Station 74 Delmar was dispatched for a chimney fire. The call was upgraded to a house fire with one subject trapped which added Station 81 Laurel, Station 5 Hebron and Station 16 Salisbury to the alarm. 74 Command arrived on-scene and found a 2 1/2 story, single family dwelling with nothing evident from the exterior. The homeowner reported a malfunctioning furnace with smoke filling the residence. No occupants were trapped or injured. Firefighters used Positive Pressure Ventilation to remove smoke from the house. Delmar Engine-Tanker 74-2, 74 Command, Paramedic B-74 and Laurel Engine 81-4 operated at the scene for 20 minutes. Engine-Tanker 1-1 and Engine-Tanker 5 were responding but placed in service prior to arrival.