What was found
DURING A HOLDING PATTERN, THE F/A REQUESTED MORE HEAT FOR A COLD CABIN. AFTER THE COCKPIT CREW ADJUSTED THE TEMPERATURE UP, THE F/A REPORTED SMOKE AND HAZE FILLING CABIN. COCKPIT CREW DONNED O2 MASKS AND ADJUSTED THE TEMP BACK DOWN AND HAZE DISSIPATED. MAINTENANCE CLEANED THE APU INLET AS A PRECAUTION AND COMPLETED A DUCT BURNOUT. NO FURTHER SMOKE, HAZE, ODOR NOTED.