Ducts passing through an unheated roof void should
be insulated to minimise condensate formation and must
include a condensation trap and means of running off
condensate. Vertical ducts should be fitted with a condensation
trap and a weather proof cowl of sufficient free area
for the air volume. Horizontal ducts should fall away
from the fan unit.
of Ducting Axial
fans are suitable for use with up to 2 Mts. of ducting
Centrifugal and Mixed Flow fans should be used for ducting
runs longer than 2 Mts.
For maximum performance flexible ducting should be installed
fully extended and try to eliminate sags and
bends and those that remain should have the widest radius
It is difficult to be exact as the air friction for
Soil Pipe, Solid PVC Ducting, Aluminium and PVC ducting
vary considerably as does the back pressure capability
of different fans.
Bends and grilles will also increase performance loss
By increasing the size of duct ( i.e. using 5"
duct with a 4" fan ) will reduce the performance
We recommend you use the largest
duct and fan you can.
Below is an example of the type of
loss you could expect
we have listed details for specific fans on individual
data sheets ( see below )
VALUES WILL BE SIMILAR FOR ALL
MANUFACTURERS OF FANS
and reflect more on the characteristics of ducting than
the performance of the fan
Mixed Flow Fan Output at set distances using Flexible
( mm )
Max Duct Length
Mixed Flow Fan Output at set distances using PVC
( mm )
Max Duct Length
Ventilation units should be placed as high as possible
in the window or wall near any local smells and steam
but not directly above eye level grills, cookers or
direct sources of heat in excess of +40°C.
Do not site in areas containing excessive levels of
grease without suitable filters.
large rooms the extract points should be well and safely
distributed to obtain even ventilation in all areas.
A short circuit of airflow will be avoided by siting
units as far away as practicable from the main source
of air replacement.
Site the fan so that it is accessible for regular periodic
cleaning and servicing. Make sure that grilles, motor
cooling ports and impellers are able to function freely
in accordance with guarantee requirements.
equipment should be isolated before carrying out any
maintenance or cleaning. All fans should be regularly
cleaned and checked, (every month or so, dependent on
usage). Bearings should be oiled where appropriate twice
a year, unless stated otherwise.