125mm inline fan with 100mm ducting

[Cocat2517]

Hi
Will a 125mm inline fan suffer much of a reduction in performance if connected to 100mm ducting?

Thanks

 

[foxhole]

Mines been in a couple of years and still performs fine . There will be some loss of performance , is it kitchen .

 

[Cocat2517]

No, in a bathroom.

Also, can the ceiling vent for it go above the bath?

 

[Taylortwocities]

You’ll reduce the possible air through the duct by about 40%. Will that be sufficient air throughput to adequately clear the room? There are lots of room/fan calculators on the Internet so you can check.
Why not do it properly and use 125mm duct, etc.

The air inlet for an in-line fan can go anywhere you like. I assume it doesn’t have any electrical component (like a light) in it?

PS pedantic point: a vent is where the air extracts from, not where it comes in!

 

[Cocat2517]

Bit of a ball ache replacing all the ducting and the 100mm outlet vent in wall. If we're looking at up to 40% reduction in performance then I'll have no choice. The fan is rated at around 350m³/hour airflow and theyre going in a bathroom and shower room, both approx 3m X 2m.

 

[jj4091]

You’ll reduce the possible air through the duct by about 40%. Will that be sufficient air throughput to adequately clear the room? There are lots of room/fan calculators on the Internet so you can check.
Why not do it properly and use 125mm duct, etc.

The air inlet for an in-line fan can go anywhere you like. I assume it doesn’t have any electrical component (like a light) in it?

PS pedantic point: a vent is where the air extracts from, not where it comes in!

This article seems to disagree with you https://www.energyvanguard.com/blog/what-happens-air-flow-ducts-when-size-changes It seems that the flow is not reduced but the air pressure exiting the duct increases.

 

[rsgaz]

Aside from the performance issues, it will make more noise, I guarantee you. That would be enough for me to not do it.

 

[foxhole]

I used a 100mm Y joint allowing 2 vent points in the ceiling .

 

[Taylortwocities]

Hmph. Obviously i need to get a PhD in an ology.
I was working on the same principle as in plumbing. If the article in the link is correct, you wouldn’t need larger pipes at the supply end and smaller pipes at the delivery end. You could just have 15mm pipes into everybody’s house straight off a 200mm mains pipe.

And, if air ducting is different, let’s just use a 5mm dia straw off the 125mm fan. Nah, there’ll be a loss in air throughput.

 

[Cocat2517]

Aside from the performance issues, it will make more noise, I guarantee you. That would be enough for me to not do it.

What, using 100mm ducting on a 125mm fan as opposed to 125mm ducting will be noisier, or an inline fan in general will be noisier than a standard extractor?

 

[Cocat2517]

I'll have a flick through that article, but I'll fit it expecting some loss in performance. I'm going to be lazy and just use existing 100mm ducting and fingers crossed it'll suffice for the job. Ducting us cheap enough, so worse case scenario I'll have to pick some up and replace the 100mm. Thanks for all the replies.

 

[rsgaz]

What, using 100mm ducting on a 125mm fan as opposed to 125mm ducting will be noisier,

Yes.

 

[Cocat2517]

Yes.

Ok, thanks. I'll see what it's like once fitted and swap to 125mm later if it's an issue. Cheers.