How to create a dummy energy sensor from a switch controlling a heater?

I have a non-energy-monitoring switch that controls a 1300W heater. Is there an easy way to create an energy sensor from the amount of time that the switch is ON each day? Thanks!

Thanks @tom_l. I ended up creating a history_stat sensor to measure the time that the switch is in ON state, and another template sensor to multiply it by 1.3(kW) to get the daily power consumption. Simple but works for my use case. Just in case if any also needs it:

# Sensors.yaml
- platform: history_stats
  name: STDY heater on hours today
  entity_id: switch.stdrm_heater
  state: "on"
  type: time
  start: "{{ now().replace(hour=0, minute=0, second=0) }}"
  end: "{{ now() }}"
# Templates.ysml
- sensor:
    - name: STDY heater today's consumption
      unique_id: stdy_room_heater_today_s_consumption
      unit_of_measurement: "kWh"
      device_class: energy
      state_class: total_increasing
      state: >
        {% set hours = states('sensor.stdy_heater_on_hours_today') | float %}

        {{ (hours * 1.3) | round(2) }}