What capacity fan to use in bathroom?

[JamesHughes]

(Repost as used wrong title before)

Our bathroom revamp is going to include an extractor - the room currently doesn't have one. However, I am having trouble deciding what to go for.

It will be wall mounted, two layers of brick to the outside wall so a very short duct. Will use a timer system plumbed in to the lighting circuit, via 30mA RCD and three pole isolator. (Yes, I know I need to get this certified/done by Part P person - for the 8inches of wire that will be actually be in the bathroom!)

The room is 14.5m3. I have read varying advice for what capacity of fan to get. This room will have a shower in, so some advice is 15-20 times the volume - which would mean a fan of 215m2/hr. Other advice would indicate less than that = such that 85 or so would be sufficient.

Manrose do some at that level (230m3/hr) at 150mm duct size, which does seem pretty beefy. They also do many at the 85 level seemingly aimed at bathrooms.

After all that intro, all I really want to know is - is 230 overkill, and should I just stick with around 85m3? Are Manrose a decent enough make? They seem cheaper compared with the others.

TIA

James

 

[holmslaw]

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[JamesHughes]

Fantastic - thanks.

Should be plenty of intake area - bricked up fireplace with airbrick and a loosely fitting door! (It's an old house!)

James

 

[holmslaw]

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[ricicle]

You must also provide supply air for the extract to work efficiently, easiest way is to have a 10mm ish gap at the bottom of the bathroom door.

At last, someone who understands the need for make up air when extracting air from a room.

(Pretty basic I know, but the trouble I had trying to convince a design team when planning a spray shop in our new factory )

 

[LiamPope]

You need 6 - 8 air changes per hour, so your 85mts/hr fan will do the job.

The 230mts/hr job will pull you're wig off.

You must also provide supply air for the extract to work efficiently, easiest way is to have a 10mm ish gap at the bottom of the bathroom door.

Er, given his 14.5m3 room volume, I get 87 - 116 for 6 - 8 air changes. But then where did you get 6 - 8 air changes from? Reccommendations for a bathroom with a shower are 15 - 20 changes. OP - a piddly 85m3/hr wall mounted fan might be within the absolute minimum allowed, but unless you like your ceiling/walls dripping with condensation after a shower, dont wish to be able to see through your mirror for steam, and enjoy mould, I'd be going with the upper end of sensible recommendations - so 200+ m3/hr. 230m3/hr wont pull the wig off a housefly.

Have a play with the fan calculator on TLC. My bathroom is slightly smaller than yours and I fitted this...

http://www.tlc-direct.co.uk/Products/SLTDK250T.html

...and it's great. Room is just about nice and dry after a shower - wouldn't want extraction any weaker. Also, the beauty of a loft mounted ducted fan is that all you have in your bathroom is a discrete apperture on the ceiling, you can barely hear the fan at all, and all the wiring is in the loft, so you dont have to worry about notification. Much, much better all round and more than worth the money.

Liam

 

[holmslaw]

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[ban-all-sheds]

Dunno about Googling, but 87 - 116m³/hr is 24 - 32l/s....

 

[electronicsuk]

I'd fit the largest sensible fan you can, within the limits of cost and aesthetics, of course. If you find the extraction rate too high, it wouldn't be a major task to fit a speed controller and slow the fan down. However, if the fan is too small, you'll be taking it out and replacing it again, along with possibly installing a larger duct.

 

[ban-all-sheds]

I can't imagine any domestic bathroom extractor fan being too powerful...

 

[LiamPope]

I think you will find you're getting flow rates mixed up with air changes per hour. Recommneded flow rates are 15 - 20 litres per sec.

Try googling - shower room air changes per hour - then tell me I'm wrong .

I'm sure I'm not getting mixed up, but maybe you are?

I'm going on, for example, this information:

http://www.tlc-direct.co.uk/Technical/Ventilation/Ventilation4.html

...and at the time I was specifying a fan for my bathroom I found similar recommendations on many sites.

I'm also going on the fact that I have installed a 250m3/hr fan in my bathroom and am satisfied with the performance, but certainly wouldn't want any less. And also the fact that I've been in countless bathrooms with piddly little fans that are like steam rooms after a shower.

The minimum allowed is 15l/s (54m3hr), which is a bit silly because how many air changes (which is what matters) 15l/s relates to is entirely dependant on the size of the room. By all means base a reccommendation on this bare minimum figure, but the recipient of the advice better really like a dripping wet bathroom! As I said, sensible advice to achieve a decent result would be to err towards the higher end of recommendations. That is 15-20 air changes per hour (not litres/sec) in all sources I've seen. I've only seen as low as 6-8 recommended for a bathroom without a shower, but the bathroom in question here has a shower.

 

[holmslaw]

..

 

[LiamPope]

Here's a couple...

http://www.simplifydiy.com/electrical/extractor-fans

http://www.thediyworld.co.uk/the_bathroom.html

I'm not your dog though - look yourself. I'm not trying to have an argument either - I'm just reporting what I've read, which also happens to be supported by my personal experience. I'm sure you can find lower recommendations, and indeed the minimum allowed by the regs is merely a fan which can provide 15l/s (54m3/hr). The regs are woefully inadequate though, in my experience - there's a big difference between meeting them and actually achieving a bathroom that stays dry while you have a shower.

An 85m3/hr fan is pretty much the smallest available, so yes it meets regs, but do you really think the smallest fan available is going to offer decent performance? As I said most bathrooms I've been in with one of those have been dripping wet after a shower. On the other hand, I've fit a 250m3/hr fan, and the performance is excellent. My bathroom stays dry and I dont even need the heated mirror I installed which I thought would be a god-send for shaving given my experience in other bathrooms with crap fans.

At the end of the day it's up to the OP - he can go for the smallest fan available which meets the bare minimum requirements of regs, or he can choose not to ignore reccommendations that suggest something much more powerful, and end up with something that does a decent job. Similarly you can do whatever you want - I dont really care.

 

[ricicle]

I personally would go for the best quality/biggest air mover I could afford. The more steam/stink shifted from the bathroom the better.
I hate waiting for the mirror to de-fog so I can have a shave (nobody suggest shaving before shower)

 

[ban-all-sheds]

(nobody suggest shaving before shower)

OK.

Grow a beard.