The fire was reported at 10 a.m. Monday in the 200 block of Edjil Drive.
Firefighters quickly got the fire under control.
One man was taken to Christiana Hospital to be treated for smoke inhalation.
Investigators say a space heater in the bedroom was placed too close to combustible materials.
There were no smoke alarms in the house.
Fire officials say two adults and five children are now out of their home.