Upper Darby police say 22-year-old Anna Mae Croumbley was found dead in the basement bedroom of her family's home around 4 a.m. Sunday.
Officials say a carbon monoxide alarm went off in the adjoining twin home, alerting neighbors. Firefighters who arrived at the scene evacuated both homes and found Croumbley unresponsive.
Police Superintendent Michael Chitwood says investigators found a clogged chimney flue and forced the deadly gas back into the basement. He said Croumbley's father had turned on the heat about an hour earlier for the first time this year.