AC Running But House Still Humid: What's Wrong
Air conditioning should dehumidify, but sometimes the house stays sticky even when cool. Here's why and how to address it.
You set the thermostat lower, the house cools down, but it still feels clammy and humid. Your AC should be removing moisture—why isn't it?
How AC Removes Humidity
Air conditioners dehumidify as a byproduct of cooling. Warm, humid air passes over the cold evaporator coil. Moisture condenses and drains away. The drier air returns to your rooms.
Why Humidity Stays High
Oversized AC This is a common cause. An oversized unit: - Cools the space quickly - Shuts off before running long enough to dehumidify - Results in short cycles that don't remove moisture
Unfortunately, the fix is replacing with correctly sized equipment.
Short Cycling Even with properly sized equipment, short cycling due to other issues (thermostat location, refrigerant problems) reduces dehumidification.
Fan Set to ON Instead of AUTO When the fan runs continuously, moisture on the coil re-evaporates back into the air between cooling cycles.
Coil or Drainage Issues A dirty evaporator coil or poor condensate drainage reduces dehumidification capacity.
Leaky Ductwork If ducts in humid spaces (attics, crawlspaces) have leaks, humid air infiltrates the system.
Home Air Leaks If outdoor humid air enters faster than your AC can dehumidify, humidity stays high.
Single-Stage Equipment Single-stage systems running at full capacity cycle off quickly. Variable-speed systems can run longer at lower capacity, improving dehumidification.
Solutions
Quick Fixes - Set the fan to AUTO, not ON - Check for coil and drainage issues
System Improvements - Address air leaks in the home envelope - Seal ductwork - Consider a whole-house dehumidifier
Equipment Options - Variable-speed equipment dehumidifies better - Some systems have enhanced dehumidification modes - Whole-house dehumidifiers work independently of cooling
Bay Area Considerations
The Bay Area has moderate humidity most of the year. If humidity is a problem: - Check if coastal fog is raising humidity during certain times - Ensure bathroom and kitchen exhaust fans vent outside - Consider a dehumidifier for problem seasons