---
title: Air Handling Units
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description: >
When to use: Central station air handling units (AHUs) for commercial, institutional, and industrial buildings — both factory-built packaged units and field-erected built-up assemblies. Covers single-zone and multi-zone configurations, indoor and outdoor/weatherproof installations, constant-volume and variable-air-volume systems, and central-station units serving ductwork distribution. Applicable from small fan coil replacements through large mechanical room units.
− Not intended for: Unitary rooftop packaged units with integral refrigerant systems rated below 20 tons (see [[sync/rooftop-packaged-units]]); fan coil units and terminal units (see [[sync/fan-coil-units]]); dedicated outdoor air systems covered separately when paired with terminal sensible cooling; ductwork beyond the AHU connections ([[sync/hvac-ductwork]]); variable frequency drives for fan motors ([[sync/hvac-variable-frequency-drives]]); hydronic heating and cooling piping connected to coils ([[sync/hydronic-piping]]); testing, adjusting, and balancing after installation ([[sync/testing-adjusting-and-balancing]]); building automation system controls integration ([[sync/building-automation-system]]).
+ Not intended for: Unitary rooftop packaged units with integral refrigerant systems rated below 20 tons (see [[sync/packaged-rooftop-units]]); fan coil units and terminal units (see [[sync/fan-coil-units]]); dedicated outdoor air systems covered separately when paired with terminal sensible cooling; ductwork beyond the AHU connections ([[sync/hvac-ductwork]]); variable frequency drives for fan motors ([[sync/hvac-variable-frequency-drives]]); hydronic heating and cooling piping connected to coils ([[sync/hydronic-piping]]); testing, adjusting, and balancing after installation ([[sync/testing-adjusting-and-balancing]]); building automation system controls integration ([[sync/building-automation-system]]).
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### Filter section doors shall include a filter installation date tag holder for recording the date of each filter change.