If you have a tiled roof the eave vents would be superfluous wouldn t they.
Tiled roof whirlybird.
Also whirlybirds are less effective if you have no sarking under the roof.
Otherwise the whirly bird will just draw air through the gaps in the roof tiles locally and not produce much cross ventilation.
The difference between your 2 whirlybirds could be anything that affects those conditions.
They are also available for download.
This is where the hot air is trapped and installing the whirlybird here allows the hot air to escape and in turn lets the ceiling void to cool down.
If you re a qualified tradesperson you may like to follow these for whirly bird vent installation also.
A closed attic space is needed to force the whirly bird to draw air through the vents.
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Vertically whirlybirds are best situated close to the apex of the roof to capture and expel the maximum volume of rising hot air.
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A whirlybird will work better on a tiled roof as you create a small cross flow.
Air can enter through the tiles and push heat out the whirlybird.
4 they don t work when there is no wind.
One side of your roof is shaded towards the south so doesn t get as hot where the whirlybird is or your roof is a lighter colour than your neighbours so the heat build up is slower etc.
As we all know hot air rises so the whirlybird is installed as close as possible to the ridgeline on your roof.
At this point you ll need to climb into your roof space so that you can mark your exact installation points on the underside of the roof sheets or tiles.
Unlike metal roofs there isn t as much need for eave vents.