Hello,
I'm in the process of having a home built. In the model the heating vent is behind the bathroom door. Is this proper?

Should heating vents be placed behind a bathroom door?

Heating vents do the most good when placed on outside perimiter of the home; under windows, near doors. Behind the door will restrict it's efficiency, but I supect the layout didn't allow the vent to be where it should be. Tell the builder where you want it, or better yet consult a hvac engineer. It's your money.

MB is right on.

I've got one behind a bathroom door. Annoying, yes.