AHU Room Size Estimator
AHU rooms are often value-engineered too small, then services cannot be maintained. Reserve plant space early. These rule-of-thumb figures size the AHU room before a detailed HVAC layout is available.
| Conditioned area served (per AHU zone) | Indicative AHU room area | Min. clear access |
|---|---|---|
| Up to ~10,000 sq.ft | ~120–180 sq.ft | ≥1.0 m around AHU |
| ~10,000–25,000 sq.ft | ~200–350 sq.ft | ≥1.0 m + tube-pull space |
| ~25,000–50,000 sq.ft | ~350–600 sq.ft | Coil tube-pull + door access |
| Rule of thumb (overall HVAC plant) | ~3–5% of conditioned floor area | Per ISHRAE good practice |
Reserve roughly 3–5% of the conditioned floor area for HVAC plant/AHU rooms at schematic stage, with at least 1 m clear around each unit and space to pull cooling-coil tubes. Locate AHU rooms to keep duct runs short.
Verify — Rule of thumb only. AHU room size depends on the design airflow (CFM), unit configuration, fresh-air handling and coil pull-out space — confirm against the HVAC design and ISHRAE guidance.
Want this coordinated against your structure?
Send us your schematic and we'll mark up a coordinated services section — so your ceiling height and shafts survive detailed design. The other clearance guides, checklists and specification libraries are on the architects' hub.