Gym HVAC Design: AS 1668.2 Rates + Cooling Loads

What You Need to Know

Gyms are one of the most demanding HVAC applications in commercial building design. A person exercising generates 400 to 600 watts of metabolic heat, compared to 120 watts for a seated office worker. That is 3 to 5 times the heat output per person. Combine that with high occupancy density, large glass facades, and moisture from sweating occupants, and you have a space that needs far more cooling, ventilation, and humidity control than a standard commercial fitout.

Under AS 1668.2:2024, exercise areas need 10 L/s of outdoor air per person. With a typical gym occupancy density of 1 person per 5 sqm, a 500 sqm gym floor needs ventilation for 100 people, which is 1,000 L/s of outdoor air. Group fitness studios push this even higher with densities of 1 person per 3 sqm during peak classes.

Mechanical engineering design fees for a gym fitout typically range from $5,000 to $15,000 depending on the size and complexity of the facility. Multi-level gyms with pools, saunas, or commercial kitchens sit at the higher end.

• Exercise areas require 10 L/s of outdoor air per person. Design occupancy density for gym floors is typically 1 person per 5 sqm. Group fitness studios may be 1 person per 3 sqm during classes. The minimum outdoor air rate must not drop below 0.35 L/s per square metre of floor area. (AS 1668.2:2024)
• Change rooms and shower areas require dedicated exhaust. This air cannot be recirculated to other spaces. Exhaust rates are based on the number of fixtures and floor area. Change rooms typically need 10 L/s per square metre of floor area or per shower/bath. (AS 1668.2:2024)
• Pool areas require dehumidification. If the gym includes a lap pool, plunge pool, or spa, the pool hall needs a dedicated air handling system with dehumidification to control moisture and prevent structural damage from condensation. (AS 1668.2:2024)
• Section J energy efficiency rules apply to all gym 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. Economy cycles are mandatory for systems above certain capacities. (NCC 2025 Section J)
• Indoor air quality must meet Part F6 requirements. CO2 levels in occupied zones must not exceed 850 ppm above outdoor ambient. During peak gym hours with 100+ occupants, this requires the ventilation system to operate at full capacity. (NCC 2025 Part F6)
• Refrigerant charge limits apply in occupied spaces. VRF and split systems serving gyms must comply with AS/NZS 5149 refrigerant charge limits based on room volume and refrigerant type. High-occupancy spaces have stricter limits. (AS/NZS 5149)
• Noise levels must suit the activity. Main gym floors and group fitness studios tolerate higher background noise (NC 40 to 45). Yoga and pilates studios need quiet conditions (NC 30 to 35). System selection and duct sizing must account for these differences. (AS/NZS 2107:2016)

The most common mistake in gym HVAC design is undersizing the cooling system. Designers who use office load assumptions calculate cooling at 80 to 120 W/sqm and end up with a system that is 50% too small. A gym floor with exercising occupants, lighting, and solar gains through glass facades can hit 200 to 350 W/sqm in cooling load. For a 500 sqm gym, that is 100 to 175 kW of cooling, compared to 40 to 60 kW if you used office assumptions.

Humidity is the second major challenge. A gym with 80 people exercising at moderate intensity generates roughly 40 to 60 litres of moisture per hour through perspiration and respiration. Without humidity control, this moisture condenses on mirrors, windows, and cold equipment surfaces. The target is 40 to 60% relative humidity. In Sydney's humid climate, this often means the HVAC system needs active dehumidification, not just cooling.

Zoning matters more in gyms than in most commercial spaces. The main gym floor runs at near-constant load during operating hours. Group fitness studios swing from empty to packed in minutes, with 30 to 40 people generating extreme heat in a 100 sqm room for 45 minutes, then nothing for 15 minutes before the next class. The HVAC system needs to respond to these rapid load changes. Variable speed drives on fans and compressors are essential for group fitness zones.

Change rooms and showers need separate exhaust systems. AS 1668.2:2024 prohibits recirculating air from wet areas back into the gym. The exhaust creates negative pressure in the change rooms, which prevents odours from migrating to the gym floor. The makeup air for these exhaust systems must come from the general gym ventilation, not directly from outdoors, to avoid pulling unconditioned air into the building.

Reception and office areas within the gym are standard commercial loads. These spaces should be on a separate zone with their own thermostat. Putting the reception on the same system as the gym floor means it will be overcooled when the gym system runs at full capacity during peak hours.