On Fri, 23 Jan 2009 09:37:45 -0500, John Grabowski wrote:

wrote in message
...
On 23 Jan, 14:04, "Steve Barker"
wrote:
i'm not sure about your duct sizing, but i'm curious as to why you need to
move so much air AND where is the replacement air coming from?

s

wrote in message

...
I need to extract 247 cubic metres per hour from my bathroom. I will
be using a 150mm ceiling fan capable of extracting 250 m3/ph. Can you
tell me which ducting system I should use for this? I have a 1.5 metre
run. Currently I have 100mm circular flexible hose already installed,
I intend to use a 150mm ¡V 100mm reducing spigot. Do you think this is
sufficient or should I increase the hose diameter, to system 125 for
example?

If I go larger than 100mm hose I will need to use rectangular flexible
hose. It seems that the only rectangular flexible hose options are
options available are ¡§system 125¡¨ (150mm x 70mm) or ¡§System
204¡¨ (204mm x 60mm). System 150 (180mm x 90mm) does not seem to be
available as rectangular flexible hose. Is this correct and what do
you recommend?

Many thanks for you help

I have used a fan size calculator for a bathroom with a power shower
and this the figure it came out with for a room of this size. I am
currently moving 90 cubic meteres an hour and it is not sufficient -
mould, condensation, rust etc . The replacement air is coming from the
hall outside the bathroom.


*If you are ducting the fan outside then you need to have your replacement
air come from outside as well. Otherwise you just create a vacuum and the
exhaust fan does almost nothing. If your fan is ducted to exhaust in the
house then the hall replacement air should suffice. Try opening a window in
another part of the house whenever the exhaust fan is on and see if that
makes a difference. 90 cubic meters is a lot of air. Off hand I would say
that you don't have sufficient replacement air to actually have any
significant flow.

I have NEVER seen a fart fan NOT ducted outside and they never had outside
airflow supply. To do so eliminates heated or air conditioned air in that
room. Instead, the return air should have a filtered fresh air supply.

As far as duct size you should go with the fan manufacturers
recommendations.