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Hi, I have recently fitted a "whirlybird" to my roof, however as my eaves are asbestos, I'm wondering about alternative methods of providing "flow-through" to the ceiling cavity. Fitting internal vents to the ceiling has been mentioned, but I've read this may actually cause problems with hot air pushing down through the vent(s) into the house. Any ideas would be appreciated!
Western rotary vents actually suck air out of your roof space, not pull it in, so you're not going to have hot air "pushing down". However the reverse will happen and if you have open vents in your ceiling, the vent will suck the hot air out of your room in winter, which you obviously don't want.
I think that you really don't want the vent sucking air out of your room because it will just be replaced with warm air from outside - these things are designed to work by expelling the hot air from your roof space, so you really want vents to the outside, either through the eaves or through the roof. Or if you have gables you can install a gable vent.
You might find that it works well enough without vents because a roof space is rarely air tight anyway.
I have 2 fitted without any additional vents, and they spin day and night. There is more than enough air flow with a natural roof.
If you've got a tile roof, you can probably get away without puting in the vents. They would make the ventilation more efficent but hey will still work anyway... Stick you head up in the roof space, if you can see lots of light getting in, its probably a good bet there is also room for plenty of air to get in also..
If you've got a tin roof - that changes things.
I've 2 whirlybirds on the roof of my folks place and it made a noticable difference, I then put the eave vents in, they made a diffence but not a significant as the difference when i put the first whirly in.
I've even got one of the clear plactic ones and put it in the roof of my shed as a vent/skylight... Definately worth doing
They spin when the wind is blowing. Any wind if the bearings are good.
Hot air does not sink. Heat can radiate through still air. You would need a lot of heat and very little flow to get roof heat down into the living space. It would be radiating through the ceiling more than the vents.
If the air in your house is cooler than the air outside and you vent in the ceiling there is a danger hotter air will be drawn in and dump energy or mix with the cooler air within before venting up through the roof. Usually however this isn't the case (unless you've got an air conditioner going) and the net effect will be cooler and fesher air within the house.
Remember flow is driven by pressure and density. The variations are small so the "push" driving the air out is small, so you need to have as little restriction to flow as possible.
Wetting asbestos reduces dust to a minimum. Add a good mask and a wet and dry vacuum and you should be able to manage it. No doubt the safety police will lynch me for that, but remember my generation practically bathed in asbestos dust for half our lives.
2c.
We installed ceiling vents that can be closed. Its a 1 minute job every December and April to open / close them. Just make sure they are not so close to the eaves that the radiant heat send warm air down the vents.
Yeah, what the roof is made of is key.
Tiles will leak air and you don't need vents. This is my setup and I have 3 rotary ventilators.
If you have iron, eaves vents are a good idea but get them installed by professionals if the soffits are AC sheet. There is no safe level of exposure to asbestos fibres.