Firefighters responded at the corner of Mount Whitney and Valentine just before 11 p.m. Thursday night.
When they arrived they found the building fully engulfed in flames.
It took crews nearly an hour to contain the fire.
No one was hurt in the blaze, and no other buildings were threatened.
Firefighters say it appears a space heater may have tipped over, igniting items inside the building.
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Fresno fire officials are also investigating how a fire started at an auto-repair shop in West Central Fresno.
The fire happened at the Complete Auto Specialist on Shields and Cornelia.
Authorities believe someone doused flammable liquid on four cars sitting in the lot and lit them on fire.
The fire destroyed three of the cars. A fourth car suffered some damage.
Investigators say they believe the fire was a random act of vandalism.
