In general, [using an air-conditioner for heating is more efficient than a standard electric heater or radiator](https://efficientcoolheat.com/air-conditioning-more-efficient-than-radiators/). But in our home, we keep the windows open all the time, in order to decrease the chance of infection. Is air conditioning (heat pump) still more energy-efficient than an electric heater? If not - what is the most efficient heating method in this situation?
(Note: the outside temperatures are about 5-15 celsius).