Extractor Fan Wiring and Setup Q&A

Fan Wiring Q&A - Setting Up and Wiring Extractor Fans In The Home
Please note - These are the most common questions that our customer service team are asked on a daily basis about extractor fan wiring and setup. Some of this information is given to aid understanding of some of the most common fan wiring issues - We would always recommend that any wiring in the home is done by a suitably qualified electrician as there are very real dangers and stringent laws associated with the majority of electrical work.
Question: I bought a timer fan to replace a standard fan, why won't it work?
Answer: Usually this due to the original standard fan only having a single live connection. Most timer fans (and fans with other automated options such as humidistats and PIR sensors) require an additional permanent live cable to make the timer function work. This type of fan uses a switched live to activate the fan on first use and then when this circuit is broken (i.e. the fan is switched off with the light for instance) then the other 'permanent' live provides a feed to the fan in order that it can run on for the duration that the timer has been set to. The fan cannot be used unless the extra live is provided or the timer function is completely linked out (see below).

There are some exceptions to this rule, for example, the Airflow Quietair timer, humidity and sensor fans will work without the additional permanent live its just the over-run timer won't function.

Question: How can I get my timer fan to work when I only have 1 live cable and a neutral?
Answer: Most timer fans can be fitted to a circuit with only a single live if the permanent and switched live terminals on the fan are 'linked'. This will allow the fan to run in a straightforward on/off operation only, the timer will not activate. This should only be attempted by an electrician after first consulting with the manufacturer of the fan.

Question: I have just had my humidity fan installed and it's continuously running and it won't turn off
Answer: Most humidity controlled fans leave the factory with the adjustable humidity stats  pre-set (sometimes as low as 40% RH), it may well be the humidity in the area that you live in is higher than the factory setting thus resulting in the fan running continuously. Simply increase the humidity stat setting to the required level of relative humidity. We advise starting at full (usually 90%) and working back down in small increments until you are happy with the fans response to turning on the shower etc. Please also be aware that unless your house is completely 100% sealed, then increases in external humidity levels during the year will also have an effect inside your house, so you may need to adjust the fan setting every 6 months or so.

Question: How do you wire a fan so that it comes on with the lighting circuit?
Answer: Pretty much any extractor fan (continuous running fans are usually set to run at a very low speed when the light (or remote switch) is off can be wired to be switched on/off at the same time as the light in the room. In simple terms, the light source is wired between the 'switched live' and the 'neutral' on the input side of the fan (or more likely the fan isolation switch to comply with regulations).

Question: Are 2 Speed (or multi-speed) fans more difficult to wire?
Answer: Not necessarily, but you do have to pay close attention to the manufacturer's fan wiring diagrams. You have a choice of terminals to wire to for one speed and another set for the higher speed. The complications can arrive if you wish to be able to externally switch the fan between speed 1 and speed 2. This will usually require the wiring in of an additional switch that will alter the speed (with a separate pull cord for example switching the fan on/off). It is also possible to buy a 3 position switch that has a centre off and then a speed 1 and speed 2 setting so that fan can be controlled from just one switch. You can further complicate things by adding a lighting circuit and timer facility. This is why qualified electricians have to spend a long time in the classroom and on courses learning all the possible permutations and how to confidently read some of the more complicated wiring diagrams. It is also worth noting that 'having a stab' at the wiring of extractor fans can not only be dangerous but also risks damaging the fan circuitry, so that when it's eventually rewired correctly it may still not work.

Question: How are Continuous or DMEV fans used?
Answer: Continuous running fans are usually set to run at a very low speed when the light (or remote switch is off) and then go into 'boost' mode (higher fan speed) when the circuit is activated. In continuous mode, the fan provides gradual replacement of air very quietly and with a small amount of energy. The boost function helps to remove humidity and stale air when a room has been recently used for showering, bathing, tumble drying etc..

Question: How do I keep fan noise as low as possible?
Pick a fan with low decibel levels (Vent-Axia Silent, Airflow Quietair etc..)
Be aware that fully tiled bathrooms can act as an amplifier for any noise present.
Use an in-line fan in the loft or void if possible (Airflow Aventa, Vortice Lineo etc..)
Use the lower fan speed setting on inline mixed flow fans as often high speed is overkill in standard sized bathrooms
Cushion the fan mountings - Many contractors use cut up pieces of mouse mat under the in-line fan mountings to reduce vibration noise transferring through the joists.
Extreme noise reductions - It is not uncommon for in-line fans to be 'wire suspended' in some lofts so that vibration issues are taken out altogether.
Consider using acoustic, insulated ducting.

View the extractor fan section of the Fastlec website