Learn why indoor humidity can remain high while the air conditioner is running, including equipment sizing, airflow, run time, duct leakage and moisture-source conditions.
Air conditioning removes both sensible heat and moisture, but dehumidification depends on coil temperature, airflow and how long the system runs.
A home can reach the thermostat setpoint quickly while still feeling damp if the system does not operate long enough for effective moisture removal.
Not every humidity problem is caused by the HVAC equipment. Building leakage, ventilation, groundwater, plumbing leaks and occupant moisture can also matter.
Excessive capacity can satisfy temperature quickly and reduce dehumidification run time.
High airflow across the evaporator can reduce moisture removal under some conditions.
Leaky return ducts can draw humid air from attics, crawlspaces or other unconditioned areas.
Aggressive setbacks and short cycles can affect humidity control.
Basement, crawlspace, plumbing or envelope conditions may be adding moisture faster than the AC can remove it.
Coil temperature, refrigerant conditions or other faults can reduce normal latent capacity.
Several different HVAC faults can produce the same homeowner symptom. Proper diagnosis may require electrical readings, refrigerant measurements, airflow testing, static-pressure measurements, combustion testing or control-sequence checks.
Do not bypass safeties, open sealed refrigerant circuits, work on gas piping or perform live electrical troubleshooting unless you are qualified to do so.
Short run times can reduce moisture removal.
Capacity problems can occur with humidity issues.
Incorrect airflow can affect cooling and humidity.
Understand humidity as part of the whole-home picture.
When requesting service, include the equipment type, approximate age, when the problem started, whether the system still operates and any unusual noise, water, odor or thermostat behavior you have noticed.
Use the IAQ Device Selector to compare practical options for filtration, air cleaning, humidity, moisture and ventilation—and see when an in-home evaluation makes more sense.
Understand temperature, relative humidity and dew point.
See how cooling and moisture removal are different loads.
Learn why oversized equipment can hurt humidity control.
Understand normal system operation before narrowing a symptom.