NATE Air Distribution Installation key terms

A required procedure for shutting off and isolating energy sources, such as electrical disconnects or gas valves, and applying locks and tags so equipment cannot be re-energized while someone works on it.

Wearable safety gear such as safety glasses, gloves, hard hats, hearing protection, and respirators that protects the installer from jobsite hazards including sharp metal edges, dust, and noise.

A permit-controlled process for entering spaces with limited access or poor ventilation, such as plenums, crawlspaces, or mechanical rooms, requiring atmospheric testing and an attendant before entry.

Systems and practices, including guardrails, personal fall arrest harnesses, and ladder safety rules, used to prevent injury when working at heights such as rooftops or elevated platforms.

Correct selection, setup angle, inspection, and three-point contact practices for ladders, plus rules limiting reach and requiring secure footing before climbing to install or service ductwork.

An ACCA residential duct design method that sizes ducts using room-by-room airflow, available static pressure, and a calculated equivalent-length friction rate so each terminal receives its design airflow.

An ACCA method for calculating residential heating and cooling loads room by room from construction details, orientation, and climate data; its results drive equipment and airflow selection.

The total effective resistance of a duct run expressed in feet of straight duct, adding fitting losses from elbows, tees, and transitions to actual measured length.

The pressure drop per 100 feet of duct run that a design uses to size ductwork, derived from available static pressure divided by total equivalent length.

The portion of a blower's total external static pressure left for the supply and return duct system after subtracting pressure drops of coils, filters, grilles, and other components.

The resistance to airflow measured across the air handler, including the duct system and accessories, usually expressed in inches of water column and compared with blower rating tables.

The pressure component associated with air speed in a duct, used with a pitot tube or flow grid to calculate velocity and airflow; it rises with the square of velocity.

The design cubic feet per minute a room requires, determined from its heating and cooling load and supply-to-room temperature difference, and used to size the branch run and terminal.

Pressure lost as air passes through an elbow, tee, takeoff, transition, or boot; it depends on fitting geometry and velocity and is added to straight-duct loss in design calculations.

The width-to-height ratio of a rectangular duct cross section; higher ratios increase friction and are generally limited to about 4:1 to keep pressure loss reasonable.

Ductwork formed from zinc-coated steel sheet, commonly used in commercial and residential systems; gauge selection depends on duct size and required static pressure.

The thickness designation of sheet metal duct, where lower numbers mean thicker metal; minimum gauges are set by standards based on duct dimensions and system pressure class.

Round duct made by winding a continuous metal strip into a spiral seam, offering low friction loss and high stiffness for exposed or long runs.

A factory-made duct with a wire helix and flexible jacket, used for short final connections; it must be installed taut, with limited sag and bends, to avoid excess pressure loss.

Rigid insulation board, often faced with foil or coated material, fabricated into duct sections; joints and seams must be sealed to control leakage and vapor migration.

A fitting that branches from a main trunk to feed a branch run, available in round, rectangular, and boot styles; its shape strongly affects pressure loss and airflow balance.

The maximum interval between supports for ductwork, set by code and manufacturer instructions, so the duct does not sag, rack, or separate at joints.

Bracing, cables, and anchors that keep ductwork and equipment from shifting during earthquakes, required in many jurisdictions and specified by seismic design categories.

A common rectangular duct seam with interlocking folded edges that is mechanically strong and, when sealed, resists air leakage along the longitudinal joint.

A channel-shaped metal strip slipped over the folded edges of adjoining rectangular duct sections to lock the transverse joint together before it is sealed.

A thick brushable or trowelable sealant applied to duct seams and joints to limit air leakage; it must be compatible with the duct material and rated for the pressure class.

A rating that groups duct systems by the static pressure they must contain, such as half-inch or one-inch water gauge, and sets required gauge, reinforcement, and seal level.

The box or duct section directly attached to the blower outlet that distributes conditioned air into the supply trunk and branch runs.

The duct section or chamber connected to the blower inlet that collects return air from the conditioned space and delivers it back to the air handler.

An adjustable blade inside a duct, branch, or terminal that throttles airflow so the delivered cubic feet per minute can be balanced to design values.

The process of measuring and adjusting dampers, registers, and fan settings so each zone and room receives its design airflow within acceptable tolerance.

A grille with an integral damper or deflector that covers a supply or return opening and directs or adjusts the air entering the room.

An air outlet with vanes or cones that spreads supply air in a designed pattern, promoting mixing and avoiding drafts in the occupied zone.

The horizontal or vertical distance air travels from an outlet before its velocity drops to a specified terminal value, used to judge draft risk and mixing.

A low-permeance layer that limits moisture diffusion through duct insulation or building assemblies, keeping the cold duct surface above the dew point.

A measurement of airflow made by averaging velocity readings across a duct cross section with a pitot tube or flow grid at a location with stable, uniform flow.

A pressurization test that measures air lost through duct seams and joints, often reported as leakage class or percent of design flow and compared with specification limits.

The documented record of measured airflows, pressures, fan speeds, and final damper positions produced after commissioning, used to verify the system meets design intent.

The organized process of verifying that installed duct and air distribution systems operate as designed, including functional testing, balancing, and documentation closeout.

A model code adopted in many jurisdictions that sets requirements for duct materials, installation, clearances, sealing, and ventilation, referenced by local permits and inspections.

Industry publications from the Sheet Metal and Air Conditioning Contractors' National Association that specify duct construction, pressure classes, reinforcement, and sealing requirements.

Product data, drawings, and calculations sent to the designer for approval before installation, confirming duct materials, gauges, sealants, and equipment meet the specification.

A drawing updated to show the ductwork and equipment as actually installed, including routing changes and field modifications, and used for closeout and future service.