AC has a negligible impact on consumption. Unsurprisingly, heat pumps are efficient ways to move heat, and the temperature differentials are never very high (at most, 30-40F). Heating is a much bigger issue, since temperature differentials can be much higher (as much as 100F delta in truly cold climates, or 50-60F deltas in more normal climates), and the cooling effect of wind works against you (instead of for you, in the case of AC).
