How much air do I need to exhaust from my bathroom and laundry?
The amount of air extraction required for a particular area is ultimately dependent upon the National Construction Codes (NCC). The NCC in conjunction with Australian Standard AS1668.2 specify the following minimum exhaust flow rates (Volume 1, Part F6.3):
- “An exhaust system installed in a kitchen, bathroom or laundry must have a minimum flow rate of-
- 25L/s for a bathroom
- 40 L/s for a kitchen or laundry
- Exhaust from a kitchen must be discharged directly or via a duct to outdoor air
- Exhaust from a bathroom or laundry must be discharged –
- directly or via a duct to outdoor air or
- to a roof space that is ventilated in accordance with Clause F6.4.”
Do I need to duct my range hood outside?
Yes, the NCC (2019) dictates that the kitchen exhaust system must be ducted to the outside.
What type of fan should I buy?
There are essentially 3 main categories of exhaust fans for domestic ventilation.
Cost effective ventilation solution. Requires an electrician to install fan. Only designed to exhaust very short distances (eg through a wall). Often a noisier solution to other fan types due to the location of fan motor being inside the bathroom.
Another cost effective solution. These fans have several advantages:
- They are generally supplied with a plug and lead so are DIY friendly.
- They are easy to maintain and or replace
- Ceiling fans generally have a centrifugal motor (as in Expella’s ceiling fan) which has good performance when connected to ductwork. The larger fan blades mean the fan motor spins at a lower frequency and is a quieter alternative to a wall fan.
Inline fans offer the best all round performance and noise solution out of all the fan types. The inline fan is located inside the ceiling space and the motor is not directly exposed to the bathroom.
These fans also allow for a variety of discreet grille options to minimise any disruption to the bathroom design. If installing an inline fan we recommend choosing a fan with a centrifugal or mixed-flow motor/ impeller.
Where is the best place to locate the fan or grille?
The position of the fan or the intake grille is very important. The aim is to generate as much air flow around the room as possible without creating a short-cut for the air and hence an area of no circulation. Therefore the fan or grille should be placed as far away from the replacement air source as possible. Air replacement should also be considered via a door grille or a gap underneath the door.
It is important to locate the discharge point in an area that is protected from extreme weather conditions (wind). This may create additional pressure on the fan.
Can I vent my bathroom or laundry exhaust into my roof space?
It is illegal to ventilate bathroom air directly into a ceiling space, unless the ceiling space is sufficiently ventilated in its own right. The reason for this is that the moist air from the bathroom and or laundry promotes rot, destroys insulation and can warp the ceiling panels.
What type of ducting should I use?
Ducting has a major impact on the performance and efficiency of a ventilation system. Common types of ducting include:
– Rigid Metal Ducting
– Rigid PVC Ducting (round or low profile)
– Flexible ducting
Rigid plastic ducting provides the most effective option in terms of installation costs, performance and noise. Rigid plastic pipe is becoming more common, but consideration must be given to fire compliance. Approved Expella Odour Control systems have been appraised for the use of plastic pipe and have been deemed to satisfy all relevant codes.
Duct sizes should be maintained at the largest possible size. The duct diameter should not be smaller than the fan outlet. A small difference in duct diameter can significantly affect the air flow and pressure loss. Generally, the relationship of the diameter and pressure loss is inversely proportional to the power of 4. For instance if the duct diameter is halved, the potential pressure increase is multiplied by 32.
Who can install the Expella ventilation kits?
With the exception of the Wall and Roof mounted exhaust kits, any competent DIY handyman can install Expella’s inline or ceiling exhaust kits.
All Expella’s products have been sourced or designed with particular attention to the ease of installation.
The Wall and Roof fans are required to be hard wired and must be installed by a licenced electrician.
Do I need to have subfloor ventilation?
Yes, however you may not require ventilation by mechanical means if you have sufficient subfloor vents (openings) evenly spaced to create cross flow ventilation. If cross flow ventilation cannot be created passively using vents on opposite walls, you may need to consider mechanical ventilation. The NCC Volume 2 Part 3.4 clearly outlines the requirements for subfloor ventilation and the reasons why below:
“Ground moisture rising into or entering the subfloor space can create a damp environment which encourages timber rot, fungus growth and the potential for termite activity. Subfloor ventilation increases air flow, reducing any damaging water vapour in the subfloor space.”
How do I understand fan performance and fan curves?
Fans are always characterised by air flow volume, generally the maximum exhaust rate is at free air (measurement taken when no ducting is connected to the duct).
To ensure sufficient ventilation is provided for a particular application, it is essential that the correct size of fan is selected. Fan selection depends on fan performance and its application.
Fan curves are used to illustrate the performance of a fan against static pressure or resistance which is caused by ducting, bends and grilles. This means that if the pressure that the fan must overcome is known, then one can reasonably ascertain the airflow rate. The problem is calculating the pressure caused by the length of duct, bends and grilles.