He was trained in architecture under an uncle, Volusin Bude, then in practice in Grand Rapids.
At the age of twenty-one began his career in Chicago. As draftsman for the late Francis Whitehouse, specialist in residential work, he assisted in Planning three distinguished homes of that period for his clients Colonel J. Mason Loomis, Barbara Armour, and General A. C. McClurg.
When in 1893 Mr. Whitehouse retired and moved to the east, Mr. Heun took over his practice, and acquired for himself a reputation in the field of domestic architecture. Noteworthy examples of his work were Melody Farm, Mrs. J. Ogden Armours estate near Lake Forest; the home of Frank Stout; residence of William McCormick Blair, Astor Street, and the Albert Loeb house on the south side. Mr. Heun also designed the Casino Club and the Art Club in the city.