• Free Air: 30cm²
• Core drill ‘Black Hole' ventilator BM725
• Rated Input - Max 13kW (44,000 Btu/h)
• Size: 127mm (5") diameter
• ‘Black Hole' cavity liner and extension piece.
• Tube length from 228mm to 585mm with extension tube supplied.
• Brown outer cowl white inner grille.
• Fixed anti-draught baffles.

The BLACK HOLE Ventilation range

‘Black Hole' ventilation products provide the
answer to the dangerous practice of
ventilators being blocked off by occupiers who
are being annoyed by draughts. This makes an
important contribution to safety. New tests
show that while this works the ventilator may
not pass the required amount of air when the
appliance is operating.
THEREFORE IT IS IMPORTANT THAT A
SPILLAGE TEST IS CARRIED OUT AS
REQUIRED BY THE BRITISH STANDARD
AND CORGI GOOD PRACTICE
The benefits of a ‘Black Hole'
The ‘Black Hole' magic explained
As outside wind pressure increases, a normal
ventilator lets more air through causing
annoying draughts.
Inside the Stadium ‘Black Hole' Ventilator
vortices are formed behind the internal
blades as the incoming air is forced to change
direction. The gap that the air is able to pass
through narrows. As wind pressure increases,
the vortices grow, so reducing the total air
flow, finally tumbling and slowing to a trickle,
thereby cutting down annoying draughts.
Stops wind blasting in - the air flow within
the duct is slowed down by the change of
direction and by the vortices formed,
reducing draughts to a minimum.
Stops light showing through - the
occupier cannot see through the ventilator
and is less likely to be worried that insects
and vermin may enter the house through it.
Stops light shining out - night flying insects
like moths, crane flies and mosquitoes are
not attracted in.
Absorbs outside noise - reduces the
penetration of traffic noise. The internal
construction works as a sound baffle.
Allows air to be pulled through by the
appliance when it is operating.
Safety - with draught and light annoyance
problems eliminated, the occupier will not
be tempted to block off the vent.
However, when the heating appliance is
operating, air is drawn through the vent and
actually speeds up within the constricted air
flow between the vortices, thus maintaining
the correct amount of air into the room or
compartment to allow the fuel to burn
efficiently and flue gases to escape.
When the appliance is not working, incoming
air is reduced to a minimum, even on windy
days. The actual physical difference is that of
air blown or drawn. The energy of the blown
air (wind) is quickly dissipated by the
restriction of the internal shape and the
vortices, while the drawn air will flow
smoothly round the vortices.
BS 5440 Part 2, 2000:
Several changes have been made to update
the previous ventilation standard. Three of
the main ones are summed up below but as
with all new standards they are not
retrospective.
1. The previous words ‘Free Air Space' are
replaced by ‘Free Area' measured and
Effective ‘Free Area' (see point 3).
2. The ‘Free Area' requirement has been
increased from 4.5cm2 to 5cm2 per kW above
7kW input rating.
3. Complex and anti-draught ventilators shall
be measured by the volume of air that they
will pass i.e. the ‘EFFECTIVE FREE AREA' .
The ventilator should be marked accordingly.