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Topic # 240748 24-Sep-2018 11:22
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Hi. 

 

So, we have 3 bathroom fans in the 3 bathrooms in our home. All 3 are cheaper noisy fans and at the home show we came across a model which is super quiet so we were keen to change them over. 

 

 

 

All 3 are "inline" fans into ducting which leads outside. The ducting is 150mm which is then changed to 100mm ducting via an adapter. 

 

I am wondering how big a deal it is if the outside grill/vent is 100mm, but the fan is a 200mm fan with a 200mm connection (incidentally, it's not so much inline as the fan is at the intake part, directly above our shower).

 

The fan says it will move around 440L per minute. Am I better to put up with our noisy current solution (which I am guessing moves around 200L/M of air) or should it be ok to change it over?

 

 


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  Reply # 2095564 24-Sep-2018 14:45
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A bigger fan on a lower speed will be quieter than a smaller fan at higher speed. Assuming the same air throughput and a bunch of other stuff. That being said, inline fans are generally quieter than inlet mounted ones as their noise is further from the opening you're hearing it come through. 

 

I reckon the choice is yours but don't blame me if it's no better...


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  Reply # 2095870 25-Sep-2018 03:23
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It depends a lot on the fan type. The cheap propeller style fans don't produce much pressure. So would be terrible on your style of ducting.

Centrifugal fans produce more pressure, so work far better on long / restrictive ducting.

Definitely upgrade the outlet size if you can. Going from 100mm to 150mm will approx double the airflow capacity, and 150mm to 200mm will approx double it again.





 
 
 
 


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  Reply # 2099676 1-Oct-2018 22:19
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networkn:

 

Hi. 

 

So, we have 3 bathroom fans in the 3 bathrooms in our home. All 3 are cheaper noisy fans and at the home show we came across a model which is super quiet so we were keen to change them over. 

 

 

 

All 3 are "inline" fans into ducting which leads outside. The ducting is 150mm which is then changed to 100mm ducting via an adapter. 

 

I am wondering how big a deal it is if the outside grill/vent is 100mm, but the fan is a 200mm fan with a 200mm connection (incidentally, it's not so much inline as the fan is at the intake part, directly above our shower).

 

The fan says it will move around 440L per minute. Am I better to put up with our noisy current solution (which I am guessing moves around 200L/M of air) or should it be ok to change it over?

 

 

 

 

 

 

Which product are you looking at out of curiosity? I was looking at Weiss products with EC motor and awaiting quote... seems expensive though.


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  Reply # 2099684 1-Oct-2018 23:48
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I put in a big manrose inline fan with a timer/delay about 6 months ago - directory above the shower. No steam at all on the ceiling anymore, and it's much quieter than those 150mm fans mounted on the ceiling units. Having said that, I think it could be quieter still if I suspended the fan from elastic cords. 

 

 

 

HRV install something they call 'Vortex' which is a 550m3 per hour unit - I found Simx has a very similar style model for a bit less if you have a particular moisture issue.


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  Reply # 2099691 2-Oct-2018 01:02
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We've had both 150mm (6") and 200mm (8") inline ducted fans installed in different bathrooms and the observable increase in airflow is about double. Between 150mm and 200mm the cross section increases 78% (1.78 = 225:400) while wall friction only increases 33% (1.33 = 300:400) because the circumference increases proportional to the diameter. Here's an example from https://russellking.me/2012/08/19/duct-size-vs-airflow-part-1/

 

Duct diameter: Air flow

 

100mm (4") 20
125mm (5") 50
150mm (6") 80
175mm (7") 120
200mm (8") 170
225mm (9") 230
250mm (10") 300

 

A couple of years ago we installed one of the cheapest ducted fans you can get at NZ hardware stores. It is noisier than any exhaust fan we've had and the noise has barely reduced with 1.5m of ducting and suspending it above the ceiling joists - the sound appears to mainly travel inside the duct rather than through the ceiling. So I'd say to avoid 150mm (6") ducted fan kits that retail under about $130 unless you can hear them running before you buy them.

 

We have also installed exhaust fans which are not the quietest but work very well because they have larger duct sizes, typically 200-250mm (8-10"). We currently have one of these where the lower fans speed and larger ducts combine to generate much less noise than the ducted fan I mentioned above.


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