"The lowly vent cover: it is an innocuous thing, sitting there, an ugly grate of metal in your ceiling, floor or wall. They may seem like a trivial aesthetic concern to the untrained eye. Vent covers, however, are an essential component in your ventilation system, and your choice of vent covers, and how you use them, can prove to be the major difference in how comfortable your home is and how much you spend each much on your heating and cooling bill.
The function of a vent cover is to redirect the air flow from the ventilation system to where it is needed most. Thus, rooms that don't see much traffic should have the vent covers closed while rooms that really need heating or cooling should have the vents left open. This simple change in behavior can have a big impact on your comfort levels and can reduce your monthly expenses.
Even more than your ventilation habits, your choice of vent covers can have an effect on your experience. There are three primary types of vent covers that people commonly use today, each with their own advantages and disadvantages."