Division 25 versus Division 23: equipment versus operable control

Conflict on projects is often mislabelled as “controls versus mechanical.” The useful split is: Division 23 owns the physical HVAC plant and its packaged safeties; Division 25 owns the integration of those plants into a building-level control system, including points that originate in other divisions. Packaged rooftop units with onboard controllers sit on the seam. If the spec is silent, the RTU ships with a proprietary bus, a thin BACnet object list, and no one responsible for the sequence the owner thought they bought.

How the investigation is actually run

Read the mechanical schedule and the controls specification on the same table, line by line, for one air handler before you generalise to the campus. Packaged rooftop logic is the usual trap: the sequence the owner wanted lives in a PDF, the logic that shipped lives in a controller with a thin object list, and Division 25 is asked to “integrate” a black box. Write which loops are unreachable.

Valves, dampers, VFDs and meters each need a furnished-by and a controlled-by. Smoke control needs a sentence that 25 will not casually override a life-safety sequence. When a dispute arrives, ask for the drawing that shows the signal and the paragraph that names the owner. If both are missing, the specification is the defect. Do not mediate personalities until the paper is honest.

The note ends when the seam is bid-able: package versus building controller, setpoint path, occupancy path, and the test that proves it. That is coordination, not a preference for one mechanical brand.

Division 25 documentation should state which loops live in the package, which live in the building controller, and how setpoints and occupancy arrive. Sequences that live only in Division 23 language (“provide controls as required”) are not executable. Turn them into architecture with from sequence to control architecture.

Typical overlaps

• Valves and dampers: furnished by 23, actuated and proven by 25 — unless the package includes both, which must be written.
• VFDs: electrical connection in 26, control word in 25, mechanical process in 23.
• Meters and flow stations: often 23 hardware, 25 objects, 26 power.
• Smoke control: life-safety sequences that 25 must not casually override.

How to read a dispute

Ask which drawing shows the signal and which specification paragraph names the owner. If neither does, the dispute is a specification defect, not a personality conflict. Related: what Division 25 coordinates and points and sequences.