Had a couple of quotes for new windows - local firms - no pressure selling at all.
The exisiting windows don't have trickle vents.
Neither firm mentioned them until I asked.
Both said as the existing windows don't have vents - there's no building regs obligation to fit them on the new windows.
Both said they are very cheap to fit - about a tenner - but expensive to retro-fit.
One said some people complain about a draught.
One said drilling the frame compromises A- rating.
Otherwise neither put a case for or against.
What's the best thing to do? Are they an essential or not? Is opening windows better?