A bit of both eh? My friend up north has those whirly gig things on the roof that spin around, drawing air out. He says they can be closed to trap warm air in but it has to be done manually..
So I think he has five each with 2 of those vents except one has three on it so that's about 11 vents that have to manually be shut at night or in cold weather
I think I can see the benefit to automation!
I have read that there are vent opener/closers that operate on temperature and hydraulics and don't need electrcity or batteries- they sound good to me
