2 questions about air vents in walls, cold draughts!

[D1nhs]

Hello! Its getting damn cold, and im begining to notice more cold draughts in the house.

1- We have a extractor hood in the kitchen and the ventilation pipe which is round is fed to a rectangular vent between the joist upstairs. We recently had carpet fitted and when the carpet was up i noticed a cold draught coming through the floorboards.

My questions is can i buy a one way vent that can be placed outside so the air from the extractor can flow out but no cold air in when the extractor isnt being used?

2- In the 3rd bedroom, there is a silver vent which when removed exposes a large cavity in the wall which on the other side has a outdoor grill/vent.

This room is really cold, even with the heating on max. My second question is, why is this vent there? there isnt any vents like this in any other room? Can i block it up, if so what would be the best way?

 

[big-all]

this sort of thing!!!
http://www.screwfix.com/prods/18561/Heating-Cooling/Ducting/Duct-Outlet-Flaps-White
and in the bedroom
if you have lots of draughts and assuming you have no gas appliances in that or the next room then yes you can seal up the vent "temporeraly"

eventualy as you seal up the windows floorboards and doors you will have to re-open the vents to stop condensation and mould

 

[foxhole]

I would'nt remove ventilation, only causes more problems especially in winter.