A ceiling fan or a vent fan?
Many ceiling vents are pre-wired for vent fans and if not, usually there is a light nearby one can typically tap into for power. Vent fans are 12v. Many have what they call 'ceiling fan mode' and can be run in reverse with the vent lid closed.
Most ceiling fans are 120v but there are a few RV models out there (if you can find one) that are 12v as well.
2016 Flagstaff 8529IKBS Diamond Package 5th Wheel-Goodyear Endurance Tires
2017 Ford F-Series SCREW 4x4 - Factory Puck B&W Companion
TST Tire Monitor w/Repeater - Sinemate 3500w Gen.
Days Camped: '17=30 ☼ '18=51 ☼ '19=58 ☼ '20=88