1.
Where? The single most important consideration, because it is the one which could have fatal circumstances, is the fan's location - where should you situate the fan? The bathroom, unlike any other room in the house is characterised by the primary use of water.
As we all know, electricity and water do not make happy bed fellows.
For this reason one must take extra special care about the type of fan they are to install.
In most countries strict laws govern the installation of electrical items in the bathroom.
In the UK, for example, the bathroom is divided into zones relating to how close one is to the bath, shower and sink.
The zones nearest to one of these water dispensing items require the installation of a low voltage or IP rated fan.
SELV (safety extra low voltage) fans, which run at 12 volts, protect the user because the current is radically reduced from full mains voltage by the use of a transformer which is housed outside the bathroom - in the wall or ceiling for example.
Should anything go wrong with the wiring the user will feel a sharp prod...
Unpleasant enough, but definitely preferrable to receiving 240 volts.
IP rated fans ('Ingress Protected') prevent water getting into the electrical motor of the fan.
This means that they do not have to be SELV and consequently do not require a transformer.
They are therefore far easier to install and the homeowner does not have to worry about where to situate the fan.
However, currently, there is only one fan on the market, the Airflow QT100, which meets the strict requirement of being IP*5 rated.
2.
Duct Run The most often overlooked aspect of fan installation and the one which, by a huge margin, causes most problems after installation is the length of duct run.
Without doubt this is the biggest cause of bathroom fans being replaced incurring the cost of an extra visit from an electrician and re-decorating or re-tiling.
Why?! Almost all bathroom fans use axial technology.
Axial technology is great because it is cheap and in most installations where the fan is to be ducted less than one foot straight through an external cavity wall to the outside world will operate perfectly.
Axial fans however have a problem with pressure and air pressure builds up significantly in the length of duct.
In fact in as little as four metres most axial fans will extract at less than half of their stated extraction rate..
! In other words, unless your duct run is less than, at most three metres an axial fan is useless.
For these installations you will require a centrifugal fan.
These use an entirely different technology and some models, such as the Vent Axia Solo can operate at 75% capacity on duct runs up to 50m! Centrifugal fans are available in two types: either as a wall mounted version, which doesn't look any different from a standard axial fan, or as an inline fan.
An inline fan has two essential differences and cannot be mistaken because it has both an extract or intake funnel which, in layman's terms sucks the air out of the bathroom and an exhaust funnel which sends the stale air to the outside grille and expels it.
Firstly, as its name suggests it sits in the middle of the length of duct,..
or 'in line'.
This means consequently that secondly, it is not situated at the point of extraction.
In other words the fan is housed in the ceiling and not in the bathroom.
The only thing you will see in the bathroom is a ceiling grille.
In using an inline centrifugal fan you therefore benefit not only from a more powerful fan but one which in no way can come into contact with water.