Said It Here

Why is my AC not lowering indoor humidity?

An air conditioner that cools the house too quickly or is oversized will shut off before it has run long enough to pull moisture out of the air. This leaves indoor humidity stuck above 60 percent, which creates the conditions for mold to grow around the house within a few months.

Overview
People affected23 accounts across 4 forums
Workarounds found45 items attempted
Community agreement63 total upvotes

What the numbers show

Counted from the threads quoted below. How we count

  • The most recent one is from October 2026.
  • This comes up 20.1× more often in r/hvacadvice than across the site as a whole.

What people tried

Every workaround mentioned in the threads below. We haven’t tested any of them — and nobody here is claiming they worked.

45 items+ Contribute

Found another way around this?

Share your steps and trade-offs so fellow engineers don't have to reinvent the wheel. No account required.

  1. 1
    running dehumidifiers
    Did this help you?
  2. 2
    dropping the system setpoint to force longer cooling cycles
    Did this help you?
  3. 3
    Retaping the plenum box
    Did this help you?
  4. 4
    Using a humidifier (or dehumidifier) downstairs
    Did this help you?
  5. 5
    Bought multiple hygrometers to monitor humidity levels
    Did this help you?
  6. 6
    Set up a portable Midea dehumidifier
    Did this help you?
  7. 7
    Had an HVAC company inspect the units
    Did this help you?
  8. 8
    Consulted ChatGPT for advice on air quality specialists
    Did this help you?
  9. 9
    Opening the apartment window for 30 minutes a day
    Did this help you?
  10. 10
    Running an air conditioner or bathroom vent
    Did this help you?
  11. 11
    Using a countertop dehumidifier with a continuous drain into a sink or bathtub
    Did this help you?
  12. 12
    Opening windows on a dry afternoon to temporarily drop humidity
    Did this help you?
  13. 13
    Tracking dewpoint instead of relative humidity
    Did this help you?
  14. 14
    Compiling a list of specific measurements for the technician to check
    Did this help you?
  15. 15
    Opening windows and running fans for a cross breeze at night and running dehumidifiers during the day
    Did this help you?
  16. 16
    Cracking just one or two windows in the room you are in with a fan blowing outwards
    Did this help you?
  17. 17
    Using a portable AC unit that vents out a window
    Did this help you?
  18. 18
    Turning off bathroom exhaust fans to prevent pulling in humid outside air
    Did this help you?
  19. 19
    Running the air conditioner
    Did this help you?
  20. 20
    Waiting for heating season to naturally drop humidity
    Did this help you?
  21. 21
    Using dehumidifiers with continuous drains
    Did this help you?
  22. 22
    Suggesting a mini split added to the second story to dehumidify and cool the area.
    Did this help you?
  23. 23
    buying portable dehumidifiers
    Did this help you?
  24. 24
    running heating and air conditioning at the same time
    Did this help you?
  25. 25
    Using a separate dehumidifier
    Did this help you?
  26. 26
    Leaving the window open to ventilate
    Did this help you?
  27. 27
    Experimenting with window positioning and fans
    Did this help you?
  28. 28
    Lowering the fan speed
    Did this help you?
  29. 29
    Using a smart thermostat to set minimum run times and increase cycle time
    Did this help you?
  30. 30
    Running a large dehumidifier
    Did this help you?
  31. 31
    Turning off the humidifier control and water supply line
    Did this help you?
  32. 32
    Contacting an HVAC professional or mold abatement company
    Did this help you?
  33. 33
    Using a portable dehumidifier
    Did this help you?
  34. 34
    Upgrading to a thermostat with dehumidification mode
    Did this help you?
  35. 35
    Relying on HVAC cooling to lower humidity when active
    Did this help you?
  36. 36
    Adjusting the crawlspace dehumidifier to be more aggressive
    Did this help you?
  37. 37
    Using an infrared camera to check for cool spots representing moisture
    Did this help you?
  38. 38
    Configuring the thermostat to run the AC fan during dehumidifier calls
    Did this help you?
  39. 39
    Accepting higher humidity levels than the desired target
    Did this help you?
  40. 40
    Switching the thermostat fan setting from ON to AUTO
    Did this help you?
  41. 41
    Cleaning AC coils
    Did this help you?
  42. 42
    Checking and clearing clogs in the condensate drain line
    Did this help you?
  43. 43
    Adjusting blower speed or checking refrigerant charge
    Did this help you?
  44. 44
    buying and installing a standalone dehumidifier
    Did this help you?
  45. 45
    improving exterior drainage with gutters and grading
    Did this help you?
Tried another approach not listed above?+ Share your workaround ↑

In their words

Unedited, grouped by where they were said, most upvoted first within each place, each linked to the thread it came from.

r/HomeMaintenance1 person · September 2026

“Am running two dehumidifiers with the bathroom exhaust fan on, all windows closed, but the in home humidity refuses to go below 60%.”source ↗

pottyjohnsmoker · r/HomeMaintenance · 15 upvotes
r/hvacadvice18 people · September 2026 – October 2026

“New HVAC install, house humidity went from 55% to 65% and won't come down. What do I make them check?”source ↗

“House used to sit at 55% RH or lower. Now it's stuck at 65%, spikes to 73%.”source ↗

“Nothing in my house is pulling moisture out.”source ↗

Any-Adagio8638 · r/hvacadvice · 13 upvotes

“I ran large dehumidifier seemed to help but I started noticing my houses humidity is just generally always high like 60%.”source ↗

“Now after this nor'easter I took the trash out and noticed 2 lines of black mold behind trash cans in garage running all the way up the wall.”source ↗

“I noticed some mold inside the humidifier in the basement, this should be off along with the water line but I'm wondering if the needle valve isn't working.”source ↗

Lithuanianfury · r/hvacadvice · 8 upvotes

“Now that we have been cooling for 4 months we started noticing mold around the house.”source ↗

“It’s been 4 days and humidity levels are still averaging in the mid 60%.”source ↗

Accurate_Degree_4725 · r/hvacadvice · 4 upvotes

“The unit cools the space and cycles off before any dehumidifying happens.”source ↗

stopdrpnro · r/hvacadvice · 2 upvotes

“During spring and fall (shoulder seasons), our house gets very humid with average reading of 60-68. Outdoor temps are mild, so neither heating nor cooling runs often.”source ↗

imdoc22 · r/hvacadvice · 2 upvotes

“immediately after it was done the humidity in my entire house started to rise. My house was pretty much 50% or below, but now it's 60% and up.”source ↗

“My fear is that my house is "too tight" now and that the only way to fix this is a whole home dehumidifier, the opposite effect I was hoping for.”source ↗

Strangemediator · r/hvacadvice · 2 upvotes

“I want to get my home humidity levels down, my unit can’t keep it below 60%.”source ↗

guywholikesplants · r/hvacadvice · 1 upvotes

“I am back. And it feels awful in my home right now.”source ↗

“Today I woke up and noticed the musty smell was back and it was humid/damp feeling both up and downstairs.”source ↗

“The whole house is between 71 and 80 % humidity depending on the thermostat vs the actual humidifier.”source ↗

“This thing is only a year old so I feel at my wits end”source ↗

ClapityTrapity · r/hvacadvice · 1 upvotes

“I also want to add that the doors have swelled so much they are not closing. (For atleast 2 rooms and the front door)”source ↗

ClapityTrapity · r/hvacadvice · 1 upvotes

“Recently we found several clothing items in our master bedroom closet with mold/mildew on them.”source ↗

“Reading up to 85% at time in the house (we live in the southeast U.S. and heat and humidity has been extremely high for weeks)”source ↗

“Got a midea de-humidifier set up and it’s keeping it around 65% RH.”source ↗

KCBB47 · r/hvacadvice · 1 upvotes

“Whenever I come back from work, I can feel the air has moist smell.”source ↗

“What would be best way to fix the issue without breaking the bank and without installing portable room dehumidifier?”source ↗

ProConXol_Consult · r/hvacadvice · 1 upvotes

“Since it's had tenants in, they've had significant increases in humidity (including moisture detectable on walls); an issue we never had.”source ↗

“While they say they're running the unit, they're also complaining about the power bill”source ↗

ATLien_3000 · r/hvacadvice · 1 upvotes

“Is it ok to run my heat so I can run my ac to dehumidify my house that’s at 67 percent humidity”source ↗

Maximum_Ad1298 · r/hvacadvice · 1 upvotes

“Tenants complaining that AC, which is set on 72, feels hot today (cause it’s in the lower 60s outside) but it normally feels cool (when it’s in the 80s outside). 🤷‍♂️”source ↗

markjack101 · r/hvacadvice · 1 upvotes

“Fighting the same issue. Two people with a ΔT of 19 and it’s 66 in their unit”source ↗

Cheap-Key-6132 · r/hvacadvice · 1 upvotes

“Humidity is lower in the house when the ac runs all day. Now with lower outdoor temps it doesn’t run nearly as much and humidity in the house rises.”source ↗

Suitable_Ad2602 · r/hvacadvice · 1 upvotes

“Humidity levels have increase in our house. I had a temp/humidity meter in our house to check temp for baby and it was always around 40% and never had any issues with humidity with the older system.”source ↗

“Now the levels are around 48-52% constantly even on dry days. When we wake up the temp isn't necessarily bad but we can feel the humidity in our house.”source ↗

“Also the new AC system turns on/off alot more but stays on shorter. So maybe it's working too well or overpowered?”source ↗

brightcoconut097 · r/hvacadvice · 1 upvotes

“House is cooling but feels pretty humid.”source ↗

“unsure where / if I have an air handler or if its an all in one.”source ↗

“Havent had an issue in two years so curious whats changed and how to fix it.”source ↗

hobieNE · r/hvacadvice · 1 upvotes

“After indoor humidity reached 80–90% and caused mold, we hired an HVAC company to install a dehumidifier.”source ↗

“The dehumidifier has now run nonstop for four days with a 50% target. Humidity stays around 65–70%, with indoor temperatures of ~69°F.”source ↗

“Does this install look right, and should I expect this unit to get me to our target of 50% (or lower)?”source ↗

Whoneedskeyboard · r/hvacadvice
r/homeowners2 people · September 2026

“Apparently the humidity even when I don't cook is 66%. Is it worth buying one to remove these pests ?”source ↗

Finite8_ · r/homeowners · 2 upvotes

“there is just one big window in the whole apartment, the bathroom has a vent. I open that window 30 minutes a day. Maybe because I live at the 16th floor? no idea.”source ↗

Finite8_ · r/homeowners · 1 upvotes

“Moving to a new house i’m terrified of creating the same issue as every item I owned had to be thrown away unfortunately.”source ↗

“Outdoor humidity is 80% and raining but I can’t take the heat any longer.”source ↗

Life_Wonder7268 · r/homeowners
r/HomeImprovement2 people · October 2026

“Went in the crawl space and it’s very humid in there. No standing water, but a lot of moisture. The vapor barrier is in horrid condition, so we’ve had a couple contractors out, but they both have refused to quote for a new vapor barrier and insist on upselling us to a full encapsulation system.”source ↗

Vamp13yre · r/HomeImprovement · 1 upvotes

“I had mine encapsulated in July and the humidity is still at 72% ish. I don’t have any standing water or really even evidence of moisture. Not sure what to do about it. The whole basement is 70-80%.”source ↗

PracticalBit6383 · r/HomeImprovement · 1 upvotes

Where this came up

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