The Panama City Fire Department responded to a call at 2:55 Saturday morning and arrived at West 12th Street just three minutes later.
Seventeen firefighters and seven fire trucks spent more than 20 minutes putting the flames out. Inside they found 90-year-old Horace O'Shield dead.
They say it appeared he tried to escape, but must have been overcome by the smoke and heat.
Investigators call it an accidental, slow-burning fire, and say a smoke detector could have alerted O'Shield much earlier, giving him a better chance of surviving.
The exact cause of the fire has not been released.