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Frequently Asked Questions
Why is the intake so often the weak point?
It is the half nobody looks at.
Ridge extraction is visible and specified.
The intake is a louvre somebody must remember.
Undersizing it has no obvious culprit.
The whole system underperforms quietly.
It is the commonest gravity fault.
How should intake area relate to extract?
At least matching, and equal performs best.
Air cannot leave faster than it can enter.
The resistances act in series.
Generous ridge area is wasted without intake.
The building behaves as though the ridge were smaller.
Size the two together.
Where should intakes be positioned?
Low, and away from contamination.
Height between intake and outlet drives stack effect.
High intakes reduce that height.
Keep them clear of loading bays and refuse areas.
Vehicle routes and exhaust discharge too.
The building draws in whatever is nearby.
What do louvres and screens cost?
Free area, exactly as elsewhere.
Blades, birdscreens and mesh all reduce it.
Fine insect mesh reduces it substantially.
The screened figure is the design figure.
Nominal opening size overstates it badly.
Compare published free area.
Can intakes be closed in winter?
Yes, with actuated louvres.
That limits heat loss when ventilation is not wanted.
Manual, thermal and motorised versions exist.
Control must coordinate with the extract.
Closing one and not the other achieves little.
Exercise them or they seize.
What if a fan system shares the intake?
The fan's requirement governs the sizing.
It is more demanding than gravity flow.
Undersized intake starves the fan.
That raises fan energy and reduces flow.
Size for the larger of the two duties.
State both when specifying.
What maintenance do they need?
Checking that they are still open.
Screens block with debris and nesting.
Stored goods get stacked against them inside.
That is a very common and invisible blockage.
Inspect from both sides.
Mark the internal clear zone on the floor.