Quick answer
- TAB proves CFM and pressures; Cx proves the system runs as designed.
- Light commercial still needs start-up + functional tests — scale the rigor to the job.
- Ambiguous “commissioning by others” is how finger-pointing starts.
When this applies
You are writing or reviewing an HVAC RFP
You need clear line items for TAB, start-up, and functional testing so bidders cannot exclude them quietly.
A new install “doesn’t feel right”
Hot/cold rooms, noisy registers, or economizers that never open — classic missing-balance symptoms.
Title 24 acceptance overlaps mechanical closeout
Coordinate acceptance tests with TAB/Cx so you do not pay twice for the same functional checks.
How it works
Define the minimum deliverables
For many light commercial RTU jobs: manufacturer start-up sheet, airflow verification (or full TAB where duct systems warrant), economizer functional test, thermostat/BAS point-to-point, and as-left setpoints.
Assign who hires TAB/Cx
Owner-direct TAB preserves independence; contractor-provided TAB can work if the report standard is specified. Say which model you want in the RFP.
Tie payment to report acceptance
Hold a retainage tranche until TAB/Cx punch items are closed. Reports should list deficiencies with responsible party and due dates.
Failure modes to avoid
“Balance by others” with no named others
The gap becomes a change order or an unfinished building. Name the party and the standard.
TAB after ceilings are closed with no access
Dampers you cannot reach cannot be balanced. Coordinate access panels and timing.
Paper start-up with no functional tests
A signed manufacturer form that never proves economizer or schedule operation is incomplete closeout.
Proof & local context
- • Our commercial bids state start-up, documentation, and balance coordination responsibilities up front.
- • We work with independent TAB when the owner requires it — and we still own our install quality.
- • CSLB #1056688 · South Bay + Central Valley · Perfection Guaranteed.
Next step
Guidance reflects light-to-mid commercial HVAC, refrigeration, and server/edge cooling practice across San Jose / South Bay and Central Valley (Hanford, Clovis) jobs. Not for hospitals or hyperscale data centers. Confirm site conditions, Title 24 path, and manufacturer data before bidding.
FAQs
Do small RTU swap-outs need full TAB?
Not always a full duct-system TAB. They do need verified airflow, economizer function, and documented start-up. Scale rigor to duct complexity and complaint risk.
What is the difference between TAB and commissioning?
TAB measures and adjusts flows. Commissioning verifies the system meets design intent — sequences, safeties, documentation, and training. Overlap exists; both matter.
When should TAB be scheduled?
After the system can run safely and controls are online, with access to dampers and terminals — typically near the end of mechanical work, before final occupancy finishes hide everything.