The single most important aspect of an extractor fan is, of course how much air it sucks out of the bathroom. Known as the ‘extraction rate’ the amount of air actually moved is described using two units of measure: metres cubed an hour (m3/hr) or Litres per second (L/s).
Now I’m not saying manufacturers deliberately make it difficult for end users to assess the relative power of different extractor fans, but they certainly don’t make it easy either! Some quote extraction rates using m3/hr while others uses L/s. Very rarely, unfortunately, do they quote both, making it difficult to compare models.
In order to convert the numbers, simply multiply m3/hr x 0.277.
There is a fairly complex calculation using the volumetric capacity of a room and number of ‘air changes per hour’ which will give you the exact ‘required’ extraction rate. However, in the real world this is rarely necessary and as a pretty good rule of thumb, for an average sized domestic bathroom you should be looking for an extractor fan offering at least 21L/s or 75m3/hr.
However, the better extractor fans now available offer 26L/s or 95m3/hr. For the small premium that these fans attract, the higher extraction rate is definitely worth it, clearing steam from the bathroom much more quickly. If a manufacturer or reseller does not make the extraction rate readily available don’t buy it – it’s being hidden for a reason.
Install the correct bathroom fan for the situation
This may sound obvious but it is amazing how often an extractor fan is asked to do a job it wasn’t designed to do. The most common problem is that of the fan being ducted over too long a distance. Long duct runs are a problem for extractor fans, as air pressure increases with every centimetre of ducting. Air pressure acts as an invisible barrier to the air being pushed along the duct – the longer the duct run, the greater the air pressure, the greater the resistance.
Standard axial fans should be ducted no further than four or five metres and the duct run should be kept as straight as possible because bends and kinks increase the air pressure and resistance. Any further than 5m – and a lot less if the fan is not particularly powerful (80m3/hr) in the first place, then the extractor fan will simply cease to work – the vented air will back up in the ducting and steam will remain in the bathroom.
If your installation requires a longer duct run you must use a centrifugal fan. The impeller design of centrifugal fans is such that they generate much greater air pressure. They also tend to be more powerful – the average four inch centrifugal fan vents at around 110m3/hr (compared to 95m3/hr for a top end axial fan). It may be said that centrifugal fans blow as hard as they suck!
Always, always have your bathroom fan installed by a Fully Qualified Electrician
This doesn’t need too much explanation, but it’s worth elaborating a little. We found that in 97% of cases where an extractor fan was deemed to be faulty or not working correctly it had been installed by the home owner (or friend/father/son etc etc) and not by a qualified professional.
In my humble opinion this is fairly conclusive but let’s consider something way more important – Electricity, whether delivered at 240v or 110v is potentially lethal – it can kill you. Incorrectly installing an electrical item is extremely dangerous both for the unqualified installer and *anybody* who thereafter uses the device. Any danger is multiplied ten-fold in the bathroom where water is present.
In short: always, always have your bathroom extractor fan installed by a Fully Qualified Electrician.