in the floor.
Heating vents should be placed near or on the floor in a room because heat travels up not down.
Heating vents should be located near the floor since hot air rises. If the heating vents are located near the ceiling the heat would stay there and not warm the room.
on the floor on the floor
Heating vents should be placed on or near the floor because heat rises. In rising, it will warm the air of the room. If the heating vent were near the ceiling, the room would stay chilly, even though heat was being poured into it.
Whatever it is set to on your heater's control keypad.
because warm air rises.
A ceiling fan should blow downwards when used with cooling, upward when used with heating.
In my opinion where the supply vents are located is not as important as where the return air vents are located. the supply vents should be located towards the outer walls if possible. the return air vents should be located towards the center of the dwelling if possible. every effort should be made to get the return air vents as high as possible on the wall , if not in the ceiling.Remember you are trying to get the warm air back to the a-coil so it can be pumped outside through the refrigeration lines to the condensing unit. if the ductwork is used for heating also you should put some return air vents down low to get the cool air to the furnace. This is my personal opinion and may not be everyones.
Vents should be cross ventilated in homes. This is an example sentence for vents.