I just moved into a new home and I live in hot, humid, Louisiana. We have two AC units, one upstairs and one downstairs. The unit upstairs has a dehumidifier but the one downstairs does not. I have the setting in the dehumidifier upstairs set to 50% per recommendations, but it cannot reach that level. This has the effect that the fan upstairs is always running. The thermostats are both Honeywell T10s, and I am assuming that only the upstairs unit has a dehumidifier because that's the only thermostat where I can change that option.

I have noticed two things, that downstairs it feels significantly cooler than upstairs even when both thermostats are reading the same temperature. The only way I could get the fan upstairs to finally turn off was when I changed the dehumidifier setting to 60% - 65%. I am worried that by leaving the humidity setting at 50%, the upstairs unit will never stop running and drive the unit to wear out quicker and my bill to skyrocket as a side effect.

Both AC units are brand new. Should I reach out to get the upstairs unit looked at? Is 50% humidity unrealistic for hot, humid Louisiana in June?

Thanks for your help!

1 Answer 1


All ac units dehumidify.

a dedicated dehumidifier is a ac unit that the hot air is returned into the room where ac the hot air is exhausted.

There are some AC models that are optimized to reduce humidity.

I have a wet bulb dry bulb humidity tester and I have heard your same issue in the past and found yes there is a difference and you can feel the difference with a change in humidity at the same temperature.

The difference I found was the ac units that are designed with dehumidification are quite a bit more expensive as they use active components (thermally controlled expansion valves verses cheap capillary tubes) the temps is controlled at a tighter level for moisture removal without freezing.

I doubt there is anything wrong with the upstairs system, being warmer upstairs will normally take much more run time. If both units are the same size swap them you will probably have the same result as the lower floor usually has less heat loading than an upper floor and that creates the difference that can be seen with a wet bulb dry bulb tester. Remember room size and heat loads can make a HUGE difference.

  • Great, thanks! So, should I just let it run constantly even though it has never reached 50%?
    – Jav Solo
    Jun 25, 2021 at 1:13
  • I don’t know the model but it may reduce the power once the temp is made. A kilowatt meter would be one way to measure the power used.
    – Ed Beal
    Jun 25, 2021 at 2:27
  • Can you post a picture or name and model number of the dehumidifier so we can be sure that it is what you say it is and is not a humidifier. Many times people mistake one for the other.
    – d.george
    Jun 25, 2021 at 11:00
  • @d.George the unit that is not getting the humidity low enough upstairs is an AC unit with dehumidifier settings according to OP.
    – Ed Beal
    Jun 25, 2021 at 13:06

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