IAPMO UMC MPE cheat sheet

The Uniform Mechanical Code governs installation, alteration, repair, relocation, replacement, and maintenance of mechanical systems; existing lawful installations need not be upgraded unless the code or the authority having jurisdiction (AHJ) requires it.

A permit is required before installing or altering mechanical work; ordinary repairs and replacements of components in kind generally do not require a permit, but the AHJ makes the final determination.

Construction documents must show the size, location, and routing of ducts, piping, and equipment, plus the required clearances, and must be prepared by a licensed design professional where the code or local law demands.

The AHJ is empowered to interpret code provisions, approve alternate materials and methods equivalent in quality and safety, and require tests to prove compliance.

Inspections must be requested at defined stages: rough-in before concealment, and final inspection after the system is complete and operable; concealed work cannot be covered before approval.

Approved materials and appliances must be listed and labeled by an approved agency where the code requires listing; field-modified listed appliances lose their listing unless the modification is approved.

Code editions are adopted by local ordinance; when the code text and the manufacturer's installation instructions conflict, the more restrictive requirement governs.

Unsafe or unlawful installations may be condemned, disconnected, or tagged out by the AHJ, and the building official may order the work corrected before service is restored.

Ducts must be sized by an approved method such as equal friction, static regain, or velocity reduction; supply, return, and exhaust air quantities must be shown on the plans.

Minimum duct thickness and reinforcement depend on the longest side of the duct and the operating static pressure; higher pressure classes require heavier gauge or closer reinforcement spacing.

Ducts must be supported at intervals set by the code, typically not exceeding 12 feet for horizontal rectangular ducts, with supports designed for the weight of the duct plus insulation.

Joints, seams, and connections must be sealed to the pressure class of the system; Sealant must be applied to transverse joints on higher-pressure systems and to longitudinal seams as specified.

Return air cannot be drawn from a bathroom, toilet room, kitchen, closet, garage, or furnace room, and return-air openings in bedrooms must not be located where a door can block the required return path.

Duct penetrations of fire-rated assemblies require listed fire dampers, and penetrations of smoke barriers require smoke dampers, installed with approved access for inspection and maintenance.

Friction loss in flexible duct is roughly two to three times that of rigid galvanized duct of the same diameter; flexible duct must be fully extended and limited in length and number of bends.

Air distribution design must maintain the required outdoor air ventilation rate and prevent short-circuiting between supply and return; transfer grilles or undercut doors provide the return path for closed rooms.

Category I appliances operate at non-positive vent pressure and produce flue-gas temperatures high enough to avoid condensation; Category IV appliances operate at positive vent pressure and condense, requiring corrosion-resistant venting.

Indoor combustion air from an unconfined space requires a volume of at least 50 cubic feet per 1,000 Btu/h of total input; below that threshold the space is confined and dedicated air openings are required.

Outdoor combustion air through vertical ducts requires 1 square inch of free area per 4,000 Btu/h; through horizontal ducts, 1 square inch per 2,000 Btu/h.

Combustion air openings require two permanent openings, one within 12 inches of the top and one within 12 inches of the bottom of the enclosure, each sized for the full required free area.

A single permanent opening may be used for direct-vent or listed appliances when permitted, sized at 1 square inch per 3,000 Btu/h of total input.

Vent connectors must slope upward toward the chimney at not less than 1/4 inch per foot, be as short and direct as practicable, and be supported and joined with screws or approved fasteners.

Type B vent has a listed double wall and requires a specified clearance from combustibles, commonly 1 inch; single-wall connectors require greater clearance, commonly 6 inches.

Masonry chimneys must be lined and sized for the appliance; flue sizing that is oversized causes condensation and poor draft, and a flue must not serve both a gas appliance and a solid-fuel appliance unless listed for the combination.

Appliances must be installed per the manufacturer's listing and instructions, and the required clearances to combustibles must be maintained unless a listed clearance-reduction means is used.

Appliances installed in garages must be protected from vehicle impact, and ignition sources must be elevated so burners and pilots are at least 18 inches above the floor.

Appliances in attics and crawl spaces require an unobstructed passageway and a level service platform large enough to service the equipment, with lighting and a receptacle where required.

Condensate from cooling coils and condensing appliances must drain by gravity or an approved pump to an approved receptor, with a trap where required and protection against freezing.

Refrigerant-containing coils and air handlers require access for service, and the appliance must be accessible without removing permanent construction.

Vibration isolation, flexible connectors, and seismic restraints are required where the code or local amendments mandate them, and equipment must be secured against displacement.

Clearance to combustibles is measured from the appliance casing or listed spacing, and insulation with a foil or other combustible facing counts as a combustible surface.

Appliances must be connected to the vent and to the fuel supply with approved connectors, and shutoff valves must be accessible and located within the same room or adjacent to the appliance.

Refrigerants are classified by safety group (A1, A2L, A3, B1, etc.) based on toxicity and flammability; the refrigerant quantity allowed in an occupied space depends on the classification and the space volume.

The refrigerant concentration limit (RCL) is expressed in pounds per 1,000 cubic feet or in parts per million; the quantity in a space must not exceed the RCL for the refrigerant used.

A2L refrigerants are mildly flammable and require ignition-source controls, leak detection, and ventilation in occupied spaces above the allowable charge threshold.

Refrigerant piping must be supported at intervals set by the code, protected from physical damage, and isolated from vibration; piping passing through occupied spaces must be brazed and leak-tested.

Pressure testing of refrigerant piping is performed with dry nitrogen, never with oxygen or air, to the test pressure specified by the manufacturer or code, followed by evacuation to the required micron level.

Machine rooms for large refrigeration systems require ventilation, refrigerant detection, and emergency discharge provisions, and must not be used for storage.

Refrigerant piping must be insulated where it passes through conditioned spaces or where condensation can occur, and the vapor line requires insulation to control capacity loss.

Refrigeration systems must have a means of pressure relief where required by the code, and relief piping must discharge to a safe location outside the building.

Hydronic piping must be supported at intervals based on pipe size and material, with supports designed for the weight of the pipe, insulation, and fluid.

Expansion tanks and air-elimination devices are required on closed hydronic systems to accommodate thermal expansion and remove entrained air.

Relief valves are required on boilers and on closed hydronic systems, and the relief valve discharge must terminate at a safe point of disposal.

Piping must be arranged to allow drainage, venting, and isolation of equipment, and valves must be accessible for operation and service.

Backflow protection is required where a hydronic system connects to a potable water supply, and make-up water connections must be protected against cross-connection.

Insulation of hydronic piping is required where the code or energy provisions mandate it, and insulation must be rated for the operating temperature and protected from moisture.

Glycol solutions require a higher percentage of expansion volume and derate system capacity; the freeze protection concentration must be maintained and verified.

Piping must be protected from freezing and from physical damage, and piping in concealed spaces must be installed so that it can be inspected before concealment.

Local exhaust is required at sources of contaminants such as cooking, soldering, spraying, and laboratory work, and the exhaust must discharge outdoors away from air intakes and operable openings.

Domestic kitchen exhaust hoods must be ducted outdoors; recirculating hoods are permitted only where the code allows and the hood is listed for that use.

Commercial kitchen hoods over cooking appliances require a Type I hood for grease-laden vapors and a Type II hood for other cooking vapors, with listed fire suppression for Type I.

Bathroom and toilet room exhaust must be provided at the rate required by the code, and exhaust must not be recirculated into other spaces.

Exhaust ducts for clothes dryers must be smooth, of the required diameter, limited in developed length, and must terminate outdoors with a backdraft damper.

Outdoor air intakes must be located away from exhaust outlets, plumbing vents, loading docks, and other contamination sources, with the minimum separation distances set by the code.

Balanced ventilation is required for tight construction where the code mandates mechanical outdoor air; exhaust-only systems can depressurize the building and cause backdrafting of combustion appliances.

Air filters must be accessible for replacement, and the filter rack must be sized so that filters fit without bypass; filter pressure drop must be considered in fan selection.

Fuel-gas piping must be sized by an approved method such as the longest-length or branch-length method, accounting for the total connected load, the allowable pressure drop, and the gas specific gravity.

Gas piping must be supported at intervals set by the code, commonly not exceeding 6 feet for Schedule 40 steel pipe, and must be protected from physical damage and corrosion.

A shutoff valve is required ahead of each appliance, and a union or approved connector must be provided for removal of the appliance.

A sediment trap is required at each appliance connection, installed downstream of the shutoff valve and arranged so that the trap can be cleaned.

Gas piping must be tested with air or inert gas at the pressure and for the duration specified by the code; the test pressure must not exceed the pressure rating of any component.

Gas piping must not be installed in or through ducts, plenums, or chimneys, and concealed piping must be protected against corrosion and located so it can be serviced.

Flexible appliance connectors must be listed, of the correct length, and must not pass through walls, floors, or ceilings.

LP-gas piping and appliances have different sizing and clearance requirements than natural gas, and LP-gas containers and regulators must be located per the code and the listing.

Solar thermal systems must be protected against overheating and freezing, with expansion control, relief devices, and a means to dissipate stagnation energy.

Solar collectors must be supported and anchored for wind and snow loads, and roof penetrations must be flashed and sealed against water intrusion.

Solar thermal systems must be separated from potable water by an approved heat exchanger or backflow protection where freeze protection or antifreeze is used.

Solid-fuel appliances require a chimney or vent listed for solid fuel, with the required clearance to combustibles and a barometric damper only where the listing permits.

Solid-fuel appliances need a source of combustion air and a means to limit spillage; a carbon monoxide alarm is required in the space where the appliance is installed.

Wood stove clearances to combustibles are set by the listing and cannot be reduced except by a listed clearance-reduction assembly installed per its listing.

Pellet and other automatically fed appliances require a listed vent and must be installed per the manufacturer's instructions, including the required vent height and termination.

Specialty systems such as direct-fired heaters, infrared heaters, and pool heaters must be listed for the application and installed with the clearances and venting specified in their listings.

Plan review verifies that the submitted drawings show code-compliant sizing, clearances, venting, combustion air, and structural support before a permit is issued.

Rough-in inspection must occur before ducts or piping are concealed, and the inspector verifies support, clearances, materials, and routing.

Final inspection verifies that the system operates correctly, that controls and safety devices function, and that the installation matches the approved plans.

Duct leakage testing may be required for systems above a specified pressure class or for systems serving certain occupancies, and the test results must be documented.

Gas piping must be pressure-tested and the test witnessed or documented as required by the AHJ before the system is placed in service.

Combustion appliance venting is verified by checking draft, spillage at the draft hood, and the presence of carbon monoxide alarms where required.

Refrigerant systems are verified by leak testing, evacuation to the required vacuum, and confirmation that the charge matches the manufacturer's specification.

Approved plans and permits must be kept on the job site and made available to the inspector, and any field change from the approved plans requires revised approval.