Two Sets Air Returns; Which for A/C?

16 years ago

Forgive me for asking AGAIN. I promise to write it down this time.

We have floor supply and two sets of air return registers. Which registers should be open for cooling: The ones low on the wall or the ones high on the wall?

I have the low ones open now, but the humidity is still 50% in here. Perhaps the A/C units can't keep up with the 90-degree heat?

Single floor house w/unfinished basement. Gas forced air heat. Nine-foot ceilings. House (and HVAC systems) 10 years old.

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Comments (3)

chisue
Original Author
16 years ago
Oh, I think I may have found the reason for the high humidity by reading in another thread here.

I've had the blower 'ON'. Should only run the blower when I'm NOT running the A/C? (Fan should be left on 'Auto' when the A/C is running?)
creek_side
16 years ago
If you are short cycling (compressor in the outside unit runs for a short while, then shuts off, only to repeat after 10 to 15 minutes or less), then having the fan ON may cause the residual condensate to rehumidify the house.

If you are not short cycling (outside unit runs continuously for long periods) having the fan ON will have no material effect.

If your thermostat has a third position (not OFF) such as CIRC or something similar, use that setting. It will periodically run the fan, but not right after the compressor has run.
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chisue
Original Author
16 years ago
creek_side -- Thanks. No, it isn't short-cycling; runs steadily. Thermostat has fan choices of "Auto" or "On". "On" is same as the "circulate" you mentioned.

Thermostat offers "Hold" choice to raise or lower temp from the "Scheduled" setting.

Yesterday exterior temp was 90 and exterior humidity was also in the 90's. Interior scheduled setting was 77. I had the fan set at "On". It felt humid indoors. I set the thermostat to "Hold 74" and left the fan set at "On". In two hours the interior temp never dropped from 77 and the humidity was still 50%.

Still need answer about which air returns should be open for cooling -- uppers or lowers.