ICC M2 key terms

Acceptable to the code official because the material, device, or method conforms to a recognized standard or is listed by an approved agency. When the code says something must be approved, documentation or a listing mark is the usual proof.

Equipment or material included in a published list by an organization concerned with product evaluation, which maintains periodic inspection of production. Listing means the product was tested and continues to be checked against a standard.

Bearing a label, symbol, or other identifying mark of an approved agency showing compliance with a standard. The label is the visible evidence on the equipment that it is listed for the intended use.

The officer or authority charged with enforcing the mechanical code, or an authorized representative. This person reviews plans, issues permits, conducts inspections, and has authority to approve or reject installations and require corrections.

Written authorization from the code official to install, alter, or replace regulated equipment. Work generally may not begin until the permit is issued, and the permit identifies the scope of work that was approved.

The on-site examination by the code official of work for which a permit was issued, to confirm it complies with the code before it is covered or placed in service. Required inspections typically occur at rough-in and final stages.

The minimum distance that must be maintained between equipment or venting and combustible material, or the open space required for service access. Clearances are measured to the nearest combustible surface and may be reduced only by listed methods.

An enclosed space that is part of the air distribution system and is used to convey or distribute conditioned air. Because air passes through it, materials exposed inside a plenum have stricter flame and smoke limits than ordinary room surfaces.

A closed conduit made of metal, fiberglass, flexible material, or other approved material used to convey air between equipment and occupied spaces. Ducts must be supported, sealed, and constructed of materials suited to the application.

Air drawn from conditioned spaces back to the heating, cooling, or ventilating equipment for recirculation. Return openings and pathways must be sized, located, and protected so air is not drawn from prohibited sources such as garages.

A factory-made duct, usually with a wire helix and a flexible jacket, that can bend around obstructions. It must be listed, limited in length and sag, and supported at intervals so it does not restrict airflow.

The air supplied to a fuel-burning appliance for mixing with fuel and supporting burning. It must be provided from indoors, outdoors, or a combination, in quantities calculated from the appliance input rating and the method used.

For combustion air purposes, a room or space small enough relative to appliance input that it cannot reliably supply enough air from normal infiltration. Such spaces require specifically designed air openings or ducts.

A permanent opening or duct that brings outside air into a space containing fuel-burning appliances. Sizing depends on whether the opening is direct or through a duct and on the total input of the appliances served.

A device on a draft-hood-equipped appliance that limits stack effect by drawing dilution air, keeping the flue pressure near neutral. It helps stabilize venting and prevents excessive draft from pulling heat or flame from the burner.

The passageway or conduit that carries flue gases from an appliance to the outdoors. Vents must be sized, pitched, supported, and terminated according to the appliance category and the venting method selected.

The internal passage within a vent or chimney through which combustion products travel. Flue sizing is matched to appliance input and appliance category so gases rise steadily and exit outdoors.

A listed factory-built vent with a double wall and air space, intended for listed gas appliances producing flue gases within specified temperature limits. It requires clearance to combustibles per its listing.

A vertical masonry or factory-built structure enclosing one or more flues that carry combustion products above a roof. Chimneys serving appliances must be lined, sized, and maintained to safely vent gases.

A gas appliance that operates with negative vent pressure and flue gas temperatures low enough to avoid condensation damage in the vent. These appliances are typically vented with Type B vent or an approved chimney.

A hinged draft-control device installed in a vent connector or breeching that admits room air to regulate draft. It is used only where the appliance listing and vent design permit it, and must not be installed on some appliance types.

The fluid used in a refrigeration cycle that absorbs heat while evaporating and releases it while condensing. Its classification and safety group determine how the system may be installed, occupied, and serviced.

The assembled equipment and piping that produce a cooling effect, including compressor, condenser, evaporator, and controls. Installation must address refrigerant quantity, ventilation, access, and protection of the space served.

A space dedicated to mechanical equipment such as boilers, furnaces, or refrigeration machinery. Access, clearances, combustion air, and ventilation requirements are applied based on what equipment the room contains.

A heating or cooling system that uses water or another liquid as the heat-transfer medium, distributed through piping to terminal units. Design must account for expansion, pressure relief, and temperature limits of materials.

A tank connected to a hydronic system that absorbs the volume change of heated water and helps maintain pressure. It may be closed with a diaphragm or open, and must be located and sized for the system it serves.

A pressure-actuated device that opens automatically to discharge fluid when system pressure reaches its set point, protecting equipment from overpressure. It must be sized for the equipment and piped to a safe discharge point.

A closed vessel in which water or another liquid is heated by combustion or another heat source. Installation requirements cover clearances, relief devices, combustion air, venting, and the temperature and pressure limits marked on the appliance.

A warm-air heating appliance that heats air for distribution through ducts. Its installation involves combustion air, venting, clearances, and proper connection to a duct system sized for the appliance airflow.

The piping, tubing, and fittings that deliver fuel gas from the point of delivery to appliances. Materials, sizing, support, protection, and testing must follow the fuel gas provisions, and joints must be of approved type.

A listed flexible or semirigid connector used to join an appliance to the house piping. It must be installed within its listed length, protected from damage, and not concealed in a way that hides defects.

A valve installed in the fuel gas piping or at a fixture supply so the gas can be isolated for service or emergency. It must be accessible, of an approved type, and clearly identified for the equipment it controls.

A removable or hinged cover that allows inspection and service of concealed equipment, valves, or controls without destructive demolition. Appliances and components requiring service must remain accessible as required by the code.

A pipe or channel that carries liquid water removed from combustion gases or from cooling coils to an approved disposal point. It must be trapped, pitched, and protected from freezing where required.

An appliance that takes combustion air from outdoors and discharges flue gases outdoors through a dedicated vent, with no dependence on indoor air. Its vent terminal location and clearances are specified by the listing and code.

The duct section that carries air from occupied spaces back to the air handler. It must be sealed and routed so it does not draw air from garages, appliance rooms, or other prohibited locations.