Bathroom Fan - Auto Control by Humidity

bathroom_humidity_fan.yaml

blueprint:
  name: Bathroom Fan - Auto Control by Humidity
  description: >
    Automatically turns on a bathroom fan when humidity spikes quickly, and turns it off
    after humidity stabilizes for a set time. Manual overrides are respected. Optionally
    turns off the fan after it's been on for a maximum time if the humidity is also flat.
  domain: automation
  author: Chris Benard (assisted by ChatGPT)

  input:
    humidity_rate_fast:
      name: Fast Humidity Rate Sensor
      description: Derivative sensor with short window (e.g. 2min)
      selector:
        entity:
          domain: sensor

    humidity_rate_slow:
      name: Slow Humidity Rate Sensor
      description: Derivative sensor with long window (e.g. 10min)
      selector:
        entity:
          domain: sensor

    fan:
      name: Fan Entity
      selector:
        entity:
          domain: fan

    spike_threshold:
      name: Spike Rate Threshold (%/min)
      description: Rate of humidity rise that triggers fan (e.g. 0.25)
      default: 0.25
      selector:
        number:
          min: 0.01
          max: 2.0
          step: 0.01
          mode: slider

    flat_threshold:
      name: Flat Rate Threshold (%/min)
      description: Max rate of change considered “flat” (e.g. 0.05)
      default: 0.05
      selector:
        number:
          min: 0.001
          max: 1.0
          step: 0.001
          mode: slider

    flat_duration:
      name: Flat Duration (minutes)
      description: How long the humidity must stay flat before turning off
      default: 30
      selector:
        number:
          min: 1
          max: 180
          step: 1
          unit_of_measurement: minutes

    enable_max_runtime:
      name: Also turn off fan if it’s been on too long and humidity is flat
      default: false
      selector:
        boolean: {}

    max_runtime:
      name: Max Fan Runtime (minutes)
      description: Only applies if the above is checked
      default: 120
      selector:
        number:
          min: 5
          max: 1440
          step: 1
          unit_of_measurement: minutes

mode: restart

trigger:
  - id: humidity_spike
    platform: numeric_state
    entity_id: !input humidity_rate_fast
    above: !input spike_threshold

  - id: fan_on_too_long
    platform: state
    entity_id: !input fan
    to: "on"
    for:
      minutes: !input max_runtime
    enabled: !input enable_max_runtime

action:
  - if:
      - condition: trigger
        id: humidity_spike
    then:
      - service: fan.turn_on
        target:
          entity_id: !input fan

  - variables:
      flat_threshold_value: !input flat_threshold
      humidity_rate_slow_entity: !input humidity_rate_slow
      flat_duration_value: !input flat_duration

  - wait_for_trigger:
    - platform: template
      value_template: >
        {% set rate = states(humidity_rate_slow_entity) | float(0) %}
        {{ rate | abs < flat_threshold_value | float }}
      for:
        minutes: "{{ flat_duration_value | int }}"

  - condition: state
    entity_id: !input fan
    state: "on"

  - service: fan.turn_off
    target:
      entity_id: !input fan