IAPMO UMC MI cheat sheet

The UMC governs the design, installation, alteration, repair, relocation, replacement, and maintenance of heating, ventilating, cooling, refrigeration, and evaporative systems, including associated piping, ducts, vents, and controls.

Chapter 3 covers general regulations: access, clearances, equipment identification, and the requirement that appliances be listed and installed per their listing and the manufacturer's instructions.

Combustion air requirements are performance-based: appliances must receive adequate air for combustion, dilution, and ventilation, and the code permits either the prescriptive indoor-air methods or engineered (proven) designs.

Vent sizing and termination rules tie appliance input rating, vent height, connector rise, and category (I through IV) to the applicable venting tables or listed vent systems.

Duct construction is classified by static pressure and velocity into pressure classes; ducts must be sealed to the required leakage class and supported at code-specified intervals.

Refrigerant classification follows safety group designations (A1, A2L, A3, B1, etc.); higher-flammability and higher-toxicity refrigerants carry stricter occupancy, charge-limit, and ventilation restrictions.

Condensate drains require a trap where required, slope to a point of disposal, and protection against freezing; secondary drain or pan protection is required where overflow could cause damage.

Appliances in attics, crawl spaces, and closets must have a service access opening sized to the equipment, and access must not pass through another tenant's space.

Sensible and latent load calculations (Manual J or equivalent accepted method) establish equipment sizing; oversized equipment causes short cycling, poor dehumidification, and comfort complaints.

Duct design uses equal-friction or static-regain methods; total external static pressure must not exceed the air handler's rated capability, and friction loss plus component drops must be totaled.

Refrigerant line sizing depends on capacity, equivalent length, and oil return; suction lines must maintain adequate velocity for oil return while liquid lines limit pressure drop.

Combustion appliance venting: Category I appliances use natural draft with a listed vent; Category IV (condensing) appliances require listed plastic venting and slope back to the appliance for condensate.

A gas piping system is sized by the longest length method or branch length method using the tables, accounting for specific gravity and pressure drop allowances.

Flexible duct runs should be as short and straight as practical; compression and sharp bends reduce delivered airflow and effective capacity.

Outdoor units need clearances for airflow and service per the listing; recirculation of discharge air reduces capacity and can trip high-pressure controls.

Hydronic systems require air elimination, expansion control, and circulation designed to the pump curve; incorrect pump selection causes noise or insufficient heat delivery.

A pressure test of refrigerant piping is performed with dry nitrogen (or per code) before evacuation; the system is then evacuated to a specified micron level and held to verify no leaks.

Gas piping is tested with air or inert gas at the code-specified pressure for the specified duration, with the test medium and gauge visible to the inspector.

Duct leakage testing is required where the code mandates it; the measured leakage must not exceed the leakage class for the duct's pressure class and seal level.

Combustion testing verifies steady-state efficiency, carbon monoxide in flue and ambient air, and draft; CO above safe thresholds indicates incomplete combustion or venting problems.

Final mechanical inspection confirms equipment listing, clearances, access, support spacing, seismic restraint where required, labeling, and that permits match installed work.

Preventive maintenance includes filter replacement, coil cleaning, belt and bearing inspection, refrigerant charge verification by superheat/subcooling, and combustion analysis.

Superheat and subcooling measurements confirm charge: high superheat with low subcooling suggests undercharge; high subcooling with high head pressure suggests overcharge or restricted airflow.

Records of inspections, test results, and maintenance should be retained and made available to the authority having jurisdiction on request.

A mechanical permit is required before installing, altering, or replacing regulated mechanical equipment; ordinary repairs and minor maintenance are typically exempt but must still comply with the code.

Permit applications must include plans, specifications, and equipment data sufficient to show code compliance; the AHJ may require engineered drawings for complex systems.

Work must not be concealed until inspected and approved; a request for inspection is filed when the installation reaches the stage the code designates for that inspection.

A certificate of occupancy or final approval is issued only after final inspection confirms the work complies with the approved plans and the code.

The AHJ has authority to stop work, revoke permits, and order correction of unsafe or noncompliant installations; stop-work orders remain until the defect is corrected.

Approved plans and permits must be kept on the job site and made available to the inspector; deviations from approved plans require a revised permit.

Appeals of AHJ decisions go to the board of appeals established by the jurisdiction, within the time and manner the local ordinance specifies.

Fees, permit expiration, and renewal rules are set locally; work must generally commence within the code-specified period and permits lapse if work is abandoned.

Enforcement begins with plan review: reviewers check equipment listings, clearances, combustion air, venting, duct class, and refrigerant safety group against code provisions.

Inspectors verify that the installed equipment matches the approved submittal; substituting an unlisted or differently rated unit is a code violation.

Unsafe conditions such as blocked combustion air, disconnected vents, or refrigerant leaks into occupied space may be ordered corrected immediately and equipment shut off.

Notice of violation should identify the code section, the specific defect, the required correction, and a reinspection date.

Reinspection fees and progressive enforcement (warning, citation, stop-work, permit revocation) are commonly authorized by local ordinance.

Inspectors document findings with photographs, measurements, and test results; the record supports any subsequent enforcement action or appeal.

Contractors must be licensed and, where required, bonded and insured; unlicensed contracting is a separate violation enforceable independent of the mechanical code.

AHJ interpretations of code provisions are binding for that jurisdiction until overturned on appeal or amended by the adopting ordinance.

Equipment located in a garage must be protected from physical damage and, where required, elevated so ignition sources are above the floor to reduce vapor ignition risk.

Appliances installed in plenums must be listed for plenum installation and have limited combustible and smoke-developed ratings.

Rooftop units require a structural curb, flashing, and clearances that maintain roof drainage and service access.

Equipment in bedrooms or sleeping areas is restricted; fuel-burning appliances generally cannot be installed in sleeping rooms unless direct-vent and specifically permitted.

Access to equipment for inspection and service must be provided without removing permanent construction or crossing through unrelated spaces.

Refrigerant-containing equipment in high-probability systems must comply with charge limits and ventilation requirements for the occupied space served.

Supply and return air must be balanced; a return path of adequate free area is required whenever doors or partitions can block airflow.

Dampers, turning vanes, and takeoffs must be installed to minimize turbulence and pressure loss at the fitting.

Duct insulation must be continuous at supports and joints; vapor retarders belong on the warm side to prevent condensation.

Return air from bathrooms, kitchens, and garages is prohibited; these spaces require dedicated exhaust.

Exhaust systems for commercial cooking require hoods listed to the application, with make-up air and grease duct construction per code.

Refrigerant leak detection is required in some occupancies and for certain refrigerant groups; detection systems must alarm and, where required, initiate ventilation.

Airflow verification uses a duct traverse or flow hood; measured airflow is compared to design and adjusted with dampers or fan speed.

Electrical connections, disconnects, and overcurrent protection are inspected alongside mechanical equipment because they affect safe operation.

Condensate drain testing confirms slope, trap function, and no overflow; a secondary drain or float switch protects against water damage.

The permit holder is responsible for the work's compliance and for requesting inspections at required stages.

The AHJ may require a licensed design professional's seal for systems above code-specified thresholds or complexity.

Changes in use or occupancy may trigger new mechanical requirements even without new construction.

Inspection results and approved plans are public records under local law; contractors may obtain copies for their files.

Confirm clearances to combustibles around appliances and vent connectors; reduced clearance requires a listed clearance-reduction method.

Verify combustion air openings are unobstructed and sized to the method used (two-permanent-opening or one-opening rules).

Check that vent terminations meet height, distance from windows and intakes, and that vents are supported and properly joined.

Confirm refrigerant piping is supported, insulated, and protected at penetrations, and that line sets are not kinked or over-bent.

Verify equipment labels, ratings, and installation instructions are available on site for the inspector.