Outdoor Air Intake Location and Separation Distances

What You Need to Know

Where you put the outdoor air intake matters as much as how much air you bring in. AS 1668.2 sets minimum distances between air intakes and pollution sources like exhausts, cooling towers, and roads. Place the intake too close and you pull contaminated air into the building. Get it wrong and the certifier will reject it.

• Outdoor air intakes must be at least 6 m from most exhaust discharges. Distances vary by exhaust type and flow rate, with higher-contamination sources requiring greater separation (AS 1668.2:2024, Cl 3.10 and Table 3.4)
• Intakes must be separated from cooling towers per AS/NZS 3666.1. Industry practice is at least 6 m, but the required distance depends on tower type, capacity, and orientation (AS/NZS 3666.1-2011, Cl 3.4)
• Intakes must be at least 3 m above any trafficable surface. Higher placement is better, especially near roads, loading docks, or bin storage areas (AS 1668.2:2024, Cl 2.3)
• Intakes must be separated from sewer vents and car park exhaust discharges. Car park exhaust typically needs greater separation than general exhaust (AS 1668.2:2024, Cl 3.10)
• Kitchen and laboratory exhaust discharges need greater separation from intakes than general exhaust, based on dilution requirements (AS 1668.2:2024, Cl 3.10.3)
• All mechanical ventilation systems must comply with AS 1668.2, which references AS 1668.1 for fire and smoke control aspects of intake and discharge locations (NCC 2025, F6D6)

Picture a 10-storey commercial building with a rooftop plant area. The AHUs (air handling units) sit on the roof and draw outdoor air through intake louvres. The cooling tower is also on the roof, along with toilet exhaust fans and a kitchen exhaust stack from the ground floor tenancy. Every one of these sources needs clearance from the outdoor air intake, typically 6 m or more.

On a tight roof, 6 m in every direction is hard to achieve. The cooling tower goes in one corner, so the intake louvres need to sit on the opposite side. If the prevailing wind blows from the cooling tower toward the intake, the problem gets worse. Legionella-laden drift from a cooling tower entering the air intake is a serious health risk, so getting this distance right is not optional.

For buildings with intakes on the facade instead of the roof, the minimum height rule applies. A louvre at street level will not comply. Most facade-mounted intakes sit at Level 1 or above (at least 3 m up), which pushes the ductwork run from the louvre up to the plant room. That adds cost and ceiling void space. If the building is next to a busy road, the intake should face away from traffic where possible. AS 1668.2 does not set a specific distance from roads, but good practice is to keep intakes away from heavy vehicle areas and loading docks.