Does anyone know which would give me a smoother rectangular curve in a type space
My plan is to use a reducer to go from 200 -> 250 duct then make a rectangular template 300 x 90, put that inside the tube and deform about 50cm of tube into a rectangular shape, then pull it through the gap, then once out the soffit change about 20cm length into a gradual curve again and attach that to a vent.
PS (In case you suggest the following)...
You can buy a 220x90 mm rectanguar duct with adapter to 150mm, the problem is I can't get this into position, so it's not an option.
^ to get this device into position it would need to fit through a 150mm round hole in the soffit or a 350x100mm gap in the attic framing, which is not possible.