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Apologies if this is a silly question but I can't find anything regarding the use of differing duct sizes on the site. The majority of rooms in our house require a single run of concealed 75mm semi rigid duct to satisfy building reg extract rates whilst keeping velocity low enough to minimise noise - at least in theory. Our kitchen/lounge/diner is larger and has a vaulted ceiling with a volume of 214m3 which is considerably more than anywhere else in the build. My calculations show the room needing 150mm diameter (or similar) ducts. This isn't an issue as we plan to use exposed galvanised in this space however I'm a little unsure if it is OK to mix duct sizes on a system or will it cause problems? Flow velocity at the outlets can be balanced in theory to within 1/2ms of other but the smaller rooms have an ACH of 2-3 whereas the largest room is 0.4. Is having such a varying range for this also an issue? Many thanks
