Whirlybirds vs Solar Whirlybirds vs Power Exhausts

There are two or three topics on insulation; this is not about insulation although related, so I am starting a new topic.

Has anyone upgraded or installed solar whirlybirds or mains powered exhausts, and what have been your experiences? There are lots of references to whirlybirds but not many to solar or mains powered ones beyond ads and the odd whirlpool discussion.

I found one ‘throw away’ reference on the community but not so many details were included.

My 2 whirlybird house in NE Melbourne has heat build up in the roof cavity in summer and gets cold in winter so I am considering addressing this because one of the whirlybirds is signalling it needs attention at 22 years.

There are ceiling batts and insulation under the colourbond. A reasonable expectation is either a solar whirlybird or powered exhaust will improve comfort by cooling the roof cavity in summer and letting it get a bit warmer in winter.

Adverts for thermostatically controlled solar whirlybirds w/onboard batteries include lots of puffery as well as believable claims, roughly $400~500 per typical unit plus installation. Thermostatically controlled mains powered exhausts seem to be about double plus added sparky costs (PV system notwithstanding) leading me to think the solar variety are the ‘gold standard’ for price-performance.


I periodically read the posts in whirlpool.net.au, there are many and varied opinions about which is best, including some which say dont bother with any. I’m none the wiser and I still don’t have one installed in spite of requesting a quote via the Edmonds site…4 years ago…

You could peruse some of these threads


Thanks for that @SueW, your link led to a few topic I missed there.

That there are, a difference here is I ‘know’ some of our members who have experience in many relevant things, as well as my personal trust in their opinions.


We need our roof redone, and have to start looking into these devices.

Some years ago, I heard about unpowered thermostatic ones which open when hot, and stop working when cold. Are they still around, and are they different to the ones you mentioned @PhilT?


That was the type we had in the NT and Isa. Worked well for us and helped keep the ceiling cooler (we also had insulation batts). Can’t remember the brand as it was many years ago, and I can’t say if they exist anymore. I think the Solar ones seem a good option these days eg Solar Star RM1200 or RM1600 or the Solar Whiz range https://www.solarwhiz.com.au/products-page/.


I have not seen ones that just open and close.

Thanks for the reply and recommendation :slight_smile:


I only have the old style on this house, they work well but you need a few (we have 8). After looking at the solar options and only needing 1 or possibly 2 for our roof area I think I would now spend on the solar versions, and while it might be a bit more than the old style it seems a better outcome particularly with thermo control.

Old style each remove about 100m3/hr or a small bit more (at best) depending on wind speed and they need somewhere around 8 km/h wind speed to start operating properly (beyond hot air expanding in the roof). It is also very important to have vents to allow airflow into the roof cavity, under the eaves. Lots of people forget to add these vents and wonder why they don’t get the results they expected. These vents would also be important for the powered types of whirlys.


Sorry; my wording was vague. To clarify, they still whirl around whether open or closed. It is the ‘throat’ that opens at the appropriate temperature to permit air to pass out, or closes to stop the loss of air during cooler/colder wheather.


Our’s had a fluid that expanded as it heated pushing on a plunger/ram that pushed the vent open. They sometimes needed servicing for the seal around the plunger as it would perish. I think the fluid was an alcohol but it may have been something else, the local AC servicing guys did the work. In the NT these were already fitted to the house before we moved in. In the Isa we fitted them when we moved in.


It is also worth investigating how your roof space drafts or does not.

Installing any form of roof top vent system to let hot air out needs a corresponding way for cooler air to get in. Some heavily insulated roofs may have effectively closed off under eave ventilation and the gaps under the gutter ends of the roofing material.

If there is insufficient eve and gutter edge leakage, or freely flowing eve vents the air flow will stall at the fan or whirly bird, or natural convection vent. IE no benefits.

On whether there is any benefit in ventilating the roof space, the following handbook contains data tables with ventilated vs unventilated roof spaces and various insulation strategies. I linked this previously in another discussion re roof insulation.


The following table extract for a metal standard pitched roof demonstrates the differences between a sealed vs ventilated roof space. While it may seem counter intuitive the air in the roof space actually slows the transfer of heat from the roof metal to the ceiling. The outer metal (colour bond etc) at noon will be hotter than the air in the roof space if that helps understanding. Thermal gradient.

The table assigns R values to all the elements in the roofing and ceiling. This avoids complicated thermodynamics as it reduces to a simple additive solution.

Look at the line label Element 5, Attic Space.
For an insulated roof the dead air in a sealed (unventilated) roof is equivalent to R0.28 insulation in summer. IE not much. In comparison if the roof space is ventilated the summer benefit is slightly better equivalent to R0.46.

Look at the lines all labelled with 6.x (for ceilings with R3.5 or higher rated insulation).
It is very evident that once ceiling batts are installed whether there is or is not a ventilated roof space the difference in overall insulation benefit of ventilation is not significant, IE R0.2 in R3.9 total, or approx 5% improvement at best.

Higher rates of powered ventilation may improve on the small benefit. It’s worth considering that in more humid environments drawing warm moist air into a well insulated and cooled roof cavity (over night) early in the day will lead to condensation accumulation.

Ventilated roof spaces are definitely cooler in summer. Forced ventilation can improve this ultimately to achieve close to ambient in the roof with high air flows and under sheeting or tile insulation. The science suggests your mileage may vary.


Removing the roof access (“manhole”) cover should be similar to forcing the air with a fan, I do this here to remove hot air accumulation near the ceiling.


The eldest son of a lifetime mate of mine developed this roof ventilator many years ago and has obviously expanded from just doing houses.


No moving parts and apparently cyclone proof.


The venting of our roof helps our ducted AC work better. As the cavity no longer gets very hot (even considering the insulated ducting) the difference is quite noticeable. In Winter we block the whirlybird vents to retain cavity warmth. What we notice is less heat during hot periods than before the venting. We have R4.0 batting as well, prior to the vents/whirlybirds. Each degree less we have to contend with means less electricity usage and it pays to do so for us. Others may get less benefit than we do depending on their system or lack of cooling system.


What was unwritten is that benefits can be financial, or can be through interior comfort levels regardless of the heating or cooling systems installed.


Intuitively they seem like a good idea. I researched them a while back and simply couldn’t find any empirical evidence to prove that they’re worth bothering with at any cost (even George Gregan couldn’t convince me although as a promoter of roof ventilation he makes a very good rugby player).

This applies to a Whirlybird or something powered. Acknowledge @grahroll comments re venting making a difference to ducted air temp though.

IMHO the best option is to spend the money on more/better insulation and/or efficient heating/cooling.

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Another reason to ventilate the roof space could be to prevent cold water from heating up excessively. Coincidentally, I visited my old place of employment today and suggested to the practice manager that they consider Whirleybirds. On very hot days, the cold water becomes too hot to use. I had been told that the waterpipes were in the roof cavity. This roof space is fairly restricted in size, with a metal roof of low gradient in an 11 year old building. Would ventilating the roof space be likely to make a difference to the cold water temperature?

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Welcome to the community @tim3

If the cold water pipes run through a very hot ceiling cavity it would since the pipes get hot and thus become water heating elements.

If you run the cold water long enough to drain and then cool those pipes you should eventually get cold(er) water (as it comes from the ground).

The cheapest treatment would be ventilation from the soffits through a solar whirlybird or power fan. Wind-powered whirlybirds may not be effective because of the flat roof (heat rising to the peak of a roof cavity is one of the reasons they are placed as they are, and why they work as well as they do).


We have mechanical ventilation in our roof space. It works very well. We switch it on on a hot day and obviously don’t during winter. It’s inexpensive to run. The only down side to it is the noise. We have it vented into our garage so it doesn’t affect our neighbours. The noise can be heard from some rooms in our house but not all. The noise doesn’t bother my husband, but it bothers me.


Thanks @PhilT for that advice. Solar or power fan does make sense. Condensation in inland regional NSW shouldn’t be a problem for much of the year. It sounds as though being able to turn a roof space ventilating fan off from inside would be an advantage. I presume that this would be possible with powered fans, but is it possible with solar powered fans? Noise from a powered fan would be a disadvantage for this business. I would hope that a solar fan would be quieter.

I have also been getting quotes for our roof restoration in Lake Macquarie (including Whirlybirds). After some of the above advice, I may give Whirlybirds a miss and just insulate the garage ceiling (to cool the attached garage in order to improve the spare fridge efficiency). The rest of the house is insulated. The roofer said that their company are not allowed to work below the gutter line, and therefore are not allowed to install air inlet vents under the eaves. Someone else needs to do that work, increasing the chance that it will not be done.

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Some models have thermostatic controls or a similar option, so yes. Noise seems to vary from almost nil in a practcal sense, to roughly a typical fridge, to identifiable as a fan motor. Check the advertise/claimed db specs. <40 is very quiet. 60 is noticeable to most of us.

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