Should ac vents be placed in the ceiling or floor?

Answer 1

Either way will work ok as long as the system is designed that way from the beginning. The best place for the air conditioning registers (vents) will depend on who designs the system and the construction of your home. In some homes it is not practical to install the registers in the floor that have a concrete foundation. If you have a very low or flat roof it may not be practical to install them in the ceiling. Houses that are cooling most of the year have the registers in the ceiling and home that heat most of the year tend to have the registers in the floor.