What's the best way to install a through wall extraction fan

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Patient123

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Wannabe Geek

#258682 15-Oct-2019 20:34

My DIY project is replacing my 100mm extraction fan in my bathroom for a 150mm. It's a through wall extraction fan with weatherboard on the exterior. The size means I will need to somehow make a flat surface on the weatherboard to mount the exhaust side to. Has anyone got any tips?

I've already bought some 150mm Manrose standard fans

I've been told to use cardboard to get a profile of my weatherboard and then get a piece of wood cut to fit like a puzzle piece on top of the weatherboard.

I also watched a youtube video where they cut a square out of the weatherboard and didn't bother with the cut out.

timmmay

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#2337705 15-Oct-2019 20:49

You can just mount whatever on the outside and fill the gaps with sealant / silicone - not sure if it's a good idea but it works. I have that for my clothes drier exhaust, but the weatherboard is fairly low profile, 10mm.

Through wall fans are typically relatively low throughput, though by using a bigger fan it'll work better. Probably not practical, but for others considering this ceiling duct fan with a decent extractor, something like this or this has double or triple the throughput. You need an outlet in the eaves to push the wet air out.

mdf

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#2337718 15-Oct-2019 21:02

If you've got bevelback weatherboards, you're after a "scriber". Bunnings has these pre cut, but they may or may not fit your weatherboards. It's not _too_ hard to cut your own, particularly for a small bit around a fan. Scott Brown has a good how to:

You can use a jigsaw or handsaw instead of a table saw if you're only making little ones.

Fred99

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#2338135 16-Oct-2019 15:01

Another suggestion is that if the house has a typical pitch roof with eaves, then the level of the exterior soffits may be a couple of hundred mm lower than the top plate on the exterior wall. If that's the case then there's room to fit the interior vent at the top of the internal wall, run duct to and in line fan unit suspended from roof framing in the soffit area (less noise than having the motor built in to the vent), and vent it to the outside under the soffit. Downside to this is that you'll probably need to work through the 150mm or so hole you cut in the soffit for the exterior vent grill, to connect the ducts to the inline fan unit etc. Make sure the in line fan unit fits through the size hole you need for the vents.

If you ceiling mount it, then you may not have 150mm clearance above the top plate to get the ducting through to the roof space above the soffit.

mattwnz

20164 posts

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#2338162 16-Oct-2019 15:45

If dealing with soffits on an older house, these can be asbestos sheeting, so I would get it tested before mucking around with it.

Zeon

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#2338352 16-Oct-2019 18:10

mattwnz:

If dealing with soffits on an older house, these can be asbestos sheeting, so I would get it tested before mucking around with it.

Out of interest how would you know if this is the case? Electricians broke the Soffit at my place and not sure whether I can replace or the buidlers will replace if they are worried it is asbestos?

Speedtest 2019-10-14

mattwnz

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#2338382 16-Oct-2019 19:12

Zeon:

mattwnz:

If dealing with soffits on an older house, these can be asbestos sheeting, so I would get it tested before mucking around with it.

Out of interest how would you know if this is the case? Electricians broke the Soffit at my place and not sure whether I can replace or the buidlers will replace if they are worried it is asbestos?

Good question. It maybe able to be accessible from inside the roof space. But also the age of the house may indicate whether it is likely or not. Our old house was built in the 50s and had fibre cement soffits, so we guessed it would very likely be asbestos. There is likely to be an unpainted cut edge somewhere (eg underneath a soffit vent cover) where it can be tested from.