For a fire extinguisher, I would recommend at a minimum 5 pound B,C. Inspect the extinguisher regularly(nozzle clear, unit still has pressure, etc.). While you have it out read the directions again as a refresher. Also invert the unit and shake it vigourisly to ensure the powder has not caked and become a solid mass. I once responded to a fire that started in the man's car under the carport. His extinguisher powder had caked and the unit would not discharge when he tried to put out what was initially a small fire. We saved half the house after it spread from the car.