Question re Placement of Ceiling Supply & Return Vents
This post is a question regarding placement of ceiling supply and return lines.
I'm building a new 2700 sq foot single story home in Central Florida (Lake County). The HVAC is a Lennox system with G60V gas furnace and XC21 A/C unit. The system will have four zones. Supply and Return vents / ducts / grilles are in the ceilings.
The builder's sub-contractor for HVAC has a general practice of putting the supply and return openings in each room in a location about 6" out from the wall and about 3' - 4' apart against the same wall. These are all placed over the inner walls, not over walls that have windows or doors. The placement is the same for a given model home, no matter what the home orientation is. In other words, a home with a Master Bedroom with windows facing south west will have the supply / returns in the same location as a home with the Master Bedroom windows facing north east.
My question - Is this a normal / good practice? Should I press the builder for the vents to be in other locations in the rooms?
I would think that there would be little airflow with the supply and return so close together and that the heat / cold from the window or door areas would not be properly conditioned.
Advice would be appreciated.
I'm interested in the answer to this question. My belief is that others here have said that what you describe is in fact the ideal placement.
IIRC, the idea is that the supply pushes the air from an interior wall to an exterior wall, washing that hotter exterior wall with cool air, which picks up heat that is then moved toward the return and back to the air handler.
I do not think that the placement of the supply and returns on the same wall would make that much of a difference. Try this take a match light it and hold it 12" away and try to suck it out then blow it out. See the difference the throw is going to be there when it comes to the supply.
Florida is primarily a cooling climate. Supply register placement along an interior wall with supply throw toward the outside walls is the way to go in a cooling climate, IMO. Manual T from ACCA supports this air pattern. Returns placed within 4' of a supply will not suck supply air over to it, due to a return having little large scale effect on air movement in a room. This is said with the understanding that the supply air is not being thrown toward the return, as might be possible with poorly aimed three-way supply registers.
For ceiling supply air entry points, the ideal approach would be to use a ceiling diffuser mounted in the center of the room that discharges air along the ceiling and throws the air in all directions toward the walls. Few residential installations are done this way. Most are as you describe, with a few registers appearing over windows and directing air back toward the room.
My personal preference for ceiling supply registers mounted near interior walls is to use adjustable curved blade registers to throw the supply air along the ceiling and toward the outside wall with windows. Windows are where most of the heat gain to a room comes from, followed by ceilings and walls. Washing exterior walls and windows keeps their surface temperatures lower, which translates to better rejection of body heat via radiation to those surfaces due to their lower temperatures.
In my own home I have installed single throw curved blade registers throughout the entire house, with all throws adjusted as described above. This was done right before the onset of the cooling season and now that it is here, one BIG benefit is a reduced complaint quotient from my wife regarding her personal comfort levels. She chills easily so any perceived draft sends her flying for a blanket or jacket. With the supply throws aimed so they do not intrude into the occupied zone, she has less chance of feeling a draft from the a/c system.
As for my own comfort levels, it's a home run. So far this spring I haven't needed a fan running at night to sleep. Used to be it ran all the time during cooling season.
Building Physics Rule #1: Hot flows to cold.
Building Physics Rule #2: Higher air pressure moves toward lower air pressure
Building Physics Rule #3: Higher moisture concentration moves toward lower moisture concentration.
Thanks for the fast response.
i read the manual. but to me the mechanics are still getting me lost. here is a picture of one of my rooms. note: these are on the interior wall on a house in jacksonville
Last edited by benglade; 05-22-2010 at 10:40 AM.
It depends on the throw of the supply grills. But we never put the return near the supply grills. We like for the air to be pulled across as much of the room area as possible.
so the vents should be further away than what is in the picture? or as long as the vents are facing toward the exterior that should be fine? Just wondering if i need to get the guy to move these things..
And Thanks Again
Not a problem ,as shophound's post is accurate.
Originally Posted by benglade
We are in Florida and have done thousands of homes this way, as do all contractors in Florida.
Sizing of ducts and grilles must be per ACCA's Manual D,if not you'll have issues regardless of grille location.
That helps alot.. just been up North to long i guess and just looked confusing..