Toledo police said the Ventura Drive home where a man and woman were found dead on Friday afternoon was heated to more than 100 degrees.
An autopsy is pending for the two siblings, who police said were 70 and 64 years old; voting records show the sister was the elder of the two.
Police were called to the home, 4868 Ventura, at 3:37 p.m. after another family member discovered the bodies in an upstairs room.
Police said today that the furnace malfunctioned. The home was so crowded with the resident's property that only one cold-air return vent was uncovered, causing the furnace to continue pushing heat into the home.