The fire at the house on Swan Street near Tooley Street was reported about 4:10 p.m., and extinguished about 4:45 p.m., according to the San Diego Fire-Rescue Department.
No one was injured.
After the fire was out, a marijuana grow and a hash oil production operation were discovered, San Diego police Officer Frank Cali said.
Hash oil is produced using a flammable chemical, which police believed caused the explosion, Cali said.
Three people were detained, but it was unclear if any arrests were made, Cali said.
The Metro Arson Strike Team and narcotics detectives were investigating, he said.