Have a look at how heat pumps work. The difference between cooling and heating is just which end you point inside or outside. For efficiency it only matter wha

Have a look at how heat pumps work. The difference between cooling and heating is just which end you point inside or outside. For efficiency it only matter what the delta-T with the outside environment is. Since that is typically lower when cooling than when heating, it is therefore cheaper. Just look at your power bill.