Published Friday, March 29, 2013 at 1:58 am / Updated at 3:46 am

STORM LAKE, Iowa — High levels of carbon monoxide have been found at a restaurant that had been evacuated in northwest Iowa.

The Storm Lake Fire Department, police and Alliant Energy responded to a Burger King outlet Tuesday night after an odor related to natural gas was reported. The restaurant had been evacuated.

Authorities said no natural gas was detected, but carbon monoxide was. Firefighters determined a faulty rooftop heating unit caused the problem.

Problem: Faulty rooftop heating unit.