The fire department received a call at 1:16 a.m. about the fire in the 700 block of Sutter Avenue.
A total of three fire engines, one ladder truck, one rescue unit and the battalion chief were dispatched to the scene.
The fire had broken through a window to the garage so fire crews immediately started applying water on the fire through the broken window.
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The fire was brought under control at 1:43 a.m.
The fire investigator conducted a scene examination and deemed the fire accidental, caused by a portable heater that was too close to combustible material. It had been plugged in and running since 6 p.m. the previous evening, they said.
Damage is estimated at $50,000.
There no injuries to civilians or firefighters as a result of the fire.