How to replace old exhaust fans in bathroom and kitchen?

[joejoeinc]

I have 2x old Mistral wall exhaust fans that have a 300 mm x 300 mm shroud going through a 220 x 230mm hole to the outside of my home. I can only find 150mm exhaust fans at bunnings. Both these fans died a long time ago (they just rattle whenever you turn them on) They really need to be replaced.

I'm looking for advice as to what my options are? should I attempt to fill in the internal wall holes to make it a 150mm hole or should I try to source a like-for-like replacement? 

It looks like this product wouldn't even cover the massive hole that was made in the wall to accommodate these older fans. 
https://www.bunnings.com.au/blauberg-150mm-white-aero-wall-ceiling-exhaust-fan_p4420505

Here are some photos that show the issue I am dealing with.   

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[Jason]

Welcome to the Bunnings Workshop community @joejoeinc. It's great to have you join us. 

I'm sure this is a common challenge. Let me tag a few community experts in @EricL, @tom_builds and @CSParnell to kick off the discussion.

Looking forward to seeing how you can improve the effectiveness and appearance of your bathroom and kitchen fans. 

Jason 

[joejoeinc]

Thanks, Jason  I look forward to figuring this challenge out.

[CSParnell]

Hi @joejoeinc welcome to the community. You certainly have yourself some old school wall fans there and someone had fun installing them.

You have 2 options.

1. As you say purchase the same size wall fans and there are some much nicer and stylish looking ones out there of that size just do a google search.

2. You install some new plates and cut new holes to suit a smaller wall fan and mesh covered flap vent on the outside. I would probably fill in the outer of the pipe between the brick and the pipe with some expanda foam just to make sure the draft only went through the pipe and not the brick cavity.

@EricL any other ideas?

[EricL]

Hello @joejoeinc

Thank you for sharing your question about your exhaust fans. The old Mistral fans use to run at lower speeds and didn't draw out a lot of air in the process. The Blauberg 150mm White AERO Wall / Ceiling Exhaust Fan you've indicated has a capacity to move 300 cubic meters of air per hour. This is a high-velocity fan that can change the air in the room in a matter of minutes. 

To give you a perspective, a typical room that is 3 x 3 meters with a ceiling height of 2.4 meters has a cubic space of 21.6 m3. That roughly equates to the air in the room being emptied out every 13.5 minutes. There are of course mitigating factors that slow the air exchange in the room. The room could be very well sealed, this prevents outside air from entering the room except through gaps in the door and window. The room is too large which means that you'll need to use a different exhaust fan to ventilate the room.

Is there a possibility of transferring your kitchen exhaust fan to the ceiling? If it can be moved, it will allow you to use a large majority of the ceiling fans that the store offers. These ceiling units have a minimum capacity of 500 cubic meters and are ideal for use in large open areas. Due to the current sizes of wall exhaust fans, I'm afraid modifying the existing fittings in your kitchen and laundry room is unavoidable.

Please keep us updated with your progress, we look forward to seeing your new exhaust fans installed.

If you need further assistance, please let us know.

Eric

[joejoeinc]

OK so I've thought about this for a while and I think the plan for now is:

- Cut a length of 150mm PVC pipe to act as the new vent hole  (noting that the exhaust fan is also 150mm for the vent part)
- Grab a 150mm connector to make the end slightly wide enough for the exhaust fan. Add the connector to cut to length PVC.
- Grab this exhaust fan https://www.bunnings.com.au/blauberg-150mm-white-auto-wall-ceiling-exhaust-fan-with-automatic-shutte...
- Grab some expanding foam and some wood shims to prop up the PVC pipe in place 
- Grab some rapid-set concrete  (and gloves)

Method: 
- Remove the old exhaust fan. Kick it into the bin.  
- Insert PVC pipe into the existing wall cavity, making sure end of PVC pipe is flush with the internal wall. set  PVC pipe in place using wood shims and expanding foam. 
- Add some extra expanding foam around the place to prevent exhaust from venting into the wall cavity (as it had been for decades already) and also use the foam to create a temp wall to build concrete up against. 
- Use the rapid set concrete to build up around the internal wall and new exhaust vent hole.  (Fig 01)
- Install new exhaust fans paint and finish (a few coats of paint may be needed to smooth out the concrete finish to match the existing wall) 

Note:  The wiring block/terminal may also need to be moved after removing the old fan. I have a sparky on hand to assist with that. 

Fig 01: building up the hole with concrete

[EricL]

Hi @joejoeinc

That sounds like an excellent plan, I would only suggest adding a small trowel to your tool list so that you can do a nice finish on the concrete.

Please keep us updated with your progress, we look forward to seeing your exhaust fans installed.

Eric

[Alison2]

Hi @joejoeinc 

Do you still have the mistral fan by any chance? I have one and the plastic cover is broken in several places. I’d love to buy your old one off you if you still have it? 🤞

kind regards,

Alison 

 

[MitchellMc]

Welcome to the Bunnings Workshop community @Alison2. It's wonderful to have you join us, and many thanks for jumping into the discussion.

If you cannot find a replacement cover, you might be able to fashion a suitable repair by applying white self-adhesive film over the front face. You could then spraypaint the rest of the unit white to suit. 

Is it only the front cover plate that is cracked, or is the whole front assembly not fixed correctly onto the mount? If there is more extensive damage than the front cover, you might like to look at our range of wall exhaust fans to find a suitable replacement.

Please let me know if you have any questions.

Mitchell

[MikeTNZ]

Hi @joejoeinc,

Just bear in mind that because this is a bathroom, any fan you install, will either need supply from an RCD circuit or be supplied via an SELV (Safety Extra Low Voltage), meaning 12 Volts.

Gone are the days when you could just throw a fan in a wall in a bathroom, unfortunately.