12. The heating system shall be capable of providing a volumetric thermal capacity of not less than 0.9 kWh/m3 to the entire part of the compartment reserved for passengers.
It shall be capable of maintaining a minimum inside temperature of 16ºC when the outside temperature is -18ºC, the engine is idling and the ambient air is moving at a maximum speed of 5 km/h.
For the purposes of the second paragraph, the inside temperature shall be measured at a point located between 40 cm and 45 cm from the floor, at the centre of the bus or minibus.