Mich. Admin. Code R. 460.859
Rule 9. Heaters for preventing freezing in wellhead connections shall be installed or reinstalled for service at the beginning of each winter, only after wellhead connections are checked for leakage, and after any leakages have been repaired and stopped. The products of combustion, or the burned fumes from gas or any other fuel, shall not be used in such heaters or in any other way to apply heat directly to wellheads or to thaw out connections. The points of air mixture for any flame at any wellhead heater shall be located at least 10 feet from the wellhead, and any burned exhaust gases shall be discharged from flue or chimney at least 8 feet from wellhead or wellhead connections and at least 4 feet higher than the top of wellhead connections. All heaters installed at or near wellheads shall be inspected at least once daily while in operation.
Mich. Admin. Code R. 460.859