Air to water heat pump: 1.TUV efficiency certification ... to water heat pump :AW10/L,AW13/LNormal air to water heat pump can work at above -10 degrees ,Low temperature air to water heat pump can work ... hot water pump: Wilo water pump is optionalElectric heater: 3KW ,6KW,9KW is optionalAIR TO WATER HEAT ... accurately, SCHNEIDER electronic parts make the unit work safely ,etc ;If you have any requirements ...