HVAC Design for Commercial Fitouts

What You Need to Know

Every commercial fitout needs HVAC design. The base building provides the central plant. Your fitout connects to it with new ductwork, diffusers, and controls that suit your layout. If the base building lacks capacity for your use, you need supplementary cooling or ventilation on top.

Offices need 10 L/s of fresh air per person (AS 1668.2:2024). Retail and food tenancies need more. Section J energy rules apply to every fitout with air conditioning. For a standard fitout (100-500 sqm), expect mechanical design fees of $3,000-$8,000. Complex tenancies like restaurants or medical centres run $8,000-$15,000+.

• Offices need 10 L/s of outdoor air per person. The minimum must not drop below 0.35 L/s per square metre of floor area, even with demand control ventilation. (AS 1668.2:2024)
• Retail shops need 10 L/s per person based on the design occupancy density. Shopping centres and malls have higher rates due to higher foot traffic. (AS 1668.2:2024)
• Meeting rooms and boardrooms often drive the peak fresh air load. At 1 person per 2 sqm, a 20 sqm meeting room needs 100 L/s of outdoor air. (AS 1668.2:2024)
• Kitchen and food prep areas need dedicated exhaust. The exhaust rate depends on the cooking equipment and hood type. Makeup air must replace the exhaust volume. (AS 1668.1, AS 1668.2:2024)
• Section J (NCC Part J6) applies to all fitout HVAC. Ductwork must be insulated and sealed. Fan power limits apply. Time switches must be fitted to systems above 2 kW cooling or 1 kW heating. (NCC 2025 Part J6)
• Supplementary cooling systems must not conflict with the base building. All systems serving one space need coordinated controls and the same temperature sensors. (NCC 2025, Base building services agreement)
• Toilet exhaust is the tenant's responsibility in most fitouts. Minimum exhaust rates apply per fixture. Fresh air must not be drawn through toilets into occupied spaces. (AS 1668.2:2024)

A typical office fitout in a Sydney CBD building starts with the base building. The landlord provides chilled water or a VRF system to a point on the floor plate. From there, the tenant's HVAC design covers fan coil units, ductwork, diffusers, and controls to suit the new layout. Open plan areas, private offices, meeting rooms, and server rooms each have different loads. A 300 sqm open plan office with 30 staff at 10 L/s per person needs 300 L/s of outdoor air. Add two meeting rooms at 50 L/s each, and the total fresh air demand hits 400 L/s.

Problems show up when the fitout layout does not match the base building grid. If the landlord's system was sized for 1 person per 10 sqm, and your fitout packs in 1 per 5 sqm, you may need supplementary cooling. This adds cost and complexity. It also needs careful control so the base building system and your add-on do not fight each other.

Retail fitouts face different challenges. A clothing store may only need the base building system extended. A food tenancy needs kitchen exhaust, makeup air, and grease filtration. The exhaust volume from a commercial kitchen hood can be 1,000-3,000 L/s, which must be replaced with conditioned makeup air. This often exceeds the base building capacity and requires a separate outdoor air unit.

The biggest risk in fitout HVAC is not checking the base building capacity early. If the central plant cannot support your loads, you find out too late. Request the base building services manual and mechanical drawings at the start of the project. Check the available cooling capacity, fresh air allocation, and any restrictions in the lease or building management rules.