What opinions do you have on the temperature of which the air source heat pump will turn off, and the emergency backup heat will turn on? I hear all kinds, between 20-35 degrees. I have a Trane XL14I, with a Trane gas furnace for backup. It is currently set at 30. If needed... house is in northern Montana. Is brand new construction. I prefer the use of the heat pump, it is quiter than when the furnace fires up. Even at 30 degrees outside, the heat pump is not on all the time, and has no problem keeping my house at 71. Thanks in advance for all the input.