Whirlybird Guide – Roof Ventilators and Whirlybirds in Your Home

A guide for the curious consumer interested in Roof Ventilation & Whirlybirds

Without a proper means of insulation or ventilation, a standard roof space quite simply traps & accumulates heat as the sun beats down onto your roof. This heat radiates down through your ceiling, will warm your home, and accounts for around 25% to 35% of the heat gain in summer, right next to windows. Obviously, you can install blinds to block heat out of windows, but you can’t put blinds over your roof.

When roof heat starts seeping through your ceiling, your home becomes stuffy and hot. Most homeowners will resort to using air conditioning, though unventilated roof spaces will continue to transfer heat. Without a means to keep your home cooler for longer, your power & utility bills can skyrocket.

Methods to ventilate your roof have changed drastically over the past couple of decades. The product most readers are familiar with is the roof whirlybird. One of the first designs for the whirlybird was patented in 1910 by Samuel Ewart. This design in principle hasn’t changed in decades, as it still relies on wind to make the turbine spin. They may also rely on the expansion of air in your roof cavity from rising temperatures.

Whirlybird Mechanics – How do they Work?

“Over the last five years I have had two whirlybird units from Bunnings in my ceilings and had, so I thought, done a good job. I later did extensive research and was determined to find an alternative to the whirlybird … The Solar Whiz has now been in for about six months and the temperature difference we have noticed is amazing! On hot days the temperature is about seven degrees cooler upstairs and dramatically cooler downstairs. If I close all the openings in the house and open one window down stairs, I can feel the air being pulled through the window and up the stairs to the top floor.”

Greg Savill (Sydney)

There’s typically two types of whirlybirds: your mechanical, active-powered whirlybird, and the conventional wind-driven whirlybird. The far more popular conventional whirlybird operates when wind hits the turbine fins, causing the vent to rotate. The motion creates a vacuum that sucks air out of the roof space. Unfortunately, a single whirlybird will not usually suffice for a modern home, and may require up to four or six units to be installed to feel an effect!

It is worth noting however that they can assist in reducing heat build-up as well as humidity while enhancing air movement in your home. The design is also typically able to resist rain, though it isn’t impervious.

Whirlybird Cooling and Rate of Airflow – Are they effective?

Depending on what kind of whirlybird manufacturer or model you purchase, each average whirly bird unit is capable of ventilating around 100-150 m³/h in 12 km/h winds individually. Though, naturally, performance will vary from design to design. These factors may range from how warm the air is in your roof space (for air to expand), whirlybird throat size, wind accessibility, to wear & tear in the whirly bird unit itself. Read more about whirly bird models versus other dedicated ventilators here!

In order to feel the effects of ventilation in your home, you might need around 700 m³/h of air flow to keep your roof space near to the ambient temperature outside. Of course, this means you’ll need more than one whirlybird to do the job. 

Whirlybird Cost & Affordability – Is the expense worth it?

A standard whirly bird isn’t terribly expensive. You can pick one up from major hardware stores for as cheap as $60.00 AUD, and sometimes their installation can be done DIY. However, affordability often comes with a compromise in the modern market, as cheaply built whirly birds can present design flaws after installation.

Below is a list of downsides that come with purchasing wind-driven whirly bird turbines for roof ventilation:


  1.  Dependent on Wind Speed.  Whirlybird effectiveness depends on the wind in the area. If there is no wind, it will not operate (except for the rotation created by the air expanding in the roof space as the sun heats it). This becomes a problem during humid, summer days when the wind rarely blows, as well as in areas where wind speeds don’t normally reach 8 kph or more. The only homes that can make the most out of whirlybirds are those situated in windy locations. Otherwise, an air-driven whirlybird is not advisable. Now, the common response to this dilemma is to purchase a powered roof ventilator (mechanical whirlybird) instead. However, powered roof ventilators (whirlybirds) have long lost their appeal to the public as they require an electrician to install and consume energy!
  2. Operate Noisily. Whirlybirds also tend to become noisy due to the rotation of the turbine. As the turbine spins, it rubs on the other parts of the ventilator, thereby causing a low squeaking or grinding noise. The noise gets louder when the wind gets really strong or when the turbine is spinning at an high speed. Additionally, whirlybirds may become noisy once their bearings start to come loose, or when it’s time for their regular lubrication.
  3. Not Very Efficient. Whirlybirds are inexpensive, but not very effective in moving enough air in the roof space in comparison to other roof vents. This is due to the design of whirlybirds, which is rather outdated. As a result, one whirlybird will rarely be able to significantly reduce temperature and humidity levels inside a house. Studies reveal that it would take at least 10-15 residential whirlybirds to effectively cool an average-sized house. Imagine if you have to install 10 whirlybirds for your home. That equates to a minimum of $600, excluding installation fees. Additionally, the noise produced by all 10 whirlybirds can be quite a nuisance for the whole household. An average whirlybird may have a capacity to move around 100 cbm of air per hour (at zero resistance) – whereas powered and solar powered roof ventilators normally start at a capacity of around 1000 cbm/h and goes up to around 3000 cbm/h. Follow this link if you wish to know more about whirlybird flow rates.
  4. Prone to Malfunctioning. While they are specially designed to resist rain, whirlybirds may malfunction once they catch leaves or other debris. If a foreign object enters the vents and interferes with the turbines, the whirlybird’s spinning capacity is decreased. Often, the foreign object only needs to be removed from the turbine (which may not be that easy given the position on the top of the roof). However, in unfortunate cases where the turbine becomes damaged, the whole vent will have to be replaced.

Best Roof Ventilation Alternative: Solar Roof Ventilators

One whirlybird alternative that is worth considering is a solar powered roof ventilator. As its name suggests, solar-powered ventilators or solar roof vents is a type of roof ventilator that relies on solar energy. Since roofs experience an almost constant exposure to the sun, there are no limitations as to where a solar roof fan can be installed.

As long as there is sunlight, solar roof fans can be installed. Additionally, the roof ventilators will work at their best when the sun is directly atop the roof, exactly the time when temperature levels are at their highest.
Another positive thing about solar roof ventilators is that they operate at whisper quiet levels. With their cutting-edge technology, high quality solar roof ventilators like the Solar Whiz roof ventilation unit have whisper quiet operation – even in full sun.

Solar roof ventilation can incorporate a sleeker design which to most people is less obtrusive on roofs than whirlybirds. On top of that, the roof ventilator’s seamless external structure prevents any foreign object from entering. The only disadvantage for solar roof ventilators is the higher unit cost. However let’s be honest, you want something of high quality that is still affordable, not something cheap that doesn’t do the job. Solar roof ventilators often cost up to five times that of whirlybirds Bunnings.

But then again – Solar Roof Ventilators are more efficient and are proven to work 10 to 30 times better and more effectively than traditional whirlybird ventilators. In fact, one solar-powered roof ventilator is normally enough to control the roof space temperature of a home. People actually find that solar roof ventilators are far more cost-effective than whirlybirds in the long run.

solar ventilation install

What about Ventilation for Commercial Properties?

Industrial whirlybirds, on the other hand, with very strong winds operate anywhere from 2,500 to 5,000 m³/h per hour. On average whirly birds need winds of around 8 km/h for a satisfactory performance.

While we provide powerful solar roof ventilation solutions for your home, we also have a commercial ventilation line! We’ve designed them to properly ventilate the extreme heat that large-scale properties can produce. On top of that, our commercial exhaust fans are excellent at adequately ventilating fumes for industrial businesses. Our solar commercial ventilators come in two sizes:

the SW-RAF7000, capable of moving 7,000 m³/h,
and the SW-RAF10000, capable of moving a whopping 10,000 m³/h!

If you’re thinking of buying cheap whirlybirds to help ventilate your business, consider a Solar Whiz instead! You’ll be feeling the difference during those hot summer days.

Conclusion: What is my best roof ventilator option?

Whirlybirds are traditional roof vents that are mainly preferred by customers due to their affordability based on a cost per unit approach, which does not take into consideration the airflow capacity required to effectively ventilate a roof space. Whirlybirds belong to an earlier generation of roof vents and are far surpassed by many high-tech vents today.

When it comes to efficiency, whirlybirds pale in comparison to modern roof vents. Whirlybird performance is also limited as they are wind driven. Modern roof vents may be mains powered or solar powered. Interestingly, solar powered fans available in Australia generally have significantly higher airflow capacity than mains powered roof fans.

To sum it all up, whirlybirds were probably a good roof vent option in the past, however technology has overtaken this design and there are both powered and solar powered alternatives that are both many times more efficient and more cost effective – as you would need a minimum of 10 whirlybirds even on a small house in order to effectively ventilate the roof. Generally the most cost efficient roof ventilation alternative will be a solar powered roof vent, which are easy to install and don’t require an electrician. Solar roof ventilators have 10-30 times the capacity of a whirlybird, like the Windmaster whirlybird– and 2 to 8 times the capacity of popular powered roof vents, like the Edmonds Maestro.

If you want to learn more on the topic of  whirlybird ventilation, or are interested in whirlybird installation onto your Aussie home or warehouse, you can message us on Live Chat or call us on 1300 655 118.