Worth installing 150mm fan with only 100mm ducting?

Lobster

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Feb 15, 2014, 2:13:39 PM2/15/14

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I've got a 100mm inline extractor fan in the ensuite; there's a vent in the
ceiling and it ducts the air up into the roofspace (in corrugated flexible
ducting) and as this is a dormer-style house with a very low roofline, it
passes down under the tiles in 100mm rigid flat ducting to a grille just
below the guttering.

It's really very ineffective though, and while I'm scrabbling around in the
roof space sorting out my downlighter wiring I thought I might try fixing
this too... I was considering replacing the 100mm fan with a 150mm model;
however, realistically there's no easy way to upgrade the length of fixed
100mm ducting (about 1-1.5m worth) which runs under the roof tiles. I
would replace the flexible stuff in the roof space with 150mm ducting,
probably rigid rather than the flexible hose.

Question is, would that be worthwhile at all? Would the old 100mm section,
which I can't upgrade, just act as a bottleneck to eliminate any benefit?

Thanks

--
David

gremlin_95

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Feb 15, 2014, 4:37:29 PM2/15/14

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Have you considered a mixed flow fan? They can deliver a good flow rate
under high resistance. I have a 100mm Vent Axia one which has about a
metre of flexible ductwork on each side and it vents out through a
dedicated roof vent tile. It works extremely well, the roof tile creates
a lot of resistance due to its design but the fan is still able to
deliver a decent flow rate.

http://www.vent-axia.com/product/acm-line-mixed-flow-fans-acm100.html

--
Dawood

bert

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Feb 15, 2014, 4:33:22 PM2/15/14

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In message <XnsA2D5C39C7C242d...@81.171.92.236>, Lobster
<davidlobs...@hotmail.com> writes

Monrose do a high powered 100mm fan.
--
bert

PeterC

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Feb 15, 2014, 4:57:05 PM2/15/14

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Rigid would, in itself, help, as corrugations cause a lot of drag.
--
Peter.
The gods will stay away
whilst religions hold sway

DerbyBorn

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Feb 15, 2014, 6:12:04 PM2/15/14

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PeterC <giraffe...@homecall.co.uk> wrote in
news:1rkmniph29z45.1...@40tude.net:

Corrugations also allow a build up of fluff.

What is meant by "mixed flow"?

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DerbyBorn

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gremlin_95

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Feb 15, 2014, 6:13:58 PM2/15/14

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"In a mixed flow fan the air flows in both axial and radial direction
relative to the shaft. Mixed flow fans develops higher pressures than
axial fans."

Read more: http://www.engineeringtoolbox.com/fan-types-d_142.html
--
Dawood

Capitol

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Feb 15, 2014, 6:36:56 PM2/15/14

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Is the fan the right way round? Yes, I know it's a stupid question!

harryagain

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Feb 16, 2014, 4:11:03 AM2/16/14

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"Lobster" <davidlobs...@hotmail.com> wrote in message
news:XnsA2D5C39C7C242d...@81.171.92.236...

There are two aspects to fans, the volume they shift and the pressure they
develop.
(As with all bladed pumps, centrifugal and axial)
It sounds like your fan does not develop enough pressure.

There are special high pressure fans for long ducts, usually centrifugal.

Brian Gaff

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Feb 16, 2014, 4:36:44 AM2/16/14

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Assuming you can join them in a sloping kind of way, it will work, is all i
can say, as I've seen this sort ogf thing done via a reducer. I guess it
depends on how much 'oomph' the fan can deliver!
Brian

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"Lobster" <davidlobs...@hotmail.com> wrote in message
news:XnsA2D5C39C7C242d...@81.171.92.236...

Chris J Dixon

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Feb 16, 2014, 6:34:07 AM2/16/14

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After recommendation here, I bought one of these:
http://www.tlc-direct.co.uk/Products/SLTD350SILENTslashT.html

Admittedly not cheap, but I was amazed by how quiet it was, I had
to feel the air to be sure it was running. The airflow is far
better than the (failed) cheap one it replaced. It can push-fit
into the pipework, and is readily removable for cleaning.

Chris
--
Chris J Dixon Nottingham UK
ch...@cdixon.me.uk

Plant amazing Acers.

Lobster

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Feb 16, 2014, 7:03:58 AM2/16/14

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On 16 Feb 2014, "harryagain" <harry...@btinternet.com> grunted:

Yeah, I think the answer is maybe just to replace it with a 100mm
centrifugal model.

The plot thickens actually: the 150mm fan I was originally thinking of
going for was http://tinyurl.com/ma4xp3c (or
http://www.toolstation.com/shop/Electrical/Fans/150mm%20Part%20L%
20Inline
%20Shower%20Fan%20Kit%20with%20Timer/d190/sd280/p97314); however I
hadn't originally spotted that this doesn't coincide with the standard
ducting sizes which are 100mm or 125mm. Weird!

--
David

sm_jamieson

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Feb 17, 2014, 4:21:41 AM2/17/14

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+1
Excellent fans, very quiet. That is until you control them with a triac controller, but that is a matter for the other post !
Simon.