Huntsville Fire and Rescue are investigating how an early morning house fire started. Fire crews said the call went out just after 6:15 Wednesday morning about a house fire on the 45-hundred block of Sparkman Drive. Someone driving by the home saw smoke and called 911. When firefighters arrived, they said heavy smoke filled the house. They believe the fire started in the bedroom, but officials say the entire house sustained smoke damage. Firefighters said no one was home at the time of the fire and they have not been able to locate the homeowners. A portion of Brookline Drive and Sparkman was closed off by Huntsville Police while firefighters worked to put out hot spots. Crews are working to determine how the fire started.