The most cost-effective choice.
Operated with an outdoor unit, which transports heat from the outdoor air to the indoor air heat exchanger.
The most efficient for 50-70 m2 during the outdoor temperature is +12...-20°С. (The heat pump). Provides the best operational efficiency during the outdoor temperature +6°С and higher or in case of outdoor temperature -5...-15°С (when the air humidity becomes lower and the frosting becomes lower too due to the better heat exchanging.
Average efficiency: 1 kW of electric power produces 3 kW of heating power.
In case of outdoor temperature lower -15°С its efficiency is become much lower and some additional heating sources is recommended to keep comfortable temperature conditions.
Allowing to cool apartments during hot summer season as usual air conditioner.