Duct from one room to another - flexible or rigid?

[DangerousD]

Hi all,

In an effort to draw clean air into the main bedroom from the side of the house less blighted by traffic pollution, we are considering running a vent from the spare room on the other side of the house to the main bedroom via the loft, and installing an extractor fan on the spare room end to periodically drive air through. We would then leave the window on its just cracked open setting in the spare room, to get fresh air in there.

This will involve about a 2-3m run through the loft, however, there is fibreglass loft insulation up there. My options are:

1) A rigid plastic 100mm ducting setup, although with several joints where pipes and fittings meet each other to make the trip. Presumably these will have to be sealed somehow;

2) A flexible vent, for which it should be possible to get one single piece for the whole run (but I am not sure how rugged/airtight these are, and the joints at the ends would still require sealing).

How worried should I be about drawing in glass fibres from the loft, and which setup is more likely to be safer from this point of view?

Thanks in advance.

 

[HERTS P&D]

You could always move?

Andy

 

[bernardgreen]

If the fan is in the spare room and pushing air into the duct then the pressure in the duct will ( almost certainly ) be higher than the pressure outside the duct so any leakage will be air coming out of the duct. Hence glass fibres will not be sucked into the duct by the fan running

 

[John D v2.0]

I have been researching a similar setup for similar reasons and to reduce our condensation problem.
Definitely rigid, or semi rigid. The flexible stuff would not move as much air die to the resistance and would be noisier.
To visualise it, imagine a river bed or a gutter even with fast flowing water. You want the smoothest possible ride for the water (air) so basically straight and smooth.
You can get calculators online for the resistance of fittings, even a right angle bend (imagine your river/gutter again) has a big effect
Hope this helps!

 

[Paulg31]

I'd go for the rigid duct. There'll be far less resistance to air flow and you won't risk the hose getting crushed or kinked in the loft.

 

[Doggit]

You want to use rigid ducting and you'll seal each joint with - oddly enough - duct tape.

But think about doing the job properly, and running the ducting through to an outside wall. If you take the feed from the spare room, you can't guarantee that you're getting fresh air from the outside window; you'll most likely take it from the hallway instead. You'd need to rig up a low power inline fan to draw the air from outside, and you'd need a grill on the outside to stop insects etc getting into the ducting. You're aiming to create a whole house ventilation system, on a one room scale, so investigate these, and see what parts you can get.