This probably isn't the most reliable source, but the infotainment screen on my VW estimates the hourly gas consumption for the climate system. Running on Max

This probably isn't the most reliable source, but the infotainment screen on my VW estimates the hourly gas consumption for the climate system. Running on Max A/C, the screen reads just under 1/8 gal/hr. With the A/C on and with the fans at 50%, consumption is a little less but still around 1/8 gal/hr. Consumption drops too low to get a reading when A/C is off with fans 50%.