A faulty HVAC unit sparked a fire in a Bay City apartment early Monday, displacing a grandmother and her two grandchildren. The blaze began around 6:30 a.m. in the 5000 block of Avenue F after the resident turned on the heat and heard popping sounds before spotting smoke. Firefighters quickly contained the flames to the bathroom within 15 minutes, though smoke damage spread throughout the unit. No injuries were reported, and damages were estimated at $20,000. The Red Cross is assisting the displaced family.