In many areas today the buses have air conditioners in the summer and compartment heating in the winter, which certainly ads to the comfort.
I often get questions about what the fuel consumption impact is of heaters and air conditioners.
As always it depends a lot on the user and under which conditions the bus is running.
If the air conditioner (AC) is used just a few months, mostly at noon, the impact is limited. However, in Hong Kong for example the power outtake increase in average by 30-50% for the city double deckers on a yearly basis.
A couple of years ago I made a study on the fuel consumption of the heater on a bus-fleet in Sweden. The buses were using standard heaters from November to March, a period of five months. The heater was only used to give additional heat to the passenger compartments. i.e. engine heating in the morning was managed by an electrical ramp system.
Below I present some data that I have gathered from some different studies of larger fleets.
Yearly Average fuel consumption increase in a statistical analysis of large fleets:
AC Central Europe 6%
AC Israel 12%
Heater Finland 10%
Heater Sweden 6%
It essentially means that when the AC is running the fuel consumption is in average increased by about 20% for one bus.
The trick is to use the comfort equipment when required, but no more than that.