Most bathrooms have some sort of ventilation system. Many people overlook the importance of proper ventilation in the bathroom. Your exhaust fan removes excess moisture and nasty odours, keeping mould and mildew from becoming a problem and keeping your air healthy. To keep it running its best check out these tips: 

  1. Clean your exhaust fan twice a year. Most exhaust fans have covers that simply pull off or are held on by just a screw or two. Remove the cover and clean the vent slots. Also, check the fan for dust build-up. Either brush or vacuum off any accumulation that may have attached itself to the fan. You’ll be surprised how much dust will be in your fan. Just a light covering of dust on the fan can reduce the fan’s performance by 20-40%.
  1. Keep the door or window open a bit. If the bathroom is sealed off tight while the fan is on, then the fan has no place to draw air from, thus it can’t put the moist air outside. No air flow into the bathroom will take away 90% of the fan’s power to exchange in the bathroom.
  1. After a shower, let the fan run another 5 minutes or longer.

Remember that the primary function of a ventilation fan is to get rid of moisture, so it's crucial that the unit be vented all the way to the outside of the house. Venting a fan into the attic simply takes the moisture from the room and puts it up into the attic, where it can do just as much long-term damage to your house - it's also a violation of the building codes.

Fans are available as a fan only; a fan/light, which combines an incandescent or fluorescent ceiling light with the fan; a fan/heat, which combines the fan with or one or two heat bulbs; and a fan/heat/light, which combines all three. You'll also have a number of options for how to control the unit, ranging from a single switch that turns on the fan and light at the same time to multiple switches that control each function separately. You can use a timer to ensure that the fan shuts off after a certain number of minutes.

Fan Placement
The aim of locating the fan is to get the air to flow across the room, without taking a shortcut and leaving an area unventilated. This means if there is a window; the air shouldn’t come in the window then straight to the fan without passing across the room first. It is really a matter of common sense. Put the intake as close to the problem as possible, which normally means over the top of the shower stall.

The Best Fan for Your Situation
There are really four things you need to be concerned about in the selection and installation of a bathroom ventilation fan - air movement capacity, noise level, ducting and optional accessories. Each plays an important role in the fan's proper operation.

 Air Movement Capacity
Fan exhaust capacity is rated in litres per second (L/s) or cubic feet per minute (cfm). A normal bathroom needs a good-quality fan that draws 25 L/s (50 cfm). A poor-quality fan won't exhaust enough air and will be too noisy for regular use. Large bathrooms, or those with bigger fixtures, such as spas, need larger fans. Place a bathroom fan as close as possible to the source of the moisture or odour.

Building Code Requirements (SUMMARISED)

  • What the Law States

    NZ Building Code G4 Ventilation (summarised):
    “...Buildings shall have a means of collecting or otherwise removing: cooking fumes and odours; steam from laundering, utensil washing, bathing and showering; odours from sanitary and waste storage spaces; poisonous or flammable fumes and gases...”

             Natural Ventilation for the above is acceptable as long as opening windows in each room have an area of 5% or more of the floor area of the room.

             For internal rooms without natural ventilation, mechanical ventilation (extraction fans) must be installed to extract the air at given rates. Where fans are used to remove moisture and other contaminants from kitchens, bathrooms and laundries in housing, the exhaust air must be ducted to the outside at the flow rates mentioned above.

             The above requirement for ducting also applies to any fan in those areas, even if there is an opening window (i.e. even if the fan is not a requirement to comply with ventilation          regulations, but is installed as an optional extra).

These are minimum Building Code requirements. Generally, this would not fulfill your expectations of moisture and odour removal. We recommend that you consider the following industry recommendations when choosing your fan.

Industry Recommendations

  • The ventilation industry has a “Recommended Air-Changes per Hour” solution. i.e. An air flow rate sufficient to remove/replace the total volume of air in a given room a specified number of times each hour. Obviously fans will not necessarily be left running for an hour – a fact which is taken into consideration in the formula.

What Size Fan?  (This is a general guide please call us for a quote or help with your calculations)

Choosing the correct size fan is vital for effective ventilation.
To determine the best size fan for your needs follow the calculation below:

Calculate the Room Volume in Metres:
Multipy:  Length x Width x Height = Room m3

Calculate Required Performance:
Multiply the room volume by the number of required air changes. Ten to fifteen air changes per hour is a good starting point, or view a more detailed table below.

Select Your Fan:
Select a fan with a performance rating at least 20 percent more than what you have calculated. It is better to choose a fan with a higher rating than have inadequate ventilation.

A domestic bathroom 3m x 2.5m x 2.5m = 18.75m3
Recommended air changes for a domestic bathroom = 10 - 1
So Multiply 10 x 18.75 = 187.5m3/hr
Add 20% = 225 m3/hr (225 divided by 3.6 = 62.5l/s)

Recommended Air Changes per Hour



Living Rooms










Kitchens - Hotel or Industrial




Kitchens - Domestic


Stores & Warehouses






Noise Levels
In order to be effective, a bathroom fan needs to be used and that usually won't happen if it's too noisy. For that reason, the second consideration in the selection of your fan should be the amount of noise it makes while in operation.

In addition to the l/s rating discussed above, ventilation fans also carry a noise rating, listed in dBA. Several things affect how loud or quite a fan is - its air-moving capacity, the type of fan blade assembly being used, how much insulation is placed in the fan housing, and where the fan is located. As you probably would expect, the quieter the fan is, the more you can expect to pay for it. Fans are a long-term investment, and the quieter unit is well worth the extra initial cost.

Installation and Ducting
Most fans are designed for direct ceiling mounting within the bathroom itself. There are also fans designed to mount in the wall, and fans, which mount in a remote location - up in the attic, for example -- to further cut down on noise.
There are two major types of extractor fans – axial and centrifugal. The difference between both types is power and method of installation.

Axial Flow Fans
Axial flow fans utilise a propeller type blade to move the air in line with the axis of the motor. They are very efficient at moving large volumes of air through walls or windows into free air but have a limited application where ducting is introduced.


Centrifugal Extractor Fans
Centrifugal fans incorporate drum type blades and move the air at 90 degrees to the axis of the drive motor. They do not achieve the same air volumes for a given power output as axial fans but generate much higher pressures which make them ideal for ducted installations



Fans, when connected to ducting, operate best when the ducting is installed so that any restriction to the flow of air are minimized. Fans can be mounted anywhere along the dust system but care should be taken as not to restrict the airflow.

  1. Maximise the distance between the fan and inlet/outlet grilles to reduce noise at grilles.
  2. Don’t leave ducting slack, extend flexible ducting fully, cut to correct length, remove bends where possible. Support the duct so that is its straight.
  3. Ducting should be the same size or larger than the fan spigot to optimize airflow. Don’t squeeze ducting into the fan spigot as this restricts the airflow.




Uniquely Airflow


Updated 14/05/2014 22:56:28