In-line extractor draw noise

31 Aug 2021
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United Kingdom
We are in the process of updating a 1980s house and have just had an inline extractor fan installed (Manrose MF100T). I chose this model due to the advertised low decibels

I’m concerned that that the air draw noise this is creating in the bathroom is so much louder than I was expecting. If I shut off the vent, you can barely hear the fan noise from the attic above

The electrician used the existing ducting that was there from the original ceiling mounted extractor fan

Is this old ducting potentially creating the air sucking noise when the fan is turned on?? Is there anything I can do to reduce the noise?

It’s so much louder than the fans we have had in previous properties!
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Concertina ducting or is it smooth solid plastic ducting?
Concertina ducting or is it smooth solid plastic ducting?

When I was up in the attic checking it it was the actual fan making the noise, I noticed some tears in it (only looked at the section that goes from the fan to the vent)

Not sure if this is potentially causing excess noise by sucking in external air etc???
Regardless of the noise, patch them up ASAP, as you don't want to be putting moist air into your roof space.
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Sounds like a poor effort and needs sorting.
When 5 inch kitchen hoods first came out electrician's carried on using a 4 inch core cutter and fitted a 5 to 4 inch adapter. This caused a back pressure of air and made the fan make a noise.
I think the same applies to bathroom fans although many are still 100mm.
Maybe the pipe you have is restricting air flow making fan noise.

Swap for smooth solid pipe.
I've used soil pipe and pan connectors to couple to fan as they fit a treat, but you can buy the proper pipe for extractors.

Maybe that concertina pipe is creating too much air pressure. Way to test if run fan without pipe attached. If fan is quiet you know its the first pipe
Smooth ducting (IE solid pipe) will give quieter air flow than the concertina stuff. A larger inlet and duct (don't go mad) will be quieter due to lower airspeed required to move the same volume.
Problem with rigid duct is you can then get mechanical noise coming back from the fan.
Pipe should have no bends or be squashed.
Just remove pipe and run fan. Make sure it's working OK
Thanks all. Will remove the old concertina ducting, check fan and replace with solid duct! Will report back if it does or doesn’t fix the issue!
Hi all. Before I start replacing the old ducting next week, I have 1 final question on the positioning of the fan. It’s currently immediately next to the bathroom vent, which is no doubt contributing to the noise issue. Is there an optimum location to place it? Half way along the run or as close to the external vent as possible etc?
If it is on the ceiling, or mounted on the ceiling joists, then the ceiling plasterboard will act like drum skin and amplify the fan noise.
There’s probable a better place to put it

Site it on top of a dividing wall, there will then be a solid base for the whirly thing.
In your first post you said the mechanical noise was tiny compared to the sound of moving air. If that's true and it's fixed to something solid then leave it there. You will reduce the airflow if you move the fan away from the input vent- which might be what you want?
@Philip Durrant sorry to revive an old topic. I am in the same situation as you. Did you manage to rework the ducting with solid one and did it make any difference at the end? Thanks.

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