How effective is a whirly bird at cooling the roof?

I get enquiries very often about installing a ‘whirly bird’ (roof ventilator) to cool the house.

Whirly birds do not do any cooling. That is: they will not lower the temperature and more than the ambient.

Then just ventilate.

But ventilation is better than no ventilation and if installed correctly, they can provide airflow (sucking in cooler air and expelling warmer air).

whirly birds and roof attic ventilation diagram

The diagram shows how a whirly bird can ventilate the ceiling space. Whirly birds just by themselves are not very effective. They require vents (either in the eaves or in the ceiling of the house) to let cooler air in as the warm air is expelled through the turbine. So, if you are getting whirly birds installed, make sure that there are adequate ceiling vents to allow air replacement.

Also, whirlybirds are less effective if you have no sarking under the roof. A closed attic space is needed to force the whirly bird to draw air through the vents. Otherwise the whirly bird will just draw air through the gaps in the roof tiles locally and not produce much cross ventilation.

So, how effective a whirly bird will be for your roof depends on what sort of roof you have…

…if you don’t have sarking under the roof tiles or a decent roof overhang to install eaves vents – then you may be wasting your money on whirly birds.

The key is in installing a ventilation system containing whirlybirds rather than just installing whirlybirds by themselves… or perhaps a different roof system.
If you want to find out more, go to this website’s HOME to start your journey.


 Update:  16th October 2013

Last week, we put in some “new’ roof ventilators on a roof in Greenacre, Western Sydney.

They were not whirly birds. These were the first “Universal Tile Ventilators” we have installed. It was an easy installation and we are waiting for the client (who sourced the ventilators himself and asked us to put them in) to give us some feedback on it’s effectiveness in providing cross ventilation to his ceiling cavity.

Update 18th October 2013

We had a hot windy day on yesterday and my Greenacre client reckons that his house is cooler due to the Universal Tile ventilators….


50 responses to “FAQ – How effective is a whirly bird at cooling my roof?”

  1. roger says:

    would the bathroom ceiling ventilator would help even if switch off? or is it better to have a eaves vent? and how many vents? 2 on each side of the house? or that is too much?

  2. Jack Yuen says:

    Hi Roger,

    Like most things in life, there is no definitive answer to your questions.
    A bathroom ceiling ventilator – if it is ducted through the ceiling cavity and out the roof, will let hot air escape from the bathroom to the outside even if switched off.

    Eaves vents allow air to enter the ceiling cavity only. They have no effect on air circulation in any inside rooms/spaces. They work in conjunction with whirly birds (usually 2 vents per whirly bird) to circulate air through the ceiling cavity area.

    Hope this helps.


  3. Pat Robinson says:

    Whirlybird and twista seem to do the same job with only minor differences. Is one more effective and better made than the other ? When being installed will the tradesman also instal eave vents ?

  4. Jack Yuen says:

    Hi Pat,

    I have not done any testing between the brands. So, I don’t know which ones are more effective in drawing the hot air out.
    A tradesman who understands how whirly birds work (and reads the instructions from the manufacturer!) will allow for installation of eaves vents.

    There is a catch.

    There is no sure way of easily finding out if the eaves are fibre cement sheeting or asbestos. (Although the age of the house will give a clue). Tradesman should not be cutting holes in asbestos eaves.

    That is why the ‘universal tile ventilators’ (even though they are more expensive per pair) are perhaps the better solution if you have asbestos eaves.

    Hope this helps.


  5. Jon says:

    We have a house with raked (cathedral) ceilings. I am not sure of the setup of the roof (insulation etc.), but we have to rely a lot on using air-conditioners to keep the house cool. Would whirlybirds be useful in helping to expel that hot air that accumulates in our ceiling and make us a little less reliant on using airconditioners? It’s only a one-storey house as well.

  6. Jack Yuen says:

    Hi Jon,

    Whirlybirds are designed to vent the ceiling cavity – rather than the living space. Air conditioning is still the most effective cooling for living spaces.
    However, Edmonds make a cathedral ceiling venting system that can help vent living spaces. Details at:

    Edmonds also do ‘Odyssey’ – which is a more high tech ventilation system for living spaces – although this can almost be a expensive to install as an air conditioner.

    Hope this helps.


  7. Michael says:

    I have a double storey home with a large 3 storey open area with west facing full length windows. Area gets frightfully hot in summer even with window shades and double glazed coated glass. Problem is the hot air rises to the top and can’t be ventilated. We are debating between Odyssey to suck the air out or putting a fresh air filtered intake to the upstairs HVAC and run fan mode to draw in outside air (we have multiple ducted vents to the open area) interested to hear your thoughts on what’s more effective

  8. Jack Yuen says:

    Hi Michael,
    I may be good at fixing roof leaks.
    But I am hopeless trying to be an air conditioning engineer.
    I can only offer a few comments that may be helpful…

    … When I get into my ute on a hot day, I open the windows or doors to let the trapped hot air out.
    Then as I drive off, I put the A/C on and turn the vents to recirculating.
    The theory is that it is more efficient to cool recirculating air than it is to try to cool a stream of fresh air.

    … If the day is not too hot, I can just open both windows and this cools the cab down without A/C. This is what the Odyssey is supposed to do to the house (although the analogy will be with the ute windows both opened a fraction).

    If the day is stinking hot, then the only way to keep cool is air conditioning.
    If the ambient outside air is not too hot, then just leaving the windows open may create a draft and allow the hot air to escape…


  9. Glenys Howard says:

    We have a 30 year old cedar one storey home with cathedral ceilings in the lounge. We have whirly birds on the roof and the ceiling vents are in the lounge. It is very hard to heat the home.
    Can we cover the vents so that we stop heat loss in winter.

  10. Jack Yuen says:

    Hi Glenys,

    Most people have the opposite problem – too hot in the summer time.
    You can cover the vents to stop the warm air from escaping in the winter.

    Also, some cathedral ceilings do not allow for space to insulate the roof effectively (or maybe substandard insulation has been installed). This will make a huge difference.

    Hope this helps.


  11. cynthia says:

    Just found out that out bathroom exhaust fan are not connected to anything. All the steam from the bathroom released into the ceiling cavity. My question is I have someone suggested to install a whirlybird on the roof. Is this enough to remove the steam from the ceiling without connecting it to an aluminium flexible duct?

  12. Jack Yuen says:

    Hi Cynthia,
    A ‘closed’ system like using a flexible duct connection is the optimum solution.
    A whirly bird installed vertically above the bathroom exhaust is a good compromise – since warm air always want to travel upwards and a whirlybird is the least form of resistance for the escape of the moist air.


  13. Theron says:

    Hi We have a new (ish) home extension, I have noticed that the extension does not have eaves vents. The older part of the home does have eaves vents. Would installing a whirly bird in the roof of the extension still be effective ?
    Thanks in advance

  14. Jack Yuen says:

    Hi Theron,
    If the extension has a pitched roof, you can put in whirlybirds together with new eaves vents.
    That may work.


  15. Nick says:

    HI Jack, I am undertaking an attic conversion in a terrace house – going to install some under ceiling insulation ( 6mm kingspan) then seal up the ceiling space with walls and yellow tongue flooring – the only ventilation will be from the attic ladder – will a whirly bird work to remove the hot air build up when attic ladder trader is closed or only work when the attic ladder is pulled down leaving a “vent ” Any suggestions for his scenario ?? I have no eaves – thnx!

  16. Jack Yuen says:

    Hi Nick,

    In theory, you can install a whirly bird near the top ridge that can vent the attic space. But you do need an inflow of air into the attic to replace the hot air that rises to the top of the attic.
    So, when you pull the attic stairs down, this will allow this inflow of air.

    If you want airflow into the attic with the stair closed – you can cut a vent in your ceiling/and yellow tongue flooring.

    You can cover the ceiling vent in the winter time to stop the heated air from escaping from your cosy upstairs rooms…


  17. Stefen says:

    I have a beechwood home, it has concrete roof tiles and no sarkng.
    The roof space gets at least 20C hotter than the outside ambient temperature.
    i also have duced airso want to lower roof temperature and hopefully improve air con effiiency.
    The roof has no eaves vents .
    Ii am thinking of adding eaves vents and installing edmonds airomatic units.
    My roof area is 200 square metres.
    Is this a good idea or are there better ways to do it.

  18. Jack Yuen says:

    Hi Stefan,
    You will need a couple of eaves vents per airomatic unit (as per Edmonds brochure). It will probably help in lowering the attic temperature a bit.
    The other thing is to check the condition and rating of the ceiling batts on the ceiling. It may be worth adding another layer of batts (crossways) on top of the existing to increase the insulation at the timber joists (the timber gets hot too and makes the ceiling hot).
    Hope this helps.


  19. james says:

    I have a metal building that is used for a shop. The walls are insulated but roof is not and it is open from floor to ceiling. Would whirly birds help draw the heat from shop.

  20. Jack Yuen says:

    Hi James,
    I think whirly birds will help.
    As soon as you let cooler in from an opening like a door or window, it will displace the hot air at roof level which will escape through the whirlybird.


  21. Karen Lenehan says:

    Hi Jack,
    I have just got up on my tiled roof and jammed a tile in the whirly bird to stop in spinning with the belief that it will stop heat in the roof cavity escaping and therefore keep the house a bit warmer.
    Do you think there is any merit in this idea?

  22. Jack Yuen says:

    Hi Karen,

    Good try!
    Personally, I don’t think it will make much difference.
    The ceiling cavity gets warm during winter days – but cools quickly as it gets dark…. whether there is a whirly bird present or not.
    So, a whirly bird does nothing for keeping the ceiling cavity warm.
    You will be better off investing in better ceiling insulation.

    Hope this helps.


  23. Carolyn Richardson says:

    Hi Jack,
    We have condensation issues in our roof in the colder months. Will a whirl bird help this?

  24. Jack Yuen says:

    Hi Carolyn,
    I think a whirlybird can help with condensation – by letting the warmer moist air to escape. You will need eaves vents to aid in the air flow.


  25. Ryan says:

    Hi Jack,

    I live in a 2 storey home with no roof sparking, as I have colorbond. The roof gets extremely hot in the summer, and I have ducted aircon. What’s my best option? To instal a large whirlybird on the first floor only?

  26. Jack Yuen says:

    Hi Ryan,
    A colorbond roof should still have a building blanket under the roof sheets. If you don’t, then you can get substantial heat radiated into your attic space.
    A whirly bird (together with proper air inlet vents), will allow some of the hot air to escape.
    The most effective way to insulate a ceiling is high quality (R rating) ceiling batts…. not whirly birds.

    Hope this helps.


  27. Justin says:

    Hi Stefen…. did you get the eave vents installed and whirlybird/airomatic? Did you notice any difference? As I have a similar roof with concrete roof tiles with no sarking. Any feedback would be greatly appreciated.

  28. zongyi luan says:

    Hi, Jack:
    Very appreciate you say that “The most effective way to insulate a ceiling is high quality (R rating) ceiling batts…. not whirly birds.”
    Now I believe you are an honest expert.

    who speaks Mandarin

  29. Debbie Dunn says:

    Hi Jack,
    We have a Jennings home built 11 years ago, it has a colourbond roof, with the blanket and insulation in the ceiling and walls. We live 5 minutes from the ocean. Our problem is we keep getting white mould on furniture eg wood, leather, our clothing, shoes, handbags etc. I’m spending my days cleaning, flipping furniture to spray with vinegar. I have had a bout of pulursiy 2 months ago and I’m sure it’s from the mould, and keep getting a cough that won’t go away. We borrowed a friends dehumidifier last night and placed in our walk in wardrobe and the container had about 3 litres of water in it over 16 hours, to my amazement. The humidity level was 73% when we turned it on at 9pm last night. About 6 years ago, I rang someone to come in and look to see if they could tell us what our problem was, he charged $75 did no tests and we are still living with this problem. My question is would Whirlybirds help our situation ?

  30. Jack Yuen says:

    Hi Debbie,

    Whirly birds are designed to vent the attic space above the ceiling.
    They do nothing to the air movement in the living space. So, whirly birds will not help.
    Best to investigate ways to lower the humidity instead.
    Hope this helps.


  31. Dan says:


    In December of 2018 sprinkler system piping in the attic of my 4 story condominium building froze resulting in water damage to several units. Upon investigation by a sprinkler maintenance company
    consultants, the condo management company was advised to insulate exposed pipes in the attic and/or install a means of heating the attic space. Nothing was ever done.

    In February of 2019 the same condo management company chose to do roof repair work in the same building in February even though they were fully aware of what happened the previous winter. The contract was awarded by the management company to a single contractor without requesting bids from other competing contractors stating that to entertain other bids would require an expense by the condominium complex of thousands of dollars. This seemed incorrect as usually any cost incurred by bidding contractors is an expense they endure as a means of winning the contract.

    Furthermore IF we paid the contractor for discovery work in reviewing the disposition of the roof
    the resulting findings (report) should have been the property of the condominium complex which we
    could have made available to any competing bidder.

    So with the contract awarded to the one and only bidder they chose to open the roof in the middle of February without doing anything to protect the attic sprinkler piping and while outside temperatures were in the single digits! Furthermore during this time they also installed on the roof
    six, four feet tall non-powered whirlybird ventilation units.

    Well the pipes froze and 30 units got flooded. I am not living in my condo at the moment having been forced to leave while repairs are made. I believe that the management company is in cahoots with the contractor and the whirlybirds (which mysteriously have since disappeared from the roof having been replaced by fewer smaller units) were deliberately put in place to cause the failure.
    And not only did this happen in one building but it actually happened in two buildings within an hour or so of each other.

    I would appreciate your opinion on the possibility that this was deliberate.

    And as you probably could have guessed the management company has chosen the same contractor potentially negligent in the roof work to be the contractor to do all the reconstruction work internally!

    Again, I would appreciate your opinion on the possibility that this was deliberate.
    I and several other owners are considering legal action as the management company has provided little in the form of restitution of any kind throughout this entire ordeal.

    Thank you,


  32. Jack Yuen says:

    Hi Dan,

    I cannot comment about the relationship between the management company and the contractor – because I do not know all the facts.
    Also, it is unlikely that they would deliberately sabotage the sprinkler system – rather they may have made a series of mistakes in doing the work in the middle of winter and in installing the whirlybirds.
    The large whirlybirds would release any warmth in the attic space during winter and bring on colder temperatures.
    In hindsight, priority in insulating the sprinkler pipes should have been made.
    Hope this helps.


  33. julie says:

    Hi Jack,
    I have a two story cathedral ceiling house, exposed beams, no insulation and the entire west facing wall is glass – it is unbearably hot in summer!
    We are considering enclosing the beams and installing insulation but this will be expensive and lose the character of the house. Alternatively would whirly-birds remove the heat and are the ok to use in cathedral exposed beam ceilings?
    Any advice would be appreciated

  34. Jack Yuen says:

    Hi Julie,

    Whirly birds can be installed ( which connect to ceiling grilles in your cathedral ceiling), and they will let hot air escape from your upstairs living space.
    However, in the winter time, the warm air in this living space will escape through the whirly birds and give you a cold house….

    Maybe a solution is to put in an opening skylight that can let the hot air escape in summer and keep it closed in winter?


  35. Batwam says:

    I agree with the skylight/velux solution and recommend a system with automated closing (rather than manual) which can be left open during the day to ventilate without having to worry about it staying open if it starts raining…

    This said, based in my experience, this won’t be sufficient as it doesn’t block radiated heat. Put as much insulation as you can between the beams and enclose the gap if you actually want to fix the issue.

  36. Matt Jones says:


    We have a flat metal colorbond roof that has metallic insulation on the underside of the roof. There is little or no insulation on the ceiling side. It has a large roof space and we have 3 whirlybirds installed. Are we losing a lot of heat in winter time?


  37. Jack Yuen says:

    Hi Matt,

    During the winter time, cold air gets in between the underside of the ‘metallic’ insulation and your plasterboard ceiling (courtesy of your whirlybirds and other air passages).
    At the same time, you are trying to heat your living spaces and the plasterboard ceilings will get all the warm air. You get a nasty heat transfer action where you are heating one side of the ceiling and the heat is sucked out by the cold air on the other side.
    That is the reason for ceiling batts. They keep the cold air away from the top side of the warm plasterboard ceiling.

    So, the answer is YES.
    You are losing heat.

    Hope this makes sense.


  38. Dave Jordan says:

    Hi Jack. Do you have an opinion on the difference between powered roof ventilators or just whirly birds

  39. Jack Yuen says:

    Hi Dave,
    I would suggest a solar powered ventilator.
    Logic being that you want extraction when the sun is out and it is getting hot. The wind may not be going that strong on long sunny days…


  40. Paul Joswig says:

    Hi Jack, thanks for all your assistance to people here, and I hope you can assist me as well. 🙂

    I have thought up a plan for my roof cavity ventilation, and I am wondering about your thoughts.

    I am thinking of using ducting and inline fans, rather than whirly birds. I would create eave vents to allow air in, and the ducting would start high in the roof cavity and end at other eave vents.

    The idea being to use fans to suck the hot air from high and expel out the eaves.

    Reasons: we have solar, and so it avoids potential shadowing from whirlies, as well as erratic performance, and sucking air out when we don’t want it to (I.e. cold days). The fans will easily be powered by the solar when it’s hotter months, so no running costs.

    What do you think?

    Also, what are your thoughts on capacity… E.g. how many times per hour should we be looking at exchanging the roof cavity air?

    Atm I am thinking of two fans at separate ends of the house, but it’s Just a guess that’s it’s enough or necessary.

    By the way, a separate project is to duct the two bathroom fans and the stove exhaust fan to the eaves as well. At present they exhaust to the roof cavity.

    Thanks and regards
    Adelaide SA

  41. Jack Yuen says:

    Hi Paul,
    I think we need to back to basics – before we get carried away with large effort/small gain projects.
    I like to picture ceiling cavity insulation as a refrigerator.
    The walls of the fridge are so well insulated that it does not matter what the outside temperature is… the inside still stays cold.
    Therefore if you are able to insulate your ceiling like the walls of a fridge, then the attic temperature has no effect on the living space temperature.
    Which means you get more ‘bang for bucks’ by concentrating on ceiling insulation instead of controlling the attic space temperature.

    The bathroom and kitchen exhausts should be duct-vented to outside the roof cavity.
    Hope this helps.


  42. Bob m says:

    My son accidentally did that (vented into the attic) and I ended up having to replace the roof and a number of plywood panels above the fan exhaust rotted from excessive moisture. The roofing guy vented the exhaust fan outside the attic with a roof vent.

  43. Keith Edward Tupper says:

    We have had our Breezair unit serviced, partly because we thought it may be responsible for the continuous knocking sound coming from the roof on a windy day. The service man told us the unit was sound, and would not be responsible for the knocking sound. But he told us we have a whirly bird (having moved here five years ago we were unaware of this, as it is completely out of sight from ground level), and that may be responsible, although as far as he could see it was all right.
    Can you throw any light on this?

  44. Jack Yuen says:

    Hi Keith,

    It could be the whirly bird.
    I suggest just replacing the whirly bird and see if the noise goes away.
    This is an easy elimination strategy.


  45. David higgins says:

    accidently? He put a fan, from the bathroom, into the roof cavity. sorry, but that’s not an accident. You wouldn’t take the garden hose, put it through an open window and then say “whoops, my bad…”

  46. dick hamilton says:

    um, putting the heater on would do something for keeping the ceiling cavity warm, that would be if the warm air was not being sucked out by the whirly bird. For some reason all you experts, literally all of you keep telling people whirly birds wont suck the warm air out of the roof in winter… What is there function Jack??? That is there function!!!!!!!!!!! SO yes, they will suck the warm air out of the roof Karen. You will need to design and install a way of block it from underneath. An aspect that every manufacturer and installer of these products have failed to consider or mention…. !!!!

  47. Anthony Kayondo says:


    What is the best way for cooling a concealed roof on a bungalow house with a single pitch. The single pitch angle is quite small and there is a gypsum ceiling(We don’t have winter where I am). The heat is excessive in the ceiling area. We put louver ventilators but their design bars proper air flow to cool the ceiling area. Will the whirly birds be of any help?

  48. Jack Yuen says:

    Hi Anthony,
    Every situation is different.
    Generally, a whirly bird helps hot air to escape. It should be located as high up the slope of a roof as possible – because hot air rises.
    But there must be a air inlet lower down the roof to allow cooler air to replace the hot air that the whirly bird is trying to expel.
    The most effective temperature control method is always to insulate the ceiling – rather that cool the attic space.

    Hope this helps.


  49. Colin says:

    Hi Jack

    I have an old house which recently had roof leakage and mold have developed inside the house, would a whirly bird be helpful in keeping the ceiling cavity dry and hopefully prevent mold buildup?

  50. Jack Yuen says:

    Hi Colin,
    Mould loves dampness. So, if your ceiling is damp (from the leak), then drying the ceiling is the first step. This usually mean removing any soggy ceiling batts.
    Since the roof cavity will get pretty hot on a sunny day, the ceiling will warm up and dry itself off fairly quickly.
    Then, replace the ceiling batts in the roof leak area.
    Clean the mould (mold) off the ceiling with mould remover.
    If you did not have mould before the roof leak, then you should not have mould after this procedure.
    A whirly bird can ventilate the attic space if installed correctly. but it does not control the mould on your ceiling.


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