Air source heat pump for house heating 1. -25 DC low temp. use 2. cooling and heating 3. 4.5 COP, R410a 4. CE approved When the a mbient temperature drops to below zero degree in winter, the normal air source heat pump can not run stably due to the system low evaporation temperature, small gas absorption, small system gas flow and unstable, even cause trouble like compressor liquid hammer etc. ...