What is AHUin construction?

An AHU is an indoor air-side unit, usually in a mechanical room, that moves and conditions air but relies on remote equipment (a chiller, boiler, or condensing unit) for its cooling and heating source, and it is sized in cfm. An RTU is a packaged rooftop unit with its own compressors and heat source built in, sized in tons. RTUs suit low-rise buildings with available roof area; AHUs serve larger or taller buildings with central plants.

Cfm is cubic feet per minute, the volume of air the unit moves. It is the single best proxy for an AHU's physical size and cost: higher cfm means larger fans and motors, a bigger casing, deeper coils, and heavier rigging. The schedule also lists external static pressure and motor horsepower, which push price within a cfm class, so two units with the same airflow are not automatically the same money.

A built-up AHU is assembled in the field inside a mechanical room from individual components (fans, coil sections, filter racks, casing panels) rather than arriving as a factory package. They appear on large hospital, laboratory, and industrial projects where airflow or space constraints exceed packaged offerings. For estimating, a built-up unit shifts cost from equipment to field labor and stretches the schedule, so it cannot be priced from a packaged unit's cost per cfm.