Bathroom Exhaust Fans

Exhaust fan size is determined by airflow capacity, measured in litres per second (L/s) or cubic metres per hour (m³/hr). As a general guide, the Australian Standard AS 1668.2 recommends a minimum of 25L/s for bathrooms and 40L/s for larger ensuites with a shower and bath. To calculate the right size for your space, multiply the room's length, width and height, then match this to the fan's rated capacity, as a rule of thumb, look for a fan that can achieve 15–20 air changes per hour.

Yes. Exhaust fans involve electrical wiring and, in many cases, ducting through ceiling or wall cavities, so installation must be carried out by a licensed electrician to comply with AS/NZS 3000 (Australian Wiring Rules). If your fan is being installed in a bathroom, it will also need to meet the IP rating requirements for the relevant water exposure zone. Engaging a licensed professional ensures your installation is safe, compliant, and won't affect your home insurance or building certification.

Exhaust fans should always be ducted to the outside of your home, whether through the roof, eave or external wall, rather than exhausting directly into the roof cavity. Venting into the roof space allows moisture and humid air to accumulate, which can lead to condensation, mould and long-term timber or insulation damage. Proper external ducting is a requirement under the National Construction Code and is essential for protecting your home's structure over time.

Yes. An exhaust fan should always be ducted to the outside of the home, through the roof, an eave or an external wall, rather than left to discharge into the roof cavity. Venting into the roof space lets moist air settle there instead of escaping, which over time leads to condensation, mould and damage to timber or insulation. Ducting to the outside is required under the National Construction Code and is one of the most common things to check if an existing installation looks like it was done cheaply.

For most bathrooms, a ducted ceiling exhaust fan is the standard choice, since it removes moist air to the outside rather than just circulating it. Combination units that pair an exhaust fan with a light, or with a heat lamp, are popular where ceiling space is limited and only one fixture is wanted. Wall-mounted fans are an option where ceiling access for ducting isn't practical. The right choice mostly comes down to the room's layout and where the ducting can realistically run, rather than one fan type being universally best.

Removing and refitting the fan body itself is sometimes within reach for a confident DIYer if the replacement uses the exact same wiring connection and ducting as the old unit. However, any work on the electrical wiring, or a change in fan type or ducting path, needs a licensed electrician to comply with Australian wiring rules and the IP rating required for the bathroom's wet zones. Given the safety and compliance stakes, most people have an electrician handle the whole swap rather than splitting the job.

The best fit depends on room size and whether the fan needs to double as a light or heater. For airflow, match the fan's rated capacity in litres per second to the room's volume, AS 1668.2 suggests a minimum of 25L/s for a standard bathroom and closer to 40L/s for a larger ensuite with a shower and bath. Beyond capacity, look for a fan with a low noise rating (measured in sones) if it will run for extended periods, and confirm it carries the IP rating appropriate for where it sits relative to the shower.

They solve different problems. An exhaust fan removes moist, stale air from the room to prevent condensation and mould, which is a ventilation function required by the building code. A bathroom heater warms the room for comfort and doesn't move air outside. Many ceiling units combine both functions in one fixture, but they're still doing two separate jobs, and a bathroom with only a heater and no ventilation path won't meet the code requirement for moisture control.