Folks,
The Prius gets it's heating from the engine just like other cars. It's advantage is the hybrid controls that shut off the engine when it reaches temperature until you pull too much heat from the engine to start again.
As for A/C on the Prius it is run by electric off the hybrid high voltage battery. You leave the A/C on and when you have used enough of the high voltage battery the engine will start to recharge the high voltage battery.
On my way to the RTR this year it was 14 deg just south of Harrisburg, PA and I stopped in a rest area and set the temp to 65 and the engine ran for a minute every 5 minutes. I slept well.
Recently in southern AZ when it was in the 90's I would run the A/C when I went in long hikes. I set the temp to 78 and the engine would run about a minute every 10 minutes. I was helping my compressor fridge as inside my Prius it would get to 120 and this is not helpful for my compressor.
Brent