We all know the importance of ventilation, or at least we should. Healthy living means healthy accommodation, and includes ventilation. I know you might feel there is a contradiction here, with building regulations requiring air tight houses while at the same time ordering holes in the walls. But the point of having an air tight house is to allow some control over the ventilation and prevent the house leaking like a sieve, making it impossible to heat.
But human nature been what it is, we are inclined to close/block vents (and in fairness some cases in places of severe exposure, vents facing into prominent winds are problematic). Often on inspection I would advise people to open vents, which is unwanted advice. So a mitigating measure (but not complete solution) to allow at least some air change is to provide vents onto hallways, occasionally in older houses you will see vents over doors. It’s an effective way of reducing the draft under a door while at the same time providing cross ventilation in the house (regulation requirement for new builds). Been over head level you are less likely to feel a draft as you would feel from under a doorway.