Roof Ventilation or Whirly Birds - Do They Work?

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Re: Roof Ventilation or Whirly Birds - Do They Work?

Postby AWDFun » Tue Nov 20, 2012 12:57 pm

Bringing up an old thread but I have 4 of these Twista 400mm units on my single storey house.

Does it work? yes it does. Last summer we had them installed midway through summer as we were turning on the ducted almost everyday. Since we had the 4 installed even my wife agreed that theres a noticible difference and we hardly turned on our ducted for the rest of the summer.

Before I had them installed I was in the roof area often running network cables and home theatre speaker cables in the roof down the walls, I would literally be dripping sweat even with the few tiles removed for lighting. Since having these however I am up and down the roof with easy and can spent a considerable amount of time in the roof now.

I can definately feel air pressure ( cool air ) being sucked up from the manhole, from within the house not the garage so there has to be some sort of pressure to suck up that much air. If I am near the manhole when Im working up there I take the extra few steps to put my face over the manhole and get a gush of cool air on my face.

I havent got any under eaves vents installed yet, they are sitting in the shed waiting for when Im not lazy to install them but the amount of sunlight I get through the tiles suggests to me that theres enough air flow through the tiles to have some effect as the fan/fins in the Twista when it turns.

Im considering to purchase a $99 Bunnings special 300mm whirlybird with no fan/fins and also mounting a 300mm radiator fan under it as the previous poster. Shall be connected to a 12V battery and recharged via solar.
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Re: Roof Ventilation or Whirly Birds - Do They Work?

Postby bpratt » Thu Dec 26, 2013 9:14 pm

Came across the Broan brand at a Masters store the other day, and thought I'd resurrect this thread in case anyone was still watching. :)

$249 for a solar powered fan that moves 650CMH seems to be quite a reasonable deal.

http://www.masters.com.au/product/90005 ... ilator.jsp

http://www.broan.com.au/products/filter ... 7d8db82f51


Anyone seen or used these before? how did they stack up for you ?
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Re: Roof Ventilation or Whirly Birds - Do They Work?

Postby james22442 » Thu Feb 13, 2014 8:55 am

[Moderator- posting removed, merchant posing as a consumer]
Last edited by Gordon-Loomberah on Wed Feb 19, 2014 10:30 am, edited 2 times in total.
Reason: removed excessive quoting - entire previous posting
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Re: Roof Ventilation or Whirly Birds - Do They Work?

Postby bpratt » Mon Feb 17, 2014 7:32 pm

Thanks for the info on those ones. I was of the ideal that they were useful for either tiled or colourbond roofs, but it seems like they'll have a very limited market in Australia, which will probably mean Masters and the like will see with returns and non-sales, that solar powered ventilation is a product that they should not ever carry in stock.


I also saw a different brand at Mitre 10 a couple of weeks ago, and seem to be fairly similar, in fact this time they show a picture with it on a corrogated roof.

http://shop.mitre10.com.au/solafan-sola ... -roof.html
Kaco 6600
26 x Trina Honey 250w panels. (wish I could work out how to upload to pvoutput.org)

New house build :-
http://bandlnewhomebuild.blogspot.com

My weather station :-
http://jimboombaweather.com
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Re: Roof Ventilation or Whirly Birds - Do They Work?

Postby james22442 » Tue Feb 18, 2014 9:20 am

[Moderator- posting removed, merchant posing as a consumer]
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Re: Roof Ventilation or Whirly Birds - Do They Work?

Postby ilmessaggio » Sat Jul 29, 2017 5:10 pm

Roof Ventilators Explained

Let's start off with the so called wind driven Whirly, Whizbanger, Spinner, generic rotary ventilator fabricated in aluminium. Some rotate on bushes, some rotate on plastic bearings, some rotate on steel bearings.....and either way they are going to rotate easily because there is little mass (weight) to them.

The function of this type of roof ventilator is to create a negative pressure in the roof by drawing out a volume of air proportional to the rotating speed of the rotor (the spinning part)

In order for the rotor to be effective, the distance between the rotor and the spigot cannot be any more than 3mm. If it's greater then the air that would normally be drawn up from the roof by the rotor is going to be short circuited and drawn in through the gap between rotor and spigot, thereby nullifying the potential of the rotor.

So there you are in the hardware store, you spin the rotor of the roof ventilator forgetting that the potential of what you are looking at is in reality half because half the surface area has got pressure against it and air can only escape from the other half on the opposite side.

The best rotary ventilator in Australia was the Western Rotary which was made in steel, rotated on lubricated bushes and could suck like a hungry goat. This unit was last seen some 35 years ago and replaced by the inefficient product as seen today.

Then we have the pressure responsive roof ventilator which is made and sold under many names and referred to as a 'passive', 'static', and anything that implied that it was less dynamic than the zip zap whizbanger whereas in fact operates far more consistently than it's 'active' cousins.

The performance of this type of roof ventilator is governed by heat and pressure and the flow rate is proportional to the 'free air' area of the ventilator. Now the roof ventilator size may be a x c in size but the flow potential may well be 1/3 of that, and just like it's cousin, it's efficiency is governed by side opposite the pressure face.

The variations encountered by this type of roof ventilator are far greater and what makes them more attractive to the architect and homeowner alike is their benign appearance.


Then last but not least you have the Cupola style, as seen on many a gracious residence.
This type of roof ventilator was the precursor to those seen today although the presence of the Cupola design is quite distinctive and regarded as the finer touch on the 'crown' of the residence.

Today the Cupola is used as a services hub to where all exhaust ducting is terminated as well as performing the task of venting the roof and keeping the dwelling cool.

Usually mounted centrally and straddled across two or more planes on the roof although appears more functional than ornate as those of the past historical roofs in architecture
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