I've noticed my mileage in
I've noticed my mileage in the winter (especially colder months) has really declined from ~34 to ~30. This is largely driven by the car running the engine for heat. I often turn off the heat (only use the electric seats) just so I can get the hybrid advantage.
I have the nav system, and on the second info screen, the power & efficiency tab, one can see the state it's in and why. I've seen reasons the motor is running as cold engine, heater setting, acceleration, high speed, low battery, and normal operation.
Basically, the heat reduces fuel economy, and it's not the strongest heater I've seen, but it's a choice if you want to burn gas to stay warm or burn gas to just go places.