Curiousity - Bathroom Fans

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Just out of curiosity, are 12V timer fans noisier than 240V fans....?
I got a 12V fan and my neighbour nearly jumps out of her skin when it is switched on.
I installed it correctly a few months ago but after a week I disconnected it.
It must be bad though because I can hear it downstairs through 3 closed doors.
The fan is from Screwfix....
James
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the_constructor wrote:

Check out the rotational speed. For a given airflow, the DC fan solution of a higher rotational speed is cheaper than the ac fan solution of redesigned fan blades. Unfortunately, it tends to also be a noisier solution. DC fans tend to have higher starting torques, so the onset of the noise is much more sudden, too.
One of the advantages of DC fans is that it is usually very easy to decrease the fan speed and hence greatly reduce the noise. Simply by lowering the DC voltage. Even a small reduction in voltage (eg a couple of diodes in series with the supply) can make a great difference.
--
Sue

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On 2008-02-24 12:09:36 +0000, "the_constructor"

It depends.
There are several factors:
- Fan size. A larger one under-run will be much quieter than a small one run at max setting
- axial/centrifugal. Centrifugal fans can have more throughput and are able to move air through a long duct better than axial fans. However, they are noisier.
- bearings and motor. This relates to the manufacturer and quality of the product.
- mounting. A fan mounted directly to a plasterboard wall or especially ceiling has a very good sounding board to amplify the sound.

Mmmm.....
Take a look at the LoWatt range from Vent Axia. I fitted one of these in my cloakroom. It is suitable for bathrooms as well and runs from 12v. Very quiet indeed. I fitted it using rubber mounts and sealing gasket, which reduces the sound yet further.
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My experience of a few makes:
Manrose: Sleeve bearings, cease, motor burns out.
Deta: Sleeve bearings, cease, self-reseting thermal trip protects motor, thus repairable. (Don't think Deta exist any more. CPC used to do their range.)
Vent-axia: Haven't had one go wrong yet, so I haven't had to look inside. Noisey (might be ball bearing -- they are not as quiet as sleeve bearings).
--
Andrew Gabriel
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Can you possibly give me a ref number please ? Can you explain difference between axial and centrifugal etc. James
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On 2008-02-27 23:19:32 +0000, "the_constructor"

http://www.vent-axia.com/lo-carbon/locarbon-residential.asp
http://www.vent-axia.com/knowledge/handbook/section1/whatisafan.asp
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the_constructor wrote: <snip>

Axial - think boat propeller. Air comes in the front and goes out the back.
http://www.bobstevenson.co.uk/images/turngrove_axial_fan.jpg
Where this type comes into its own is when the flow needs to be capable of being reversed.
Centrifugal - think spin drier. Air comes in at the centre and leaves at the edge.
http://img.alibaba.com/photo/50549687/Centrifugal_Fan_with_Forward_Curved_Blades.jpg
Where this type comes into its own is when operating against back pressure, eg a long delivery tube or trunking.
--
Sue



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Try this as well:
http://www.engineeringtoolbox.com/fan-types-d_142.html
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Hi, I would like to thank everyone for their input on this subject. I am really grateful for all your help. James
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A 12V fan by manufacturer A maybe a lot quiter than a 240V fan made by manufactuer B. Quality counts. Greenwood and Vent Axia are good makes.

Is it an inline fan mounted onto a joist? You need to isolate the fan from the joist with rubber to make it quieter.

That is bad.
Adam
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the_constructor wrote:

[...]
I have one of each type at home in the two bathrooms, both cheapo Screwfix in-line ones mounted on rafters or joists. If anything, I'd say the 240V one was a bit noisier; may be down to less effective mounting (the 12V one's definitely mounted on rubber pads but I can't remember how I did the 240V one!)
David
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the_constructor wrote:

12v fans are exactly the ones fitted in PCs. If you want quiet, look at someone like quietpc.com and find a low noise case fan. Make sure it isn't speed regulated though, you want a 2-wire one, and replace the one in the unit.
A word of caution - some quiet fans are quiet just because they don't push much air. And the one in the unit you've bought may be a high power centrifugal unit, much better at pushing air through a duct against an incoming wind!
I've had a case fan in a vent unit for the last 15 years or so. It's getting a bit tired now!
Andy
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I only ever looked at one, a Wickes one, about 5 years ago. That was a shaded pole induction motor, exactly the same as the mains ones (but presumably thicker wire in the windings), and fed via a separate 12VAC transformer. Quite different from PC fans, which run from DC.
--
Andrew Gabriel
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Andrew Gabriel wrote:

:O
I stand corrected. My fan BTW is a mains one... and when did you last see a mains case fan?
Andy
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This morning, at the Tolworth computer fair. Several stands at the Bracknell computer fair have been regularly selling them for a couple of years now.
--
Andrew Gabriel
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Andrew Gabriel wrote:

I'm not doing very well here am I!
Andy
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I have a screwfix ceiling mounted bathroom fan that plugs into a 4ins duct which extracts through the pine end of the bungalow. In order to reduce the awful noise it generates, I have been looking for an externally mounted fan which would, I believe reduce the noise level. I have failed to find a fan in the UK but have found an American one which would do the business if I could find an European or better still a British agent which could supply a 240V model. I have a link to the Fan as follows: http://www.continentalfan.com/ext
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Sorry, the link in the first message is wrong, I left out the htm at the end. The correct link is in the second message i.e.
http://www.continentalfan.com/ext.htm
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