Chuck Ardo, a spokesman for the mayor's office, said Tuesday morning that the space heater appeared to be located in the unit where the children died.
Fire crews arriving at the Monday night blaze found more than one row home engulfed in flames.
Ardo says a 48-year-old woman and four children ranging in age from 2 to 4 were killed. Their names were not immediately available.
Dauphin County Coroner Graham Hetrick is expected to speak at a news conference shortly.
