What is the coldest working temp?

Thank you for your question. This system efficiently heats with outdoor temperatures ranging from 15 degrees Fahrenheit and 75 degrees Fahrenheit. It efficiently cools with outdoor temperatures ranging from 15 degrees Fahrenheit and 115 degrees Fahrenheit. During heating this system has the operation range of 60 to 88; during cooling it has the operation range of 64 to 90. For more assistance, please give us a call.