Electric heater
In order to calculate the capacity of the electric heater, we use a rule of thumb. Globally you can assume about 75 watts per m3.
(To get a temperature of 18oC, you need about 70 watts per cubic meter).
For example, a property with a size of 6x2,2M, an internal height of 2,5M and a total capacity of 33M3. We multiply it by 75 watts, so the required capacity will be: 2.475 watts.