Extractor fans not much good...

[garmcqui]

Hi all,

We just moved into a new build in August, and over this time I've noticed the bathroom extractor fans don't do much of a job of getting rid of condensation - the mirrors etc are still steamed up an hour after a shower etc.

The builders have fitted a Nuaire "Genie X" fan in the ceilings of all bathrooms (2 of which have no windows), utility room (no window) and the kitchen:

Now the specs for this fan list the following airflow (mine are surface mounted, unfortunately):

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• garmcqui
• 15 Nov 2014
• 1

Which doesn't seem like much, especially in comparison to what's out there.

Now, I found these Part F building regs online:

a - Bathroom - 15 litres / second
b - Kitchen - 60 litres / second
c - Utility Room - 30 litres / second

and these Nuaire Genie fans just about seem to match the Bathroom requirements, but not the utility room or kitchen requirements.

Are there much better fans out there, and should I be querying their fitment with the builders?

Thanks

 

[OwainDIYer]

have you checked the fan actually vents to the outside? How long is the duct?

 

[JohnD]

and how long does the extractor run? (the door should be closed)

Do you have access to the space above the ceiling?

 

[garmcqui]

fan definitely vents to the outside, through vents in the roof. The ducting isn't overly long, this is the arrangement in the attic from above the two upstairs bathrooms:

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• garmcqui
• 15 Nov 2014
• 1

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• garmcqui
• 15 Nov 2014
• 1

The extractors are strange - they're on all the time, yet at a vastly reduced speed (almost inaudible), then they come on full power with the room light, then go back to background speed as soon as the light is switched off. Nuaire call it "Continuous Trickle Extractor with Switched Boost".

I've had a look and there's no adjustment for over-run etc.

 

[JohnD]

that's great. You can chuck them away and install a ducted inline fan with overrun timer, which will have about three times the max power of those things (typically 240 cu.m/hr). They are quieter than ordinary extractors.

btw you need to flop insulation over those ducts, or they will get condensation inside and drip into the fans.

 

[garmcqui]

cheers, any recommendations John?

Should I be pulling the builder up about the fans fitted in kitchen/utility room not being up to spec? (can't imagine these fans are doing much more than 15L/sec (54m3/hr).

Regarding insulation, the ducts seem to be double walled, with fibreglass-type insulation between...

 

[JohnD]

this sort of thing
http://www.screwfix.com/search?search=inline+fan

The Vent-Axia seems to have better reviews than Expelair

Manrose may be cheaper, and I have seen unbranded ones on ebay. but look at the extract rate, some of them are low power, also look at the noise rating in db

http://www.tlc-direct.co.uk/Main_Index/Ventilation_Index/4_Inch_Fans_Duct/index.html

Your access is so good that it would not be difficult to swap new for old, if you buy a cheap one and it doesn't last.

I would definitely start with the bathroom, because of the risk of condensation damp and mould.

Fit it on a ply board, padded top and bottom surfaces with rubber or synthetic (not wool) carpet or underlay

 

[garmcqui]

That's great, thanks for the advice John.

I've seen this one being raved about elsewhere... Manrose MF100T (245m3/hr)

http://www.amazon.co.uk/MANROSE-MF100T-IN-LINE-EXTRACTOR-MIXEDFLOW/dp/B005F41YOM

 

[ricicle]

btw you need to flop insulation over those ducts, or they will get condensation inside and drip into the fans.

That already looks to be insulated ducting !

 

[ban-all-sheds]

The ducting isn't overly long

Well - whether it is "overly" long or not is debatable.
What is not debatable though is that the performance figures you see for fans all assume no ducting at all. And several m of flexible ducting will halve the performance of a typical 100-125mm fan.

I would be wary of following JohnD's advice - you've got a new-build house, so it will be very air tight. You need a system of continuous mechanical ventilation (ideally with heat recovery) or you'll start to get condensation/damp/mould problems throughout the house. Each person there exhales water vapour in quantities measured in litres per day. Pets add more. Baths, showers, cooking, laundry and cleaning add more. Houseplants add more. Coming in from outside with wet shoes and coats adds more.

I can well believe that the builders installed a poxy system which doesn't work very well, but rather than replace it with a traditional timed-overrun fan I would advise getting a competent HVAC firm to discuss options for a proper continuous mechanical ventilation system.