Lumen

I see ? Thanks for heads up, I take it simple 100mm Non Return Valve should do the trick?

Pardon my ignorance, but what is T9?

Hello chaps! I'm looking to redo the air ventilation in the bathrooms, as we've are adding the 3rd shower room on the top floor (loft conversion). So the house setup would consist of: G-floor - clock room / loo (small 6 4" by 22 foot) - 16 feet from loft extractor 1-st floor (main) bathroom (6 4" x 6 4") 10 feet away form loft extractor 2nd floor new shower room (4 foot x 6 4") will be just ceiling high away form loft extractor. The inline extractor I'm planning to use is: Manrose MF100T (68 litres per second, 245 cubic metres per hour extraction on max) for all 3 bathrooms and balance the airflow using adjustable ceiling vents. The current air vents are solid galvanised steel 4" pipes which run from the ground floor loo and into the roof. Is that sufficient for extracting in those 3 locations. What else do I need to do while I have access? Condensation trap and insulate the air vent pipes? Any advise much appreciated. Lumen