It gets 20 to 35 below zero here in the winter time. Will this unit work efficiently in these temps?

Thank you for your question. This particular system efficiently heats with outdoor temperatures as low as -13 degrees Fahrenheit. However, we do have units available that heat with outdoor temperatures as low as -31 degrees Fahrenheit, which may suit your particular application better. We also always recommend a back up heating source to be safe in case of the unlikely event that something were to happen to your primary heat source. For assistance in finding a system with lower ambient heating or for any other assistance, please give us a call.