IAPMO UMC MPE key terms

The outward force per unit area exerted by air against the inside walls of a duct, measured in inches of water column. It drives duct sizing, fan selection, and leakage classification testing.

A rating of how much air a duct system loses through joints and seams under a specified test pressure, expressed as a percentage of design airflow or in cfm per unit area.

The straight-duct distance that would produce the same friction loss as a fitting, elbow, or transition. Adding equivalent lengths to measured runs gives total effective length for sizing.

A cavity, often formed by building framing or a dedicated chase, that carries return air back to the air handler. Its use as a plenum is restricted where combustible materials or gas appliances are present.

A listed device installed in a duct that closes automatically to resist the spread of smoke across a fire separation, often actuated by a smoke detector or fire alarm signal.

A listed closure installed where a duct penetrates a fire-rated assembly, designed to close on heat or fire exposure and protect the integrity of the rated separation.

The air supplied to a fuel-burning appliance for complete burning of gas or oil. It must be provided from indoors, outdoors, or a combination, in quantities set by the appliance input rating.

For combustion air purposes, a room or space whose volume is less than the threshold ratio to appliance input, requiring engineered openings or ducts to supply adequate air.

Air admitted to the draft hood or draft diverter of an appliance to stabilize draft and dilute flue gases. It is separate from the air needed for combustion itself.

A device on a natural-draft appliance that relieves excess draft and mixes dilution air with flue products, helping maintain steady venting and reducing spillage risk indoors.

The escape of flue gases from an appliance draft hood or burner area into the room instead of up the vent. It signals a venting or pressure problem and is a safety hazard.

A listed double-wall vent connector and chimney for venting listed gas appliances with draft hoods, using an inner liner and outer casing with an air space between them.

The pipe or duct that carries flue gases from the appliance flue collar to the chimney or vent. Its length, slope, and routing are limited to keep draft reliable.

A vertical passageway of masonry, metal, or listed components that conveys flue gases to the outdoors above the roofline, sized and installed to maintain adequate draft.

The minimum distance an appliance, vent, or duct must be kept from combustible material, as stated on the listing label or in the installation instructions, to prevent ignition from heat.

An appliance tested by an approved agency and bearing a label showing its certification. Listing governs installation, clearances, venting, and gas connections for that specific model.

The duct or fitting that connects an air-handling appliance to the duct system. It must be installed to limits on length and material and sealed against leakage.

A safety group assignment (such as A1 or B2) based on toxicity and flammability of a refrigerant. The classification controls allowable charge, occupancy limits, and piping requirements.

The tubing and fittings that carry refrigerant between components of a refrigeration system, subject to material, support, brazing, and pressure-testing requirements.

An enclosed space containing refrigeration equipment, with construction, ventilation, and access requirements tied to the refrigerant classification and total system charge.

The process of removing air and moisture from refrigerant piping with a vacuum pump before introducing refrigerant, followed by charging to the required weight or pressure.

Piping that circulates water or a water-based fluid for heating or cooling, including materials, fittings, expansion control, and provisions for air removal and drainage.

A vessel connected to a closed hydronic system that absorbs the increase in water volume as it heats, limiting pressure rise and protecting system components.

A device that removes entrained air from hydronic piping so it does not collect at high points or circulate through pumps and terminal units.

A listed capture device installed over cooking or contaminant-generating equipment to draw fumes, grease, and moisture away from the occupied space and into a duct system.

Outdoor air supplied to replace air exhausted by hoods, fans, or other exhaust systems, keeping the building near neutral pressure and supporting appliance draft and ventilation.

A duct of required construction used to convey grease-laden cooking vapors from a hood to the outdoors, with restrictions on materials, clearances, and access for cleaning.

Selecting pipe diameter so that pressure drop between the meter or regulator and each appliance stays within limits while delivering the required input to connected appliances.

A listed flexible or rigid connector that links gas piping to an appliance, subject to length, protection, and shutoff valve placement requirements.

A fitting arrangement installed in the gas line near an appliance to capture dirt and debris so it does not reach the burner controls or orifices.

A prescribed test of piping or equipment with air, inert gas, or other medium at a specified pressure and duration to prove joints are tight before placing the system in service.

The preconstruction examination of submitted drawings and specifications by the authority to confirm the design complies with code before permits are issued or work begins.

Written authorization from the authority having jurisdiction to install, alter, or repair regulated work, issued after application and any required plan review.

On-site verification by the authority that installed work matches approved plans and code, typically performed in stages such as rough-in and final before system use.

A system that collects solar energy to heat a fluid for domestic hot water or space heating, including collectors, piping, pumps, controls, and freeze protection provisions.

An appliance burning wood, pellets, or coal, installed with specific clearances, hearth protection, chimney requirements, and combustion air provisions different from gas appliances.

The provisions that establish what work the mechanical code covers, how terms are interpreted, and what approvals, permits, and referenced standards apply to installations.