How much kWh will an electric boiler consume monthly

Room temperature has a significant impact on consumption. E.g. 1°C increase the temperature of the room, increases consumption 6÷7%.
From experience:
4÷5h/day x Pn x 30(days of the month), which for example would be: 4h/day x 9kW x 30 = 1080 kWh / month.
Parameters from the form:
4÷5h / day-the number of effective working hours of the boiler per day
Pn-nominal boiler power
30-the number of days in a month
Note: The amount obtained by the form may fluctuate from month to month depending on the number of operating hours of the boiler per day, which primarily depend on the average outdoor temperature during that month.