The fire, located in the 100 block of Tucker Avenue near John McLaren Park, was reported at 12:45 a.m.
"Immediately they encountered problems with forcible entry and noticed that obviously this is a highly secured building, which is somewhat unusual for this type of residence. It immediately became apparent as they were advancing a hose line in the inside that this was a marijuana grow operation," said Asst. San Francisco Fire Department Assistant Chief Matthew McNaughton.
Investigators said the home was empty at the time and they found five rooms with marijuana growing equipment in them. The house was bypassing the PG&E meter and investigators believe the fire may have been started by an electrical issue.