The air that comes from the tailboom (slots or thruster) is the same temperature at the air around the helicopter. The air that operates the NOTAR system is drawn in from above (large opening behind main rotor) via a fan driven by the output shaft of the transmission. The air is accelerated down the tailboom (not a compressor as the pressure in the tailboom is not much of an increase) and some exits the slots, the rest exits the thruster- at the same temp (differences as in any increased velocity like you home cooling fans) as it entered. I don't understand how after 20 years people still think engine exhaust is used in teh NOTAR system.