I have a couple of ideas as to what these are there for, but I have vents in my ceilings that go to nowhere. They are in all the rooms, all of them go into the attic and are all connected to each other by regular ducting. But they don't exhaust anywhere.
I'm not exactly sure why they exist.
I'm thinking of two possibilities
1) They are from an aborted attempt at installing AC 2) They are for the purpose of dumping hot air into the attic.I'd always assumed that they all connected up with each other and routed back to the furnace, but the ducting literally goes nowhere - it's all contained in the attic and it's all SEALED - meaning there is no exit port.
What got me wondering about it was whether or not I should seal the vents during the winter to conserve heat.