MIDLAND, MI — The Mechanical Inspectors Association of Michigan (MIAM) held its Fall Conference recently. Among the issues discussed were questions raised by inspectors on various Michigan residential and commercial codes.

The MIAM Residential Code Study seminar was chaired by Guy Mitchell, mechanical inspector for the city of Royal Oak, MI. He is co-chairman of the MIAM Education Committee. The MIAM Commercial Code Study seminar was chaired by Grayle Woodruff, mechanical inspector for the city of Norton Shores, MI, and current president of MIAM.

The questions discussed covered a variety of topics. The answers below were provided by MIAM. (Note: These answers are specific to the state of Michigan. Codes in other states may vary.)


  • Can bushings be used in residential gas piping systems?

    Yes, according to the Michigan Residential Code (MRC). The majority of inspector attendees at the meeting believed that bushings should not be used and would like to see a change in the code.

  • Is insulation required on bathroom exhaust ventilation ductwork?

    No, there is no regulation in the MRC or the Michigan Mechanical Code (MMC) that requires the use of insulation on bathroom exhaust ventilation ductwork. Attendees were split about 50/50 on whether this code should be changed.

  • Is combustion air required during furnace replacement in homes built before 1976?

    Yes, the MRC, MMC, and the International Fuel Gas Code (IFGC) all have sections that require the use of combustion air for the installation of fuel-burning appliances.

  • Do residential duct joints and seams need to be sealed?

    Yes, joints of duct systems shall be made substantially airtight by means of tapes, mastics, gasketing, or other approved closure systems. MIAM materials state, “According to HVAC industry studies, leakage of the duct joints can reduce the capacity of an HVAC system by as much as 25%. The HVAC system will not function as designed without sealing all joints and seams to eliminate air leakage. This could lead to very unsatisfied consumers and possible liability for inspectors.”

  • Does replacement with an 80% furnace require a listed chimney lining system when the existing chimney is not located on the exterior of the building?

    Yes, where an appliance is permanently disconnected from an existing chimney or vent, or where an appliance is connected to an existing chimney or vent during the process of a new installation, the chimney or vent shall comply with [appropriate sections] of the MRC.


  • What is the proper location of an air conditioning system smoke detector?

    Smoke detectors shall be installed in return air systems with a design capacity greater than 2,000 CFM in the return air duct or plenum upstream of any filters, exhaust air connections, outdoor air connections, or decontamination equipment and appliances.

  • The fire marshal requires a smoke detector in the main supply air duct. Do I have to install a smoke detector in the return duct, too?

    The fire marshal may require additional smoke detectors placed in another location of the air distribution system ductwork. The contractor must comply with all applicable codes from all authorities having jurisdiction.

  • Should the reset switch for the air conditioning system smoke detectors be located 48 inches above the floor to comply with ADA requirements?

    Clearances around appliances to elements of permanent construction, including other installed equipment and appliances, shall be sufficient to allow inspection, service, repair, or replacement without removing such elements of permanent construction or disabling the function of the required fire-resistance-rated assembly. The MMC and IFGC do not require that access to such equipment meet ADA compliance. Service personnel are able-bodied, and must climb on fixed or portable ladders to perform their regular duties.

  • Does the air conditioning system smoke detector have to be wired into the building’s fire alarm system?

    The smoke detectors shall be connected to a fire alarm system. The actuation of a smoke detector shall activate a visible and audible supervisory signal at a constantly attended location.

  • Is the material used by some fabric duct manufacturers approved for supply air ductwork?

    Nonmetallic ducts shall be constructed with Class 0 or Class 1 duct material in accordance with UL Standard 181. Fibrous duct construction shall conform to the Sheet Metal and Air Conditioning Contractors’ National Association (SMACNA) “Fibrous Glass Duct Construction Standards” and the North American Insulation Manufacturers Association (NAIMA) “Fibrous Glass Duct Construction Standards.” The maximum air temperature within nonmetallic ducts shall not exceed 250 degrees F.

    Publication date: 10/21/2002