When you say "exhaust vents in your ceiling" I assume you are referriong to the heating and AC vents inside your house and not the roof vent on the outside used to vent the attic. It is most likely that the duct work was ran in the ceiling for ease of installtion or the house may be built on a slab and they did not want to run the duct work through the slab.
Thanks for answering the question Should ceiling vents be directed towards the window or the room? NOT
on the floor on the floor
should be on floor.
The purpose of Ceiling Vents is to provide Ventilation in a room where it may be necessary, such as a Science Lab. Because gases generally rise (as they are hotter than the air and so less dense), they can escape out of the ceiling vents without causing any harm to people inside the science lab. They can also be used to help deal with a fire.
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.
Having the ceiling fan blow upwards will circulate the heat through the entire room.
Heat and condensation
Cose the high vents in the winter and low in the summer..
Ceiling. Cold air fails
Does not matter. Air will displace naturally when pushed into a room from the vent. Vents and ducting are laid out according to the plans of the unit. That is the only reason for top vents and bottom vents. If you are speaking of the intakes, the same principal applies.
Probably around the heat/AC vents. Moisture can settle in and around the vents from condensation and turn into a breeding ground for bacteria. Often the vents are in the ceiling and get overlooked during cleaning.
It is recommended that you have both intake vents and exhaust vents. Most do it yourself sites recommend soffit vents for the intakes. Exhaust vents vary in both type and cost. For smaller houses the most recommended type is a ridge vent system. The number you will need depends on the square footage of your attic.