Home HVAC Question

I live in a realtively small, 1.5 story (the upper floor is a loft is only about 1/2 as big as the ground floor) condo/townhouse. The main heating cooling duct runs between foors and thus has vents in the ceiling on the ground floor, and vents in the floor on the second level. The problem with the A/C is that I can keep the ground floor relatively cool but the upstairs is hot. There is plenty of cold air coming out of the floor vents upstairs, but the cold air just sinks to the floor and doesn’t circulate. The obvious answer, I guess, would just be a fan.

Questions are:

  1. Is this the best answer, or should my HVAC sysem be performing better?
  2. Is there a certain kind of fan I can get that would maximize lifting/circulating this cold air?
  3. Do they make special fans where the intake would be angled down and the approx size of a floor vent? And blow the air horizontally? I realize I could lay any fan on its back over the vent, but then it would just blow the air straight up.
  4. Any thing I’m not thinking of?

BTW, I have the exact opposite problem in the winter with the heat.


Had the same problem when I lived in a loft. What I did was get one of those Vortec style fans that can be angle to blow straight up and placed it in a corner on the low setting. That was enough to get the air mixing good and I saw no change in my electric bill.

You could also try shutting off (or slightly closing) some of the vents going into the lower rooms, that will force air to vent out of the top.

I’d second this one too. It sounds like they just slapped the ductwork into the wall without balancing any of the CFMs to the rooms, or taking into account convection. Either that, or you have a source of heat upstairs that they didn’t figure in. Got any skylights?

Either way, I’d agree with Si Amigo. Try shutting one or two of the vents in more out of the way places. That’ll direct some more air upstairs and hopefully push “more cold” where it needs to be. If you put a fan near the staircase, I’m afraid that would only speed up convection, and just push more air upstairs–bringing all that “more cold” downstairs and defeating the purpose.

Give 'er a shot.

There are fans called register boosters that are made for that. They blow up, not horizontally, but that’s what you want to do - mix the air vertically.

Thanks yoyodyne. That’s exactly what I’m looking for, didn’t know what they were called so it was hard to Google.

Si Amigo/Tripler: I’ve already closed off vents in all the rooms downstairs I’m not using and “sealed” them (well, towels under the doors) to prevent as much cold leakage as possible into those rooms. These are in the back of the unit, as well as the loft. What sucks about the floor plan layout is the loft is essentially over the living room and looks out over the Dining Room/Foyer/Entrance way (or whatever you would call it, approximatley 10’ X 10’ with a 2 story ceiling), which is essentially one big room with the living room. There is no way to seal off that wasted space.

No skylights but both rooms upstairs (loft, bedroom) have large sliding glass doors. These are a slight source of heat, but with curtains and all aren’t too bad.

If you have a single duct supplying both upstairs and downstairs, then this might not help, but some systems have louvers in the ducts leading away from the A/C unit to allow you to tune the volume of air in different destinations. Do you see things that look like levers on the side of any ducts near where they come of the the A/C unit?

I’ll have to check this when I get home, but all my duct work is incased in the walls/ceiling/wallboard (I think). This is very unlike the house I grew up in, where the furnace was in the basement and there was a myriad of metal ducting running all over the basement ceiling then up into the walls. This is a single duct running the centerline of my unit, between the downstairs ceiling and upstairs floor. The heating/AC unit is located along the centerline, behind a wall on the ground floor, and (I believe) there is just the main duct that runs straight (front to back) and all the vents are off it.

With a forced air system you’ll have a return air register, to return the air to the heating/cooling unit. This should be located in the loft area and may have a filter that needs changing, or it could be blocked, by furniture or something. That would cause you to not have proper air circulation, assuming the system was properly designed.
Do you have a ceiling light fixture? If so, it could be replaced w/ a ceiling fan/light combo. That could help circulation and they are asthetically pleasing. A ceiling fan could also save you money as you may not always need the A/C if you can circulate air w/ the fan on those, not to hot, days.

I’ve gotten better results with my air conditioner by switching the fan from “auto” to “on”. The fan uses slightly more electricity, because it runs all the time, and not just when the AC is running, but I’ve been able to raise the setpoint and still be comfortable, because I don’t have that upstairs/downstairs temperature gradient you speak of, so it’s a net savings.