Heat tape plugged into an extension cord was determined to be the cause of a house fire on the 500 block of North 48th Avenue West early Thursday.

The house was not occupied when Duluth firefighters arrived at 4:21 a.m., to find fire coming out windows on two sides of the main floor, a Duluth Fire Department news release said.

Water lines knocked down the flames and firefighters checked for hidden fires. The Fire Marshal determined the cause on scene, and damages were estimated at $50,000.

A Lincoln Park fire crew brought the first two engines to the scene, confirming no one was living in the house. Twenty firefighters responded to the fire and no injuries were reported.