I have an existing issue with my bathroom ceiling fan, as detailed in this post: How to fix an ineffective Extraction Fan setup in bathroom

I now wish to change it to a Fan that:

a) Has a new motor, so it works b) Has an outlet vent that points upwards not sideways so the air can easily go to the roof vent

The IXL original (https://www.bunnings.com.au/ixl-tastic-original-3-in-1-bathroom-heat-fan-light_p4442438) seems to fit this requirement. However the cutout required is 262mm by 262mm as detailed on the third page here (https://2ecffd01e1ab3e9383f0-07db7b9624bbdf022e3b5395236d5cf8.ssl.cf4.rackcdn.com/Product/009c39d0-4f3b-4fd5-aacf-f58341f2d9d1.pdf)

My current ceiling aperture is 300mm by 300mm, which fits the Heller Silver Mason model (https://www.bunnings.com.au/heller-4-x-275w-led-silver-mason-3in1-bathroom-heater_p4441815)

I can either replace with exactly the same model, but I thought since I'm changing it over I may as well get one that has an outlet vent pointing upwards rather than sideways to suit the roof vent existing. Unless there is another reason they did not use one of these initially that I am missing (maybe debris that fall through the roof vent would get into the Fan?)

Any advice on how to fill the gaps that would be caused by using a smaller unit is appreciated.


  • You might want to check your local codes; in most cases ducting the fan outside is required, if not highly recommenced to prevent attic mold.
    – tahwos
    Jul 11, 2019 at 22:27
  • Yes good point. The current situation doesn't seem to be causing any mold to the naked eye, though that could change if I put an efficient motor up there. Did I mention there is a roof vent directly above where the unit fits into the ceiling. Problem is the Unit fitted has a side ventilation system, and there is no room to fit ducting to the roof vent (as there is only a 2 cm gap between the top of the Exhaust fan unit and the roof) I wish they had installed a unit that has outlet vent that points up in the first place, so I could just replace and no ducting required as it's a Flat roof
    – Chris T
    Jul 15, 2019 at 3:24
  • Yes, you mentioned that, but these are two totally independent systems, with totally different rules governing their application. Bathroom exhaust fans in my locality for example, must be routed to the exterior and they may not vent to an enclosed space, such as a crawlspace or an attic. A picture would help...
    – tahwos
    Jul 17, 2019 at 1:09

2 Answers 2


If you can't or won't patch, how about a picture frame?

enter image description here


I would make a wood backing plate to sit behind the hole, with another plate that fits into the existing 300mm aperture which has a 262mm aperture in it. The support comes from the backing plate.

Then final filling, smoothing and finishing as required.

  • The difficulty with this is that it is a flat roof (probably I should mention this in the Post) so fitting a piece of backing that is larger than the hole seems impossible
    – Chris T
    Jul 15, 2019 at 3:26
  • Omitting detail does not help us help you...
    – Solar Mike
    Jul 15, 2019 at 3:32

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