Solar Roof Vents - How Much Airflow (I.e. CFM) Is Needed to Make a Difference?

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  woody007 on 12/12/2018 - 21:38

  SolarWhiz solar fan ventillator i paid approx $650 ea installed.

  My home is close to 400sqm under roof and i have 2 of them, it seems to work well. You might need to put in snap in vents on the eaves to help assist with flow when its hot. I also have 2.7m roof inside and then it vaults up into my kitchen/living area to 4m approx. They seem like a good kit and its been 1 year since ive had it in. Id consider getting a thermostat trigger so the fan does not run all the time maybe to ensure the life of the fan.

  Cheers.

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  kickling on 13/12/2018 - 01:08

  I installed 2x whirlybirds (Edmonds Supavent) last summer. They have made a small difference. 1x onto colorbond roof and 1x over tiles.

  A lot of people say it's useless / unrequired on a tiled roof and that would be generally correct. But, I have been in the roof space before and after the whirlybird was installed (tiles) and you can feel a draft forming.

  But to take full advantage of any roof ventilator you need intake vents under your eaves.

  I looked into Solar ventilators too. The price was too much for very little improvement over manual whirlybirds, especially with a tiled roof. The general consensus from various forums was to look at other measures first, such as extra insulation or sarking.

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  [Deactivated] on 13/12/2018 - 07:36

  whirlybirds are a better option, as they are cheaper and will last much longer, I looked into solar vents and I doubt the electrics in them would last more than 10 years.

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  Ocker on 13/12/2018 - 11:22

  Airflow is measured in cubic metre per hour M3/ph. They say you should allow for a complete change of air in the roof cavity 6-8 times per hour. Multiply the surface area of your ceiling and multiply it by the approx average height of the roof cavity. So, if you have a 200sqmt house and the average roof height (ceiling to top of roof) is 1.6mt then the cubic volume is 200 x 1.6 = 320m3

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  jasonlv87 on 13/12/2018 - 11:58

  I bought this solar vent 9 months ago to replace a leaking whirlybird and so far I've been impressed. The whirlybird did a decent job at keeping the ceiling space cool but the solar vent has considerably higher airflow.
  The only con is it is definitely noisier than the whirlybird, and the noise changes constantly due to passing clouds. On a clear day with no clouds I don't really notice the noise.
  https://mjproducts.com.au/home-2/solar-roof-vent-17-watt-sol…

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  [Deactivated] on 13/12/2018 - 16:06

  Am I the only one wondering how CFM was converted to SqM?

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  BertieBrown on 13/12/2018 - 20:24

  +1

  If it were me, I would try a whirlybird first, and see how you go. If you can, try and measure the ambient temperature of a day outside the roof, measure the temperature within the roof and then when you've installed the whirlybird measure again, obviously there are a lot of variances that you can't really account for, such as wind speed, direction, and maybe humidity which might have an effect, but this might give you a bit of an indication of whether or not it would be worth getting the more expensive solar ones installed.

  Really, it's a matter of trying to move the energy within the roof cavity outside, so you'd imagine that you would need quite a few whirlybirds and intake points to move such a large amount of energy, but I suppose it also depends on how much of a difference only a few degrees might make.

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  iwearpants on 25/02/2019 - 17:04

  Bought the following solar vent from Bunnings:

  Acol 200mm Black Ezylite Solar Roof Vent

  https://www.bunnings.com.au/acol-200mm-black-ezylite-solar-r…

  Inspecting the item and holding it, I felt like it should be worth about $50 rather than the $170 paid for it.

  I think I will return it and get something more substantial. The JM brushless motor one looks interesting.

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  campanaris on 21/01/2020 - 16:41

  I am monitoring the improvements since fitting the 2 Solarking roof fans to my home to give others an idea of the change the solar exhaust fans have made.
  The house is 180Sqm single storey with a tile roof and 2 fans, temperature sensor is in the roof minimum 10M from each fan (sensor is in the middle of the roof place on the insulation). The roof has no foil under the tiles or in the walls and there are no under eave vents fitted but the roof is well insulated. The roof gets limited shade in the morning and none past 11am in summer time. The house has one fan on the north side of the roof pointed slight North West. The second fan is on the western side of the roof point North West.
  The house in summers prior to the fans being fitted reached over 70°. Here I have recorded some temperatures on extreme heat days below to give an idea of how much cooler the roof is now. The house has two aircon’s one small 3.2KW in a bedroom and one 6.5KW in the lounge room. Since installing the fans we can now just run the 3.2KW inverter aircon on full power to cool the whole house even on the 40+ degree days. Many days when the ambient temp is in the high 20’s low 30’s we no longer run any air conditioning let alone the big 6.5KW unit like before.
  Very Sunny day no cloud 43° max ambient temp, max temp in the roof 52.8°
  Sunny with some high cloud 40° max ambient temp, max temp in the roof 49.0°
  Sunny Day no cloud 32° max ambient temp, max temp in the roof 40.3°
  Cloudy day no sun 28° max ambient temp, max temp in the roof 30.2°

  Also I have noticed with monitoring the roof temperature very closely is how fast the roof cools at night once the sun goes down. Within about 3 hours the roof temp is the same as the outside ambient temp. I guess this is due to the roof temperature not getting as hot as before so it can get back to the outside temperature quicker.
  https://www.solarking.net.au/product/solar-roof-vent