Fire destroyed the McDonald's on Versailles Road in Frankfort on Wednesday night, Battalion Chief Dan Shouse said.
The fire was reported about 11 p.m., when employees noticed smoke coming from the heat and ventilation system's heat exchanger.
The employees left the restaurant, which had a 24-hour drive-through. No one was injured. The franchise is owned by Joe Graviss, who owns several McDonald's restaurants in Central Kentucky, Shouse said.
Shouse said investigators will focus on the heat exchanger to determine the cause of the blaze. Firefighters remained at the scene until about 4 a.m. Thursday.
"The extinguishment effort was hampered somewhat by the design of the building," Shouse said.
Metal awnings were pulled down to help firefighters battle the blaze, Shouse said. He said a frozen hydrant also caused a brief delay.