I'm going to add some crown moulding to some bedrooms. I've got HVAC vents mounted near the top of the wall and the moulding will cover part of the vent.
I want to move the vents out of the way. I can't move them down and am thinking of moving them to the ceilings instead (there's an attic above them so I've got reasonable access). Is there any reason this is a bad plan? Do they work just as well in either location?
I think part of this depends on where you live, and whether this is primarily a cooling or a heating issue. I'll assume we are talking the high velocity vents, which are easy enough to move around. (A check of your profile says San Jose, so I also assume this is a cooling issue.)
Wall mounted vents used for cooling will push cool air across the ceiling, mixing with the warmer air up there. The cool air will now gradually settle down, because cool air is denser than warm air. What you won't feel so much is moving air.
Ceiling mounted vents, because they push the air DOWN, not horizontally, will arguably create more drafts in the volume that you actually inhabit. This is something my wife would not want. So if you do put them in the ceiling, place them where you will not feel the drafts.
In terms of new construction, I almost always see floor or ceiling mounted vents. The reason being that you need to build out the wall to be deep enough to run a vent into it. When it's in the ceiling, especially with todays joist designs, you can run large vent lines with plenty of insulation on them through the space between the ceiling and floor above. Most installations place the vents near windows and doors to counteract the drafts and reduced insulation at these locations, hopefully balancing the temperature in the room/home. That said, I think woodchips makes a great point that you want cooling air to stay high and heating to stay low if you ignore the doors and windows in this equation.
Typically, I only see horizontal vents in locations that have high ceilings (via the floor of an overlook or ceiling of an adjacent room), adjoining some kind of crawl space or utility room, or where the ceiling is bumped down to enclose the vent (because the joists were not designed to allow HVAC lines to pass through).
