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What exhaust fan for 290mm square cut out?

I have 290 mm square cut out in bathroom ceiling with a very old fan I would like to replace. It seems there is no exhaust fan available anywhere that can use 290mm square cutout. Most of bathroom exhaust fan requires circular hole of smaller diameter.

I have tried Mercator that needs 290mm diameter but that's too small to fit into 290mm square cut.

Also, 290 * squareroot(2) = 410mm. This is the diagonal length in 290mm square. So minimum hole I can make would be of 410mm diameter that is too big for any fan available.

Can you please suggest any bathroom fan that can fit right away or with some adjustments. Thanks.

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JacobZ

Hi @lk12,

Thank you for your question and welcome to the Bunnings Workshop community, it is fantastic to have you with us.

There is this Mercator 290mm White Plug-In Square Exhaust Fan with Tri-Colour LED Light which should in theory fit straight into the hole that you've mentioned.

You could also possibly use this Brilliant 325mm Astro DIY Plug-In Square Exhaust Fan With LED Light with some minor adjustments to the plasterboard.

Alternatively, you could patch the existing hole using a Gyprock Plaster Repair Panel and then create a new cutout. This would be fairly easy to do, and I'd be happy to offer you some guidance if you'd like to go down this route.

Let me know what you think and if you have any further questions, please don't hesitate to ask.

Jacob

lk12

Thanks Jacob for the information. Unfortunately, both fans have only square grill but hidden behind is round assembly that needs round cut out. I actually bought exact same Mercator Square only to realise underneath it requires round cutout and had to return. 290mm diameter assembly does not fit in 290mm square, the space left in corners would also nterfere with suction.

Gyprock repair seems only option. Can you provide more guidance on that. Thank you!

JacobZ

Hi @lk12,

First, start by confirming the thickness of the plasterboard. It is likely that it will be 10mm, but it's worth checking as there are other common thicknesses for plasterboard.

Once you have confirmed the thickness of the plasterboard, assuming it is 10mm thick, you'll need a pencil, a drill, 30mm plasterboard screws, a plaster repair panel, a plaster repair kit, 64 x 19mm DAR Pine and a jab saw.

Place the repair panel on the ceiling covering the hole and trace around the outside of it with your pencil, then use the jab saw to cut out the plasterboard. Once the plasterboard has been removed, use the 64x19mm timber to "back block" the hole. This is done by placing the timber half over the existing plasterboard and half over the hole and using your plasterboard screws, screw up through the existing plaster into the timber ensuring that the screws are at least 20mm away from the edge to prevent the plasterboard from fracturing. Once the timber has been screwed to the existing plasterboard, place the repair panel into the hole and screw through it into the timber.

See the below images as an example.

Once the repair panel has been fixed in place, ensure the screws are driven in far enough so that they slightly purse the paper without tearing. Then apply the mesh tape across the joins, ensuring it covers the screws. Once the tape is in place, mix up some plaster and apply it over the tape, feathering it out so that it the plaster tapers away from the join. If your first coat does not fully cover the tape, apply a second coat that is wider than the first.

After allowing the plaster to dry, you can sand it smooth with your sanding block, doing your best to make the transition from plaster to plasterboard as seamless as possible.

Now it has been sanded, paint the plaster to match the rest of the ceiling.

You can then cut out the new hole for your exhaust fan to be installed using your jab saw.

Let me know if this requires any clarification, I am more than happy to help further if required.

Jacob

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