The Arctic MIX-120 unit is projected into homes or apartments that are connected to a central heating distribution network. Functions: The Arctic MIX-520 unit is projected into homes or apartments that are connected to a central heating distribution network. Functions:     The AquaHeat Arctic WKW S-4P set with heat-cold delivery can be projected into homes or apartments that are connected to a heat distribution network. In the event of a water leak in the secondary heating system, water damage is limited to a minimum because the primary and secondary heating systems are separated from each other by a heat exchanger. Functions: • Hot tap water. • Control of the secondary heat cold system by means of a mixing arrangement. • Pressure separation between primary and secondary heat and cold system. • Supply heat-cold when requested by an external thermostat.