Hi All,

We've got a "colony upper" flat in Edinburgh with a converted loft; the
bathroom is upstairs and has a part coombed ceiling. There is currently
a small (4") fan connected to the light circuit; that feeds into
flexible ducting (120mm) which travels laterally for around 2m and then
vents, via a duct-tape-rich bodged joint, into a 3" plastic pipe which
in turn goes up vertically through the roof. The toilet (downstairs)
extractor fan also vents through the same pipe.

We're looking to replace this with an inline fan controlled by a
humidistat and we're looking for a couple of pieces of advice. I think
I may have been a bit enthusiastic in the choice of fan - Manrose 150mm
inline axial, shifts 230m3/hr - although the advice on the ideal size
of fan varies from 3-20 times room volume (about 12m3) per hour. So
that's the first question: how much air do we need to shift (I know
building regs talk about 15l/sec intermittent)? Have I completely
overcooked it with the fan choice? Will it matter much (we're planning
on putting vents in the foot of the door and the inlet will be in the
ceiling)?

Second question is about venting the fan. Ideally, we should either
vent to the eaves from ceiling inlet or mount the fan directly through
the coombe to the roof - neither of these options are possible in our
case (well, the latter one is, but is less desirable). Given that,
we're planning on removing the current outlet and putting in a new one
much closer to the fan itself. Can anyone give us any advice on the
best way of achieving this? Specifically, it seems to be difficult to
get fittings for vents that go up to 150mm diameter.

Cheers - Adam...

Adam-the-Kiwi wrote:

best way of achieving this? Specifically, it seems to be difficult to
get fittings for vents that go up to 150mm diameter.

www.bes.ltd.uk is The Place for all things duct-related - I'm sure
they'll have whatever you need

David

get fittings for vents that go up to 150mm diameter.
www.bes.ltd.uk is The Place for all things duct-related - I'm sure
they'll have whatever you need

Thanks David - will check them out.

Adam-the-Kiwi wrote:
get fittings for vents that go up to 150mm diameter.
www.bes.ltd.uk is The Place for all things duct-related - I'm sure
they'll have whatever you need

Thanks David - will check them out.

Might also want to install a "damper" in your new ducting to prevent
backdraughts
on a windy night.
Search the BES site for "damper" - for round or rectangular channels.

Mungo

Might also want to install a "damper" in your new ducting to prevent
backdraughts
on a windy night.
Search the BES site for "damper" - for round or rectangular channels.

Thanks Mungo - I had already spotted and added to the list. We are
thinking about putting a y-joint in and having the toilet extractor
venting the same way, so I was planning on putting one in on each set
of ducts. Having trouble finding y-connectors, though...

I don't suppose you (or anyone else) has any other thoughts with regard
the OP?

Adam-the-Kiwi wrote:
Might also want to install a "damper" in your new ducting to prevent
backdraughts
on a windy night.
Search the BES site for "damper" - for round or rectangular channels.

Thanks Mungo - I had already spotted and added to the list. We are
thinking about putting a y-joint in and having the toilet extractor
venting the same way, so I was planning on putting one in on each set
of ducts. Having trouble finding y-connectors, though...

Yup. I'd guess you may find trouble getting those. I asked about 15mm Y
copper fittings but no-one knew if these were available (in a recent
different thread).

Regarding the larger-spec fan: my gut feeling is "no". You want to
"cream"
the moist (and/or smelly) air out of the rooms, not apply some inverted
hovercraft.
Too much air movement may create a draught; or it may suck all that
expensive
heated air out your house!
I'd guess that the bigger fan would also be noisier too.

So, sticking with the Building Control requirements on fan size would
be my
(admittedly unscientific) advice.

Mungo