Extractor fan size needed

[shd1970]

Hi there,

Can anyone confirm the exact air changes per hour required for a UK bathroom please as per building regs as i am looking to get one fitted ?
Size of the bathroom is 2.1 x 2.7 x 2.3m = 13m3
I've read everything from 4 ACPH right up to 10 hence, i'm a little confused

The bathroom has 3 x opening windows

thanks in advance

 

[^woody^]

Extension, refurb, new build? Application date - for the appropriate regulation in force?

In any case you are better off not thinking about a fan in isolation and just in terms of air changes, but the type, position and controls and in accordance with BS 5250 which is a greater standard than building regulations - especially if you are trying to solve (or prevent) a problem.

 

[shd1970]

Hi @^woody^

It’s for my bathroom of which it’s a 1970s build which we’ve owned for 20 years and it’s never had an extractor in it to date and still doesn’t embarrassingly so guess from your list that that falls under refurb
The fan will be fitted in the loft and exhausted to a roof tile vent with appropriate insulated pipe being a cold area with a condensation trap

 

[^woody^]

You don't need to comply with building regs, but that requirement would be a minimum of 15 litres per second.

Current thinking (and practice for new build) would require the fan to have a constant 8 l/s trickle and 15 l/s boost.

The fan should have a 15 minute over-run and be operated by the light switch, sensor or humidistat.

100mm fan and duct should be OK for up to 3m and two bends, otherwise consider a 125mm fan and duct.

Siting of the room vent is important - see the manufacturer's guidelines

 

[shd1970]

Thanks woody, appreciated

 

[JohnD]

If you're having a loft-mounted ducted fan, you may as well get a good one.

If you have steamy showers, a throughput of about 240 cu.m/hr will be adequate, with a timed overrun. The better class of fan has a ball-bearing motor and is very quiet. This is much better than the budget fans usually fitted by builders.

This is one of the best, though cheaper brands are available.

4"/100mm In-Line Duct Extractor Fan - 250m3/hr c/w Timer | Soler_&_Palau (5211364500)

The 250 silent with timer would be very suitable.

I favour having it come on automatically with the light switch. As it is very quiet, and economical in electricity, there is no good reason not to.

 

[shd1970]

thanks for the reply @JohnD although at £164 ex vat, its a bit steep in cost

i've been looking on Extractor fan world and they have a Turbo Tube at £76 inc that they offer with a 5 year guarantee with the following credentials so i'm going to give that a shot i think :

Technical Data:
- Max Flow Rate: 300m3/hr
- Max Flow Rate: 83 L/s
- Noise : 24dB(A)
- Watts : 24w

https://www.extractorfanworld.co.uk/turbo-tube-pro-100-4-inch-inline-fan-with-timer-3785-p.asp