Installing ducting

[gravelld]

I'm going to be installing ducting from three wet rooms (1 x kitchen, 2 x bathroom) and I wondered if there were any decent guides with best practice? It's just the ducting I'm interested in.

 

This is a retrofit in an occupied house.

 

The unit I'm fitting the ducting into is https://www.aereco.co.uk/products/exhaust-fans-uk/v4a-premium/

 

The unit will be in the cold loft. The kitchen is downstairs and the ducting will run through an airing cupboard. The bathrooms are both upstairs and the ducting will run directly from the outlets in the ceiling into the unit. The outlet from the unit will be into a roof vent.

 

Here's what I've found so far (some of this, e.g. the 125mm suggestion is from the manufacturer, Aereco):

 

- Insulate all ducts in cold space
- Try to have the same lengths of duct between rooms, but err on side of being closest to the kitchen duct

- Use 125mm duct
- If using flexible ducts, should be neither too loose or too taught, should just "hang natural"
- Condensation trap required on vertical discharges over 1m inside unheated space.
- Spend good money on proper tape (suggestions?) and also apply a mastic seal

 

Some things I'm not sure on:

 

- Flexible or rigid?

- Rectangular or circular?

- Should all runs be at right angles? (Up to the unit I guess, there's probably always a need for an angle there)

 

Any more? Any other pointers?

Edited March 18, 2020 by gravelld

[ProDave]

Do not let the runs "sag" or condensation may fill and block them. Keep them supported and level.

[matt_bag]

Agree with ProDave - keep your ducting taught and make the highest point of the system the fan unit - this will ensure any condensation runs away from the fan unit. I’d use flexible round insulated aluminium ducting for this installation. The ducting can run to the fan unit from any angle, right angles add resistance to the air flow equal to a theoretical Additional metre to your ducting length. The straighter the run can be to the unit the better - take the most direct route you can!

[gravelld]

Thanks, I had in my mind lots of right angles but it sounds like that's not the best way!