Hi,

Mark Reker 4336 Flowerfield. 

I am athe neighbor Dan Wagner referenced.

While I have had limited success, and currently not attempting to us, with the method Dan describes my suspicion is a the number of cold air vents in the lower level is a key factor. 

My lower level vents are:

1. At the bottom of the steps to left of the sliding patio door.

2. In the lower level bedroom on the left wall just past the bedroom door.

3. In the family room on the wall under the steps.

4. On the right wall just before entering the mechanical room.

My son was attempting something similar with his house and HVAC contractor suggested leaving the mechanical room door open which I also did.

Another of my suspicions is the fan speed setting for Fan Only - it might be possible for that to be internally set to a higher speed internal in the HVAC system.

To Dan's point about checking the temperature in the bath room vent - I used a meat thermometer to check temp WITH the Upper/Lower Fan ON and WITHOUT the Upper/Lower Fan OFF and you will quickly observe a several degree higher temp once Upper/Lower Fan is ON.

To the Dave H point about "dual zone (independent) systems".  There is only HVAC fan with the air in the Upper and Lower level ducts controlled by electronic dampers.  Once the Upper and Lower level Fans are on, it is then effectively one integrated system of ducts.  That said, the air flow may very likely not be evenly distributed to the two levels.

I just finished an experiment.  Turned both zones off for Cool/Heat.  Then turned both fan settings to On.  All of the cold air returns, upper and lower levels were pulling air.  Only the upper level was pushing air through the cool/heat vents.  Then I set the lower fan setting to Auto and left the upper fan setting to On and it behaved the same as when the lower level fan was On.  Finally, set the upper fan setting to Auto and lower fan setting to On, and only the lower level cool/heat vents were pushing air.  So, my point is that with a dual zone system, you can't have air pushed through both the upper and lower cool/heat vents at the same time.  However, the cold air return is not part of that system, in the sense that any time the furnace fan is running, it is pulling air from both levels.  So, having the upper fan control set to On will pull cooler air from the lower level, but it will mix with the warmer air from the upper level.  Not sure that's a significant benefit.  We've had better results placing a floor fan at the bottom of the stairs and pushing air up to the upper level.