Gap Under Bathroom Door For Ventilation

If your door has very little or no clearance at the bottom you.
Gap under bathroom door for ventilation. I think it is too big and think a 1 4 1 2 gap would accommodate any unevenness in our floors and allow us to use area rugs. However the size of that gap is very unlikely to be greater than 1 2 for any door. And for proper bathroom ventilation your exhaust fan needs to vent outside not into the attic or another area of the house. If the bathroom vent can t get any air of course it isn t going to work the right way.
My mom has a house with a central return and as you suggest her doors have about a 1 5 gap underneath to allow air to flow. I have a problem with the door vents you are passively promoting. This is less than desirable in bathrooms and bedrooms. There is an approximately 1 5 gap at the bottom of the doors.
There is a need for an air gap at the bottom for ventilation. Using the link you have provided it has a picture of a french full lite door with a vent that has removed a significant part of the door s base. The flow dropped from an unrestricted 150 160 cfm down to under 100 cfm in each room. Client always resist 1 gap over the floor covering.
There should be plenty of room under the bottom of the bathroom door to allow air to get into the room so the fan has a source from which to pull the air it needs. I like the suggestions for wall ceiling jump ducts etc. The jumper makes sense in some cases. Check your bathroom door.