Hi All,

We have a flat with a toilet (pretty much literally a WC - just a room
with toilet and small handbasin - a little less than 2.5m3) bang in
the middle of the building (it's a "colony upper" in Edinburgh for
those familiar with them). That means that it is, give or take, 5-6m
from the outside in any direction. The path that we are proposing for
the extractor ducting involves going upwards from the (false) ceiling
for about a metre into a shared loft space, then around 5m
horizontally to a vent in the roof (already installed). Was planning
to have an axial fan in line at the outside vent end - axial because
the loft space there is right next to our neighbour's bedroom and I
thought a centrifugal fan might be too noisy.

Questions:
- I was planning on using 4" circular section ducting for the 1m rise,
then the box-section ducting for the horizontal run. Any problems with
that plan?
- There are a couple of oblique angles - what is the best way to
achieve these?
- We may have to navigate the ducting round some very old piping.
Obviously, we'll try to minimise curvature, but is there an
alternative to the bellows-type ducting for this?
- Am I being hopelessly optimistic in using a 4" axial fan to drive
this?

Any other advice or experience will be gratefully received!

Thanks - Adam...

On 2007-11-03 11:27:22 +0000, Adam-the-Kiwi said:

Hi All,

We have a flat with a toilet (pretty much literally a WC - just a room
with toilet and small handbasin - a little less than 2.5m3) bang in
the middle of the building (it's a "colony upper" in Edinburgh for
those familiar with them). That means that it is, give or take, 5-6m
from the outside in any direction. The path that we are proposing for
the extractor ducting involves going upwards from the (false) ceiling
for about a metre into a shared loft space, then around 5m
horizontally to a vent in the roof (already installed). Was planning
to have an axial fan in line at the outside vent end - axial because
the loft space there is right next to our neighbour's bedroom and I
thought a centrifugal fan might be too noisy.

Questions:
- I was planning on using 4" circular section ducting for the 1m rise,
then the box-section ducting for the horizontal run. Any problems with
that plan?

Over this distance, that's going to add up to a lot of air resistance.



- There are a couple of oblique angles - what is the best way to
achieve these?
- We may have to navigate the ducting round some very old piping.
Obviously, we'll try to minimise curvature, but is there an
alternative to the bellows-type ducting for this?

Yes. A better solution would be to get a length of air conditioning
flexible ducting for the whole run. You can get it with an almost
smooth internal surface. If you think that there might be
condensation (shouldn't be from this room but possible others?) , then
there is an insulated version as well.

Go for a 150mm duct rather than 100mm and that will reduce air
resistance considerably. You can get size adaptors.



- Am I being hopelessly optimistic in using a 4" axial fan to drive
this?

With what you were proposing, yes. The general recommendation is up to
about 3m for a typical axial 100mm fan. A 100mm centrifugal fan
would be OK on a reasonable duct, or you could go up to a 150mm axial
fan with a speed controller and that would be very quiet.

Have a look on the Vent Axia site for good design information and good
products.



Any other advice or experience will be gratefully received!

Thanks - Adam...

Andy Hall wrote:
On 2007-11-03 11:27:22 +0000, Adam-the-Kiwi
said:

Hi All,

We have a flat with a toilet (pretty much literally a WC - just a room
with toilet and small handbasin - a little less than 2.5m3) bang in
the middle of the building (it's a "colony upper" in Edinburgh for
those familiar with them). That means that it is, give or take, 5-6m
from the outside in any direction. The path that we are proposing for
the extractor ducting involves going upwards from the (false) ceiling
for about a metre into a shared loft space, then around 5m
horizontally to a vent in the roof (already installed). Was planning
to have an axial fan in line at the outside vent end - axial because
the loft space there is right next to our neighbour's bedroom and I
thought a centrifugal fan might be too noisy.

Questions:
- I was planning on using 4" circular section ducting for the 1m rise,
then the box-section ducting for the horizontal run. Any problems with
that plan?

Over this distance, that's going to add up to a lot of air resistance.



- There are a couple of oblique angles - what is the best way to
achieve these?
- We may have to navigate the ducting round some very old piping.
Obviously, we'll try to minimise curvature, but is there an
alternative to the bellows-type ducting for this?

Yes. A better solution would be to get a length of air conditioning
flexible ducting for the whole run. You can get it with an almost
smooth internal surface. If you think that there might be
condensation (shouldn't be from this room but possible others?) , then
there is an insulated version as well.

Go for a 150mm duct rather than 100mm and that will reduce air
resistance considerably. You can get size adaptors.



- Am I being hopelessly optimistic in using a 4" axial fan to drive
this?

With what you were proposing, yes. The general recommendation is up to
about 3m for a typical axial 100mm fan. A 100mm centrifugal fan would
be OK on a reasonable duct, or you could go up to a 150mm axial fan with
a speed controller and that would be very quiet.

Have a look on the Vent Axia site for good design information and good
products.



Any other advice or experience will be gratefully received!

Thanks - Adam...




Totally agree with the above, and will add one thing to the mix.

Mount whatever fan you use on some rubber or foam rubber blocks. And at
least have flexible pipe on that section, and throw a bit of rockwool
over it. All in the interest of noise. Wrapping some lead round it may
help also, and boxing it in.

On 3 Nov, 11:46, Andy Hall wrote:
On 2007-11-03 11:27:22 +0000, Adam-the-Kiwi said:
We have a flat with a toilet (pretty much literally a WC - just a room
with toilet and small handbasin - a little less than 2.5m3) bang in
the middle of the building (it's a "colony upper" in Edinburgh for
those familiar with them). That means that it is, give or take, 5-6m
from the outside in any direction. The path that we are proposing for
the extractor ducting involves going upwards from the (false) ceiling
for about a metre into a shared loft space, then around 5m
horizontally to a vent in the roof (already installed). Was planning
to have an axial fan in line at the outside vent end - axial because
the loft space there is right next to our neighbour's bedroom and I
thought a centrifugal fan might be too noisy.

Questions:
- I was planning on using 4" circular section ducting for the 1m rise,
then the box-section ducting for the horizontal run. Any problems with
that plan?

Over this distance, that's going to add up to a lot of air resistance.

- There are a couple of oblique angles - what is the best way to
achieve these?
- We may have to navigate the ducting round some very old piping.
Obviously, we'll try to minimise curvature, but is there an
alternative to the bellows-type ducting for this?

Yes. A better solution would be to get a length of air conditioning
flexible ducting for the whole run. You can get it with an almost
smooth internal surface. If you think that there might be
condensation (shouldn't be from this room but possible others?) , then
there is an insulated version as well.

Andy, thanks for the info. I haven't yet been able to find any on the
Vent Axia site. I'll keep looking, but can you give me any specific
products or suppliers?

Go for a 150mm duct rather than 100mm and that will reduce air
resistance considerably. You can get size adaptors.

- Am I being hopelessly optimistic in using a 4" axial fan to drive
this?

With what you were proposing, yes. The general recommendation is up to
about 3m for a typical axial 100mm fan. A 100mm centrifugal fan
would be OK on a reasonable duct, or you could go up to a 150mm axial
fan with a speed controller and that would be very quiet.

Have a look on the Vent Axia site for good design information and good
products.

Thanks for the help - Adam...

On 2007-11-03 14:26:53 +0000, Adam-the-Kiwi said:

Andy, thanks for the info. I haven't yet been able to find any on the
Vent Axia site. I'll keep looking, but can you give me any specific
products or suppliers?

Go for a 150mm duct rather than 100mm and that will reduce air
resistance considerably. You can get size adaptors.

- Am I being hopelessly optimistic in using a 4" axial fan to drive
this?

With what you were proposing, yes. The general recommendation is up to
about 3m for a typical axial 100mm fan. A 100mm centrifugal fan
would be OK on a reasonable duct, or you could go up to a 150mm axial
fan with a speed controller and that would be very quiet.

Have a look on the Vent Axia site for good design information and good
products.

Thanks for the help - Adam...

Do a search in Google using keywords 'insulated ducting' and you will
see loads of suppliers.