Bathroom extractor fan - undersized roof vent?

[garmcqui]

Hi all,

I put a 5” inline extractor fan (Manrose MF125T) in our main bathroom, with a 5” vent in the ceiling near shower. However it doesn’t seem to have a great airflow, certainly no better than the 4” fan in the en suite. Yes, there’s room below the door.

One reason may be that the the roof tile extractor vent only has a 4” spigot, so I had to use a reducer just before it. Would this be causing a significant issue, and would adding a 2nd roof tile vent beside this one help? Then I can use a Y splitter and have the 5” fan exhausting through two 4” vents.

Alternatively, anyone know where I can get a Marley mendip extractor vent with a 5” spigot?

Any thoughts welcome

 

[jj4091]

"Would this be causing a significant issue,"

No. Have you set the speed to high?

 

[oldbutnotdead]

Is it ducted? How long is the duct, how many bends in it, is it the nasty flexible stuff?

 

[garmcqui]

Is it ducted? How long is the duct, how many bends in it, is it the nasty flexible stuff?

It is the flexible stuff, but there’s less than 1m on each side of the fan.

 

[garmcqui]

"Would this be causing a significant issue,"

No. Have you set the speed to high?

Yea, on high speed. Thanks

 

[oldbutnotdead]

Cool. Have you had a look at the duct- is it kinked or full of fluff or birds nest? Thats the only significant choke point, you get better performance if all the duct is on the exhaust side but at the cost of more noise

 

[ericmark]

In the last house I had problems, in this house I don't and I at first could not work out why. Then it twigged, new house no gap bottom of cubical door only at top, old house gap both top and bottom. I realised it was the chimney effect, with a gap top and bottom all the steam/water vapour is transfer to the room, if either top or bottom of shower cubical sealed no chimney effect and room does not get as damp, or no cubical also does not transfer the moisture.

If you reduce the vapour into the room likely the existing is enough.

 

[jj4091]

Have you checked that the ducting has not split during installation? If you hold a sheet of A4 paper close to the vent does it suck it up?