• 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.