My own going improving the standard of living in my house, I got a bathroom extractor fan properly installed (by a registered electrician and vented outside).

So this particular fan needs to have a air flow source to minimise the chance of it burning out trying to create a vacuum, standard approaches are to leave the bathroom door slightly open or a window, other people I have heard have shaved a bit off the bottom of the bathroom door to allow air flow.

What is the standard way for doing this?  Are vents sometime included from elsewhere in the house as an option, like through the wall to the hall (where there is a gas heater in my place).

Leaving the window cracked is OK in summer but not like mornings like this morning!