Inline fan under whirlybird

I have seen a youtube video awhile ago about a home owner installing an inline exhaust fan to cool his roof. I was thinking if I could install an inline fan and connect a flexible duct to terminate somewhere just under my whirlybird. The idea is to switch it on very hot days. I do not care about wearing out the whirlybird's bearings as I can always replace it with a better one later. I can get an electrician to install a 3-pin socket near where I want to install the inline fan with a wall switch inside the house. Wondering if my idea makes sense?

This sounds redundant. Where would the ducting be drawing hot air from?

Good question, have not thought about that. I have air vents under eaves if that makes a difference.

the fundamental principles that the whirly bird works on doesn't require additional air to be directed to it for it to work. Adding fans or ducts to direct more towards it I would imagine would do sweet FA. You would get more value from installing a second and even a third whirly bird if you feel the roof space isn't getting the ventilation it needs.

We installed a whirlybird over the exhaust fan in a rental property bathroom. We did this not for removing heat but moist air. The bathroom originally had no exhaust The ceiling cavity was very small and the bathroom had a mould issue.

This appears to have worked well for the mould issue but as far as cooling down the house i would be very surprised if it helped at all.

those are there so that the colder air comes in via the eaves, while the WB sucks the hot air out.

tbh you'd be better off either putting more WBs on, and/or swapping/topping up the ceiling insulation to a higher R value.