I have a Trane Weathertron (BAYSTAT240A) thermostat for my Trane heat pump. When the outside temp is nears 35 degrees the heat pump struggles. There is an Emergency "On" switch which I guess turns on the electric auxiliary coils and disables the heat pump. If that is accurate, does the cost of operation increase substantially? In normal operation around 35 degrees, the unit seems to run most of the time--a five minute break per 20 minutes of operation. Is the efficiency of the emergency heat greater than this almost full time running in heat pump mode?