Michigan Compiled Laws, Chapter 339. Occupational Code § 339.5915

(a) Boilers under federal control.

(b) Boilers used in the power plants of self-propelled vehicles designed primarily for the transportation of individuals or property on a highway, except vehicles used exclusively on stationary rails or tracks.

(c) Boilers used solely for agricultural purposes.

(d) Steam or vapor boilers that carry a pressure of not more than 15 p.s.i.g. and are located in a private residence or in an apartment building with a capacity of fewer than 6 families.

(e) Hot water boilers operated at a pressure that does not exceed 160 p.s.i.g. or a temperature that does not exceed 250 degrees Fahrenheit and are located in a private residence or in an apartment building with a capacity of fewer than 6 families.

(f) Miniature steam or marine engines used as a hobby.

(g) Boilers used on farms for mint processing purposes.

(h) Subject to section 919,  1 miniature hobby locomotives that operate on narrow gauge tracks that are less than 24 inches in width.