I've not really noticed an impact from heating and air con Per Se, but it has to be said that cold weather generally reduces the available range. I get around 3.6m/KWh when the weather's very cold (around 0C) but more like 4m/KWh when it's a bit warmer. I've only had the car since December 15th though so can't comment on how much more I'll get when temps are up around 20C.

Tim H.
1986 4/4 VVTi Sport, 2002 LR Defender, 2022 Mini Cooper SE