It is the end of February and they are singing a sweet duet! They have a small photo-voltaic panel that powers the fan, so no outside energy is needed. As long as I have the sun shining I can get heat.
These units are really good in the transitional seasons of Spring and Fall. Some days the temperature will get up to 80 degrees in the house just from these panels
I purposely set my thermostat to 80 degrees as the upper limit. When you are trying to be earth friendly you have to be willing to change your lifestyle somewhat. We just get used to indoor temperature swings that mimic the outdoor earth cycles.