Extractor Fans

personally I would say get one in each room. I presume your talking about the electric extractor fans? My son had to have one installed in his bathroom as it was so damp the walls were black. I was told you could do it yourself if you know what you are doing but as his was a flat it was a bit more difficult so got someone in . Cant really help on price though as we had the bathroom tiled and a shower fitted so it was all included in the price. Be aware though if you do it yourself there were some new regs out last year or so which means that electrical work carried out thats extra especially in bathrooms is supposed to be approved by local authority or something like that if you are not an approved electrician. Dont know if people actually do this or not but its something to take into consideration. (see link here http://www.direct.gov.uk/HomeAndCommunity/Planning/BuildingRegulations/BuildingRegulationsArticles/fs/en?CONTENT_ID=10014171&chk=UFKK%2BB)

on the plus side it does seem to have helped in my sons bathroom!

I would ask 3 electricians to quote. If they can't make the holes then they will bring in someone else but include it in the quote.

With the new regs you are supposed to have a a part P qualifed engineer under the govs stupid new regs. You may wish to consider a humidistat fan esp in the bathroom. Essentially you can hav a fan with pullcord, requires you to turn on off. Fan with timer comes on with light, requires light to be switched on even in summer and runs for usually varible time after. This will also come on if you go wandering in the middle of the night. Fan with humidistat, fan monitors relative humidity of room turns on when needed and off when extracted, be aware when first fitted can run for a few days constantly, that is how much moisture is in the room. The latest generation fans also have PIR sensors, which switch on when they detect movement. These also need to be ducted and be aware of potential backflow issues with the wind, depending on the siting. Always remember use the minimum lenght of ducting possible and fan will work most efficiently.

Assuming that you want the fan to get rid of condensation you wont know how long this will take so get one that has a Humidistat, if its not humid enough its not going to run and so wont cost you electric.

What sort of windows do you have in your bathroom? Mounting a fan in the window would save the trouble of knocking a hole in the wall.

You can also install a separate pull cord for the fan. That way you can control it independantly of the light. This is what I did, but bear in mind Part P wasn't around back then and now the regulations are more restrictive, especially where electrical works in bathrooms or kitchens are concerned.

I initially had a fan with a timer, bought as the humidity controlled ones were too expensive. You set how long it runs after it's switched off and this was fine for me.

However, when that failed, I replaced it with one without a timer as it was cheaper still. I now simply leave it running after I've used the shower, then turn it off later.