[Feature Request] - External Humidity Sensor Support

[BTopbas]

Feature Request: External Humidity Sensor Support

Summary

I would like to be able to assign an external humidity sensor to a Versatile Thermostat entity so that current_humidity is reported from that sensor rather than (or in addition to) the underlying climate entity.

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Motivation

In over_climate mode, current_humidity is currently read directly from the underlying climate entity (e.g. a heat pump or AC unit). However, many users have a dedicated humidity sensor placed in a more representative location (e.g. center of the room), which provides a more accurate reading.

This is already the pattern used for sensor_entity_id (room temperature) and external_temp_sensor_entity_id (outdoor temperature) — a dedicated sensor takes precedence over the underlying entity's reported value.

Additionally, many climate devices (e.g. simple IR-controlled AC units, radiator valves, or third-party integrations) do not expose a humidity value at all. In these cases, current_humidity is always None and there is currently no way to populate it from an external source.

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Proposed Behavior

• Add a new optional config field: humidity_sensor_entity_id
• If configured, current_humidity should return the value from this sensor
• If not configured, fall back to the existing behavior (read from underlying climate entity)
• The value should be exposed as the standard HA current_humidity attribute so it is visible in:
  • The Lovelace thermostat card
  • Apple Home / HomeKit (CurrentRelativeHumidity characteristic)
  • Any other integration that reads the standard ClimateEntity attribute

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Implementation Notes

I have already implemented this locally and it works as expected. The required changes are:

const.py

CONF_HUMIDITY_SENSOR = "humidity_sensor_entity_id"

base_thermostat.py

• Track state changes of the humidity sensor entity
• Read initial value on startup
• Store value in _cur_humidity, _attr_current_humidity, and _humidity

thermostat_climate.py

• Override current_humidity to prefer the external sensor when configured, falling back to underlying_entity(0).current_humidity otherwise

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Use Case

• VTherm type: over_climate
• Underlying entity: Heat pump / AC unit
• Desired sensor: Dedicated room humidity sensor
• Goal: Accurate humidity reading in HA thermostat card and Apple Home

[jmcollin78]

Hello, if you have implemented it, the best you can do now is to do a PR so that I will be able to merge it.
Don't forget tests and documentation in your PR.

[BTopbas]

I implemented this feature and have been running it in production for 2 days without any issues.

The humidity value is correctly exposed as the standard HA current_humidity attribute and shows up natively under the climate entity in both the Lovelace thermostat card and Apple Home (HomeKit).

One thing worth noting: the implementation was assisted by an AI agent, so I'd appreciate a careful review of the code before merging. Everything works as expected on my end, but a second pair of eyes on the logic would be very welcome.