Ventilation

Ventilation

This is the ductwork and the outside terminal rather than the powered unit, so it covers what an extractor fan or cooker hood connects to. Sizing starts at the appliance outlet and works outwards: match the duct to the diameter of the outlet and only reduce where the run genuinely demands it, because narrowing the duct restricts airflow and makes the unit work harder for less extraction. Reducers exist for the common mismatches, typically 125mm to 100mm and 150mm to 120mm between a cooker hood outlet and existing ductwork. Rigid duct moves air better than flexible, and flexible duct should be pulled taut rather than left concertinaed, because the ribbing creates turbulence that costs airflow with every metre. Every bend costs more, so plan the shortest sensible route and clip the run so it cannot sag. The outside terminal is chosen by what is behind it. Gravity vents use a flap that opens with the airflow and drops shut when the fan stops, which blocks draughts and is the right choice for anything fan driven. Hooded vents throw rain clear of the opening and suit exposed walls. Louvre vents are the fixed pattern for passive ventilation where air should always move, and adjustable vents do the same job but close off when you do not want the airflow. Round vents with a flyscreen keep insects out of the duct.

Powermaster supplies most of the range, covering 4 inch gravity wall vents in white and brown, 4 inch hooded vents in white and black, 4 inch PVC ducting in 3 metre lengths, 4 inch flexible PVC ducting in 6 metre lengths, 6 inch PVC ducting in 3 metre lengths and ducting clips in 2 packs at 4, 5 and 6 inch. Alongside these are louvre wall vents in white at 9 inch by 6 inch and 9 inch by 9 inch, an aluminium louvre vent at 9 inch by 6 inch, adjustable vents at both sizes, a fixed round wall vent at 145mm with a flyscreen, and cooker hood reducers from 125mm to 100mm and 150mm to 120mm. For the powered units themselves see Cooker Hoods and Air Purification.