[RMcNeal]

I put the electric heater directly below the return ducts for the heat pump/AC. It is drawing air from inside the rig the same way our AC does. I can actually feel it and confirmed with powder and vapor. Without a heater inside, the heat pump freezes up below around 40 degrees. With the heater or fireplace on, it continues to work down into the low 30's and is not frozen.
I was told that the heat pump essentially runs the AC in reverse. Is that not correct?