I have a problem with the door vents you are passively promoting.
Gap under bathroom door for ventilation.
There is a need for an air gap at the bottom for ventilation.
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.
If the bathroom vent can t get any air of course it isn t going to work the right way.
There is an approximately 1 5 gap at the bottom of the doors.
I like the suggestions for wall ceiling jump ducts etc.
Client always resist 1 gap over the floor covering.
The flow dropped from an unrestricted 150 160 cfm down to under 100 cfm in each room.
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.
My contractor just hung our fancy dancy un painted solid wood door slabs in my 100 year old house with solid hardwood floors throughout.
A 10mm gap under the bathroom door is very usefull it allows the fan to work easier as it can draw in air and because its from within the house it stops the bathroom.
However the size of that gap is very unlikely to be greater than 1 2 for any door.
If more gap is required it is easier to trim a door than to lengthen it.
7 mistakes not to make in your bathroom remodel do let your.
The jumper makes sense in some cases.
Check your bathroom door.
This is less than desirable in bathrooms and bedrooms.
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.