by ericmark »
Fri Apr 21, 2017 7:58 am
What kbrownie says is correct, no need for me to repeat it.
Building regulations are not retrospective, however it would make sense to follow the current regulations.
So to switch with light switch is dependent on the window, with no window in the bathroom there is nothing wrong with using the light switch, also with an opening window there is no requirement for a fan so again nothing wrong with using a light switch.
However if there is a window, but it does not open, then there has to be another way to switch on the fan as well as the light switch, in fact there is no requirement to have it connected to light switch, so three main methods are:-
1) A simple push switch with built in timer.
2) A PIR.
3) Push switch plus lights.
For the latter you need a double pole switch, so although it is physically the same switch, electrically they are independent, other wise when you push the button the lights would also come on.
In the main fans ask for a 3A fuse, this will not protect the fan, it's far too big, if the fan was to stall and overload the fans windings would burn out before the fuse, British plug fuses have two preferred sizes 3 and 13 amp so they are telling you which of the two to use. Where a lighting supply is used the standard 6 amp protective device will likely trip before a 3A fuse will blow so no point fitting a fuse.
However where the fan becomes faulty, you will often need to disconnect the fan before you can reset a trip, so you do need an isolator so if it goes faulty you can switch off the fan and still have lights, since lights in bathrooms now need RCD protection you want a double or three pole isolator.
Bathrooms are a special location so if you want to be legal then the cost of going through the local authority building control will be higher than getting a scheme member electrician to do the work for you and he can self certify. Rules do alter around the country, Wales, England and Scotland are all different. So check for your area.
Main reason for fitting a fan is the double glassing no longer allows the window to open, however if the fan blows out, air needs to replace what it blows out, under I think Part F building regulations you can't fit a fan with an open flue, seems odd but open flue means the device draws air from inside the house, it does not mean you can stick your hand up the flue. So be it bathroom fan, cooker hob, or tumble drier first look at fires fitted in the house.
There is a way around the problem, there are heat recovery units made where the heat exchanger is built into the pipe going outside, so they look like a simple extractor fan, but instead of needing vents in the bathroom door to replace the air, the replacement air is drawn from outside, since outside air contains less moisture than inside air they work better than simple fan, although more expensive around £400.
The problem with a modern house is we have gone around stopping all the drafts, and you can't pump air out unless it can get in somewhere. I remember a bus with air vents which would keep passengers cool and the door opened in and could not be opened until fans were turned off.
Before you even think about wiring, have a look at house design and work out how that air gets back in.
