Avoiding kitchen duct noise

[MJNewton]

My understanding, from Table 5.1a of Approved Document F, is that with MVHR a kitchen should have an extract rate of 13 L/s under boost. With the commonly-used 63mm ID flexible ducting this means a duct airflow speed of 4.17 m/s (if my maths is correct!) if only a single duct is used. Is this what others have done, or have you all doubled-up to avoid noise which I understand can become noticeable above 2.5 m/s?

Edited February 16, 2019 by MJNewton

[ProDave]

I used 2 63mm ducts to all my vents.

[Jeremy Harris]

I doubled up on the run to the kitchen extract, to get the flow velocity down.  It's silent except when running at full boost, when it makes a slight noise, but not anywhere near as loud as an extractor fan.