A/C vents in floors?

JohnnieBMay 9, 2008

I have an older home (1927 rowhouse) that had central air conditioning installed in the 1980s but we are doing a major renovation that involves opening ceilings, walls, and floors and are replacing and completely re-working the AC. The ductwork formerly snaked all over the attic with vents in the second floor ceilings; we are converting the attic to living space and burying ducts in the walls and ceilings. We have hot water radiators so the ductwork is A/C only.

We had hoped the ductwork would be unobtrusive but what we didn't even think about was placement of the vents. The A/C subcontractor starting installing ductwork yesterday and it looks like he is running ducts under floors so the vents will be blowing cool air up from the floor. Aside from this seeming extremely inefficient, it's a concern with furniture placement (one of them is right where we were going to place a desk, in a room that doesn't have many furniture placement options!). Aren't A/C vents usually placed in the ceiling or high on a wall? I know our neighbors had a similar setup but their system was installed with minimal disruption to the house and they had fewer options. How often are A/C vents placed in floors? Does this make sense? Does it compromise the efficiency of the system?

I'm going to talk to our architect and general contractor about this--I'm not sure how well they have been coordinating with the A/C guy but I'm starting to think our architect did not at all provide well for the ductwork when drawing up the plans. (Placement of the air handling unit has been another issue, but I realize that's often problematic and it looks like it's something we're going to have to live with.)

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While I prefer them in the ceiling and I think they are more effective in the ceiling, I have seen them in the floor with no real issues (except obstruction). Most of the vents in my house are on the floor or low on the wall, and I don't have any real issues. I have a heat pump, though (so heating and cooling). Make sure you have plenty of return air (return grills).

    Bookmark   May 9, 2008 at 5:26PM
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Heat rises toward the ceiling, cold air settles toward the floor.

For better mixing everything works better with both SA & RA at or near the ceiling.

If there is low airflow there will not be an adequate heatload on the evaporator coil which greatly reduces heat removal capacity of the system.

When the Return air & supply air are both at the floor level with low airflow & inadequate SA throw, the cold air will merely recirculate across the floor & back to the cooling coil. That 'can be' a very inefficient situation.

Correct sizing of the duct system is very important.

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Here is a link that might be useful: Sizing Air Conditioning Systems & Ductwork Systems

    Bookmark   May 10, 2008 at 9:39AM
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CJ Mechanical of North jersey llc.

placement in the floor should have been discussed with the layout by you.floor registers are perfictly fine as long as cfm and size duct has been correctly sized for good velocity.a properly sized register/cfm will throw the air so many feet hence mix with the hot air @ the ceiling.Return MUST be located high when useing floor registers.placement in walls could add more duct work,elbows,lenght of pipe,more labor and less flow.This is the kind of stuff that should be discussed during the bidding process.

    Bookmark   May 10, 2008 at 1:56PM
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No HVAC tech here just a homeowner.

I have an older home that was designed for heat and AC but it was made with all supplies in the floors except in the living room where they are in opposite walls near the floor.

I would rather have cold air from the ceiling and hot air from the floor. Since you don't have to worry about heating from these vents I would try to get them from the ceiling.

That said my system works well. I think the thing with it is that there are air return ducts in every room(none in the bathroom) and in each hallway on each floor of my house. The rooms on the 2nd and 3rd floors have the returns near the ceiling and all large rooms have more than one return; one in the wall near the floor, the other in the wall near the ceiling. Also from what I can see and what my neighbors say, is that the supply ducts are large which allows plenty of air flow.

The outlets from the floor throw the air directly up into the room, not from side to side. This works well in the summer and winter. In the winter the living room that has the outlets in the wall blow the air in front of and across the outer wall which contains floor to ceiling(13FT) windows and french doors. In the summer I place directional louvers over these which direct the cold air up into the room.

Even though this works If I had a choice I still would rather have that cold air coming from the ceiling.

    Bookmark   May 11, 2008 at 12:01AM
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Thanks everybody, we are meeting with our architect & general contractor tomorrow morning to discuss this--our architect thinks the A/C guy misunderstood some of our discussions about ductwork (but I do wish they had all coordinated this better!). One of the most ludicrous was a floor register in the third floor bathroom. Hello??? Water???

We did know that one room, a sunporch on the back of the house, was problematic with regard to ductwork, and were expecting a floor register in that one room only as it could be fed by ductwork from the kitchen below (where we are dropping our 9' ceiling by 6" to accommodate the first floor ductwork).

I think that a big part of the problem is that during the planning stages our architect relied on the expertise and recommendations of an A/C person she has worked with before (and who did a great job with our neighbors' A/C), and we had planned on placing the air handling unit on the second floor. But our GC's A/C subcontractor had different ideas and insisted the AHU had to go on the third floor. I understand it would be more efficient that way, but is it absolutely necessary? Also, this places the AHU in a closet in our master bedroom, and we're concerned about noise when it is running--this was one of my initial objections to this placement, but they said they can soundproof it.

    Bookmark   May 11, 2008 at 10:37AM
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Bathroom register should definitely be located on the wall... or the ceiling. Good luck. Feel free to ask any more questions.

    Bookmark   May 11, 2008 at 8:11PM
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