Replacing a tasmota socket for a constant W and converting that to kWh

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Welcome.

Look at the Shelly EM3. Not Tasmota, but it does local mqtt without the need for re-flashing.

This is because the power sensor is never updating and to perform the integration the integral sensor needs a time interval.

Add a sensor.time entity to your power sensor. This will update it every minute.

platform: template
sensors:
  total_ventilation_watts:
    entity_id: sensor.time
    value_template: '{{ 13 }}'
    friendly_name: 'Total ventilation Power Use'
    unit_of_measurement: 'W'

Also please format your code correctly. That was a pain in the arse to copy and correct. See point 11 here: How to help us help you - or How to ask a good question