template:

    - sensor:
        - name: "Average Temp"
          unique_id: 3fe8a884-23ab-4d03-92b2-13e04ca55b18
          unit_of_measurement: "°C"
          device_class: temperature
          state: >
            {% set wz = states('sensor.wz_klima_temperature')|float("unavailable") %}
            {% set bad = states('sensor.bad_klima_temperature')|float("unavailable") %}
            {% set sz = states('sensor.sz_klima_temperature')|float("unavailable") %}
            {% set ug_fl = states('sensor.ug_fl_klima_temperature')|float("unavailable") %}

            {% set t = [wz, bad, sz, ug_fl]|reject('eq', "unavailable")|map('float')|list %}
            {% set qty = t|count %}
            {# only calculate average if at least 1 sensor is not unavailable #}
            {% if qty > 0 %}
            {{ (t|sum/qty)|round(1) }}
            {% endif %}