Pascal

Almost none, honestly.

A pressure differential of just three to five Pascals, which is a minuscule amount of physical force, is enough to turn the gaps under your baseboards and the cracks around your window frames into high velocity cold air jets.

Wow.

By closing the door, the ballooning pressure in your bedroom forces your warm air out through the walls, and the vacuum in your living room sucks freezing cold air up from the basement.