thermostat by the delta between the selected sensor reading and your requested temperature.
• Exposes helper attributes: active sensor, sensor entity id, real current temperature, and the last real target temperature.
• Remembers the previously selected sensor/target temperature across restarts and surfaces an unavailable_entities attribute so you can monitor unhealthy dependencies.
• Always adds a built-in preset for the wrapped thermostat’s own temperature reading (named Physical Entity by default, but you can rename it during setup) so you can revert or set it as the default sensor.
• If someone changes the physical thermostat directly, the proxy automatically switches to the physical preset and logs the change in Home Assistant's logbook.
• "Overdrive" logic: If the remote sensor hasn't reached the target but the physical thermostat thinks it's done (e.g. goes "Idle"), the proxy will temporarily offset the real target by an additional degree to force the HVAC to keep running until the remote sensor is satisfied.
• Fan Mode Support: Fully proxies the real thermostat's fan modes. You can control the fan (Auto/On/Low/etc.) seamlessly through the proxy entity.
• User Log Attribution: Logbook entries for target temperature or preset changes will show which user performed the action.
• Default sensor selector includes a "Last active sensor" option (during setup or in options) so the proxy resumes with the most recently selected sensor instead of the configured default.

How It Works

• current_temperature reflects the selected sensor. If its state is unknown/unavailable, the entity reports the real thermostat’s own temperature.
• preset_modes is populated with the configured sensor names. Calling climate.set_preset_mode switches the sensor.
• When you call climate.set_temperature on the custom entity, it calculates delta = requested_temp - displayed_current_temp and then sets the real thermostat to real_current_temp + delta. A two-degree increase relative to the virtual sensor becomes a two-degree increase on the physical thermostat, for example.
• Overdrive: If the virtual target is not met (e.g., set to 70, sensor reads 69), but the physical thermostat (satisfied at its own location) goes Idle, the integration detects this "Stall". It then applies a +1° (or -1° for cooling) "Overdrive" offset to the physical thermostat's target to force it to run. This offset sticks until the virtual target is met or the system is no longer stalled.
• Requested targets are clamped to the physical thermostat’s min_temp, max_temp, and target_temp_step so automations can’t push the hardware outside its supported range.
• If the physical thermostat’s target changes outside of this integration, the proxy moves to the physical preset and aligns its virtual target with the real target.
• All attributes from the physical thermostat are forwarded as extra attributes, alongside:
  • active_sensor
  • active_sensor_entity_id
  • real_current_temperature
  • real_target_temperature
  • sensor_options
  • unavailable_entities

Automations / Service Examples

Switch the active sensor (preset):

action: climate.set_preset_mode
target:
  entity_id: climate.living_room_proxy
data:
  preset_mode: Kitchen

Set a sensor-based target temperature:

action: climate.set_temperature
target:
  entity_id: climate.living_room_proxy
data:
  temperature: 73

The integration will take the currently selected sensor’s temperature, compare it to the requested value, and offset the real thermostat accordingly.

Automatically move the proxy to the kitchen sensor whenever the fireplace is running so the extra heat doesn’t throw off the default thermostat, then fall back to the physical preset (renamed if you customized it) once the fire is off:

alias: Thermostat Mode Adjust
description: Automatically adjust thermostat proxy preset mode.
triggers:
  - trigger: state
    entity_id:
      - switch.fireplace
    to:
      - "on"
    id: Fireplace On
    from:
      - "off"
  - trigger: state
    entity_id:
      - switch.fireplace
    to:
      - "off"
    id: Fireplace Off
    from:
      - "on"
conditions: []
actions:
  - choose:
      - conditions:
          - condition: trigger
            id:
              - Fireplace On
        sequence:
          - action: climate.set_preset_mode
            data:
              preset_mode: Kitchen
            target:
              entity_id: climate.custom_thermostat
      - conditions:
          - condition: trigger
            id:
              - Fireplace Off
        sequence:
          - action: climate.set_preset_mode
            data:
              preset_mode: Physical Entity
            target:
              entity_id: climate.custom_thermostat
mode: single

Limitations / Notes

• The component assumes a single target temperature (heat, cool, or auto with a shared set point). Dual set points (target_temp_low / target_temp_high) are not supported.
• Because Home Assistant does not expose the real thermostat’s precision/step directly, changes to current_temperature or the linked thermostat may momentarily desync the displayed target temperature if another integration changes the physical thermostat. The entity exposes the real target temperature as an attribute so you can reconcile differences.
• Manual changes made directly on the physical thermostat will switch the proxy to the physical preset and align the virtual target with the real set point while recording a logbook entry.
• If you pick a specific default sensor instead of "Last active sensor", the proxy will fall back to that default after a restart even if you had switched to a different preset earlier.
• This integration does not use humidity data for its core logic (e.g., temperature control), but it does expose the underlying thermostat's humidity reading as a real_current_humidity attribute for visibility.

Contributing

Contributions are welcome! Feel free to create a new branch and submit pull a request!