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Topic Title: Bathroom fan woes...
Topic Summary: Two failed fans - what next?
Created On: 30 August 2012 08:21 PM
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 30 August 2012 08:21 PM
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BrucieBonus

Posts: 664
Joined: 20 February 2007

Hi everyone

Just wondered if I could pick your collective brains?

Fitted a new Xpelair 4" timer fan about 18 months ago. It was to replace an existing one (which was not working). This failed after about 10 months. As it was still under warranty, I replaced it with the same unit - this has now failed again. I'm assuming it's the motor as all power is getting to unit OK

What should I be checking???

The ducting length is very short - not even half a meter. The fan is fitted in a ceiling and the ducting goes up, does a 90 degree bend and then out of the wall. The fan is in a shared house, so gets a fair bit of use, but there is an identical one is the second bathroom which is still OK.

Perhaps a move away from Xpelair?

Thoughts much appreciated!

BB
 30 August 2012 08:31 PM
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slittle

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Is there any chance the air is condensating in the short vertical section and running back into the fan ??


Stu
 30 August 2012 08:46 PM
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BrucieBonus

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Stu - didn't think of that. I assumed that the fan duct was so short that this would not be a problem. No moisture when I took a look, but I suppose it could have dried out. The other fan duct is completely vertical (ie up out of a flat roof), but no problem with this one.

Other than fitting a new fan and checking it after having a shower(!) is there any way to tell?
 30 August 2012 09:08 PM
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slittle

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I've seen marks around the fan before where the water has leaked onto the plasterboard.

Also, is the duct horizontial once it goes round the bend. A mate who lives just up the road from me had a duct fan from his shower that packed up. When I went to change it the duct was full of water which had stopped the fan from "pushing" and hence burnt it out.


Stu
 30 August 2012 09:13 PM
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BrucieBonus

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Thanks for quick reply - no marks I could see but I didn't check to see if there was water in the ducting - I'll just need to shove my hand up there!

Many thanks
 30 August 2012 09:37 PM
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mikejumper

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Originally posted by: BrucieBonus
What should I be checking???

Out of interest, did you check the continuity of the windings on the fans that had failed?
Was it a centrifugal or axial fan?
 30 August 2012 10:05 PM
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BrucieBonus

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Hi Mike

No I didn't - is it a case of doing a continuity test on the connecting ends? And if no continuity then it's busted?

It's an axial fan

BB
 30 August 2012 10:45 PM
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peteTLM

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take the circuit board out of the fan, it will have pop marks, grey or black where it has arced over if its condensation.

Also not all fans like being used on the ceiling, it kills the bearings if its not its intended use.

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 31 August 2012 08:54 AM
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OMS

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I think Xpelair only really recommend ducting lengths of just a few times the fan diameter - say max 12" - they also recommend a condensation trap close to the fan - so worth a check in the duct and certainly in the horizontal section - if it falls "back" to the fan it can put a reasonable amount of water back into the fan.

I think the fan is also sold as "universal" fixing - so ceiling mounted shouldn't be a problem

That said, the DX 4" range are pretty bombproof - and I'd check your PO - I'm almost certain they have a 3 year warranty

Regards

OMS

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Failure is always an option
 31 August 2012 09:21 AM
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AJJewsbury

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How airtight is the room? Just a thought that if replacement air can't get in the fan would struggle in the same was as if the outlet was blocked. (OK not likely given the usual level of UK building quality, but maybe worth a quick check - I think the usual rule of thumb is a 10mm gap under the door).
- Andy.
 31 August 2012 09:47 AM
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OMS

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I think the usual rule of thumb is a 10mm gap under the door


LoL - - yes. 10mm undercut will usualy give you all the make up air you need in a bathroom

regards

OMS

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Failure is always an option
 31 August 2012 10:13 AM
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Ricicle

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Originally posted by: AJJewsbury

How airtight is the room? Just a thought that if replacement air can't get in the fan would struggle in the same was as if the outlet was blocked. (OK not likely given the usual level of UK building quality, but maybe worth a quick check - I think the usual rule of thumb is a 10mm gap under the door).

- Andy.


Fans generally have to work harder when they are moving air !

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 31 August 2012 10:50 AM
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OMS

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Fans generally have to work harder when they are moving air !


But volume or mass flow in any system is a function of system resistance

Look at any fan curve and as you increase system resistance the power curve rises for diminishing flow rate (ie an increase in total or static pressure)

Depending on the fan blade arrangement, you can also see significant increase in power with reducing air flow and presure.

Generally, an extract fan in a room with inadequate make up air will draw more current than one with a bigger effective free inlet area - hence undercutting the door.

Regards

OMS

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Failure is always an option
 31 August 2012 12:35 PM
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Ricicle

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Originally posted by: OMS

Fans generally have to work harder when they are moving air !




But volume or mass flow in any system is a function of system resistance



Look at any fan curve and as you increase system resistance the power curve rises for diminishing flow rate (ie an increase in total or static pressure)



Depending on the fan blade arrangement, you can also see significant increase in power with reducing air flow and presure.



Generally, an extract fan in a room with inadequate make up air will draw more current than one with a bigger effective free inlet area - hence undercutting the door.



Regards



OMS


You are probably theoretically correct but in my experience with experimentation (and on the advice of an wise old electrician) when we had overload issues with factory intake/extract fans, closing the ducting dampers a bit reduced the current drawn by the fan motors and it increased when they were opened up again.

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Empty barrels make the most noise.
 31 August 2012 01:08 PM
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OMS

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Well generally closing a damper reduces volume flow by increasing system resistance - ie you move the operating point further back along the fan curve - you may or may not see a decrease in fan power/motor current

Moving that point on the fan performance curve also moves it along the fan power curve - whether you see an increase in fan current or a decrease in fan current will depend on the fan type and where on the curve you happen to be.

try a google for "foward curved and backward curved centrifugal fans" - look for fan flow and power curves

the first will show an increase in power for an increase in volume and an increase in resistance as your experience) the latter will show either increasing or decreasing power consumption for reducing system resistance and increase in air flow - so at low airflow and low resistance the fan has a rising power curve, it swaps over at the other end - so reducing resistance and increasing flow reduce power.

generally, if you run a foward curved centrif "out" of the system (ie at less than design resistance), it really will overload the motor.

Regards

OMS

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 31 August 2012 01:38 PM
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mikejumper

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Originally posted by: BrucieBonus
Hi Mike
No I didn't - is it a case of doing a continuity test on the connecting ends? And if no continuity then it's busted?
BB

You should see several hundred ohms across the motor winding (timer disconnected).
If you get an open circuit then I'd say busted it is.

Also, I think the ducting arrangement probably calls for a centrifugal fan.
 31 August 2012 03:38 PM
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weirdbeard

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Originally posted by: BrucieBonus


Perhaps a move away from Xpelair?




I'd suggest a move away from timer fans in general if possible - in my experience its nearly always the timer pcb that fails, and unless it's what the customer specifically wants I tend towards recommending a manually switched fan.

Although timer fans seem to be the norm these days, a properly selected and installed fan with a manual switch should be sufficient in a lot of instances, for example when taking a shower a decent setup should be able to remove the vast majority of steamy air before it has a chance to condensate on the surroundings, if the fan needs to run on for 10 minutes after a shower it suggests to me that it isn't doing it's job right in the first place!
 31 August 2012 05:04 PM
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AJJewsbury

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Although timer fans seem to be the norm these days, a properly selected and installed fan with a manual switch should be sufficient in a lot of instances, for example when taking a shower a decent setup should be able to remove the vast majority of steamy air before it has a chance to condensate on the surroundings, if the fan needs to run on for 10 minutes after a shower it suggests to me that it isn't doing it's job right in the first place!

Unfortunately building regs seem to demand a 15min over-run for intermittent fans in rooms without an openable window.
- Andy.
 31 August 2012 05:12 PM
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weirdbeard

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Originally posted by: AJJewsbury

Although timer fans seem to be the norm these days, a properly selected and installed fan with a manual switch should be sufficient in a lot of instances, for example when taking a shower a decent setup should be able to remove the vast majority of steamy air before it has a chance to condensate on the surroundings, if the fan needs to run on for 10 minutes after a shower it suggests to me that it isn't doing it's job right in the first place!


Unfortunately building regs seem to demand a 15min over-run for intermittent fans in rooms without an openable window.

- Andy.



Hi Andy, the number of such rooms must be a minority compared to rooms with an openable window, yet I guess the requirement is translated to the one-size-fits-all approach!
 31 August 2012 06:03 PM
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BrucieBonus

Posts: 664
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Hi everyone
Thanks for taking the time to reply

The ducting is pretty short - but if you think a centrifugal fan would be more powerful for 1/2 m of duct then I might give this a go - say something like this
http://www.tlc-direct.co.uk/Products/BGCF100T.html
or even this
http://www.tlc-direct.co.uk/Products/BGCF200T.html
The property is tenanted, so a timer fan is essential - a manual one would not be used
I'm sure the fan is still under warranty, but I want to solve the problem rather than keep having to go back every 9 months (at my cost) to replace it!
I don't think the room is particularly air tight (old property), plus after a shower the door is left open

I'll also check out the windings and possible condensation in the ducting and/or fan

Cheers all

BB
IET » Wiring and the regulations » Bathroom fan woes...

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