The overnight low last night was -32F and at 11:00AM this morning it is still -20F. The Geo unit ran on the first and second stage most of the night. With a setting of 70F on the thermostat, the actual inside temperature never dropped below 69F. This means that the third electric resistance heating stage may never run. I can't imagine conditions in our locale that could cause the inside temperature to drop to 67.5F degrees (the resistance heating stage set point).
I have some understanding of how the system works. I am still amazed that a whole house can be heated in -32F temperatures by 40 degree pond water!
