How long does HVAC design take for a commercial fitout?

For a standard commercial fitout under 500 sqm, allow 2-3 weeks from receiving complete architectural drawings to issuing design documentation. This includes load calculations, equipment selection, duct layout, and Section J input.

Can HVAC design be done faster?

Yes, rush turnaround is possible on most projects. Expect to pay 20-50% more for expedited delivery. The main risk is reduced time for coordination with other consultants, which can lead to clashes during construction.

What causes delays in HVAC design?

The most common cause is incomplete architectural drawings or changes to the design brief after work has started. Design changes mid-project can add 2-4 weeks. Providing complete floor plans, sections, and a clear brief at the start is the single best way to keep the timeline short.

How Long Does HVAC Design Take for a Commercial Building?

Section 1

The Short Answer

HVAC design for a commercial building takes anywhere from 2–3 weeks for a small fitout to 2–6 months for a multi-storey development. The biggest variable is not the engineering work itself. It is the completeness of the information you provide at the start. Projects that begin with full architectural drawings and a clear brief move through design quickly. Projects with incomplete information stall.

Section 2

Typical Timelines by Project Type

1

Small Commercial Fitout (under 500 sqm)

Office, retail, or cafe fitout. 2–3 weeks from receiving complete architectural drawings to issuing documentation. Includes load calculations, equipment selection, duct layout, Section J input, and specification.

This assumes drawings are complete and the brief is clear. Missing ceiling plans or late changes to the layout will push this out.

2

Medium Commercial (500–2,000 sqm)

Multi-tenancy office, large retail, restaurant, gym. 3–6 weeks. More complex systems (VRF, central plant, kitchen exhaust) require more coordination with other disciplines. Full CC documentation set.

Coordination with hydraulic, electrical, and fire engineers runs in parallel but adds review cycles.

3

Multi-Storey Development (2,000+ sqm)

Mixed-use, residential towers, large commercial. 2–6 months depending on project program. Central plant design, riser coordination, BMS specification, and staged documentation across DA, CC, and construction phases.

These projects run to the overall project program. The engineering timeline depends on when architectural packages are issued at each stage.

Section 3

What Affects the Timeline

Completeness of architectural drawings – the single biggest factor. Missing floor plans, sections, or ceiling layouts stop design work until they arrive.
Number of design iterations – each round of changes adds 1–2 weeks. Locking the layout early keeps the timeline short.
Specialist systems required – kitchen exhaust, car park ventilation, smoke exhaust, or clean rooms each require separate calculations and documentation.
Coordination with other consultants – structural, hydraulic, electrical, and fire engineers all share the same ceiling void. Coordination takes time but prevents clashes on site.
Certifier review cycles – responding to PCA or certifier comments can add 1–2 weeks per round.
Section J compliance documentation – adds 1–2 weeks if done as a separate task rather than integrated into the design process.
Multi-discipline packages – mech + hydraulic + electrical + fire takes longer overall but is more efficient than engaging each discipline separately.
Rush jobs – possible on most projects, but expect to pay 20–50% more for expedited delivery. The main risk is reduced coordination time.

Section 4

The Design Process Step by Step

1

Briefing and Site Visit

Review architectural drawings, confirm the brief, and visit site if needed. Identify constraints: ceiling void depth, plant room locations, structural limitations, existing services.

2

Load Calculations

Heating and cooling load calculations for every zone. These determine equipment capacity and are the foundation of the entire design.

3

System Selection

Choose the right system type for the building: split systems, VRF, chilled water, packaged rooftop units. Selection depends on building size, budget, energy targets, and maintenance access.

4

Duct and Pipe Layout

Design ductwork and pipework routes. Size ducts for air velocity and pressure drop. Coordinate routes with other services in the ceiling void.

5

Documentation and Specification

Produce drawings (plans, sections, details, schedules) and a written specification. This is what the contractor prices from and the certifier reviews.

6

Coordination

Cross-check with hydraulic, electrical, fire, and structural drawings. Resolve clashes before they become problems on site. This step prevents costly RFIs during construction.

7

Certification

Submit documentation for CC or CDC certification. Respond to certifier comments. Issue final documentation for construction.

Section 5

Who Needs to Know What

Section 6

References

National Construction Code 2022, Section J — Energy Efficiency
AS 1668.2:2012, The use of ventilation and airconditioning in buildings — Mechanical ventilation in buildings
AS 4254.1:2021, Ductwork for air-handling systems in buildings — Flexible duct
AIRAH, Best practice guidelines for HVAC design documentation