Dunkirk 550002635 Conversion Kit Lp/Natural Gas Q90-50 S2/S4 . Since the late 1920's, Dunkirk has delivered innovative, efficient and dependable home heating systems to professionals, building owners and homeowners. This is the best way to deliver heating equipment that lasts and reduces home heating costs. These Replacement Parts are designed to perform the way they were originally intended to, or upgrade your Dunkirk products for better performance. All These Parts are specifically designed for Dunkirk Boilers. Part of the Q90 Series.