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Upstate South Carolina summers mean high humidity — anyone who’s lived through a July in Greenville or Spartanburg knows the feeling of walking into a house that’s technically at 72°F but feels like a damp cave. Our technician Gage sees this complaint spike every June as humidity climbs into the 70-80% range outside. The AC is running, the temperature reads right, but something feels wrong. Here’s what’s actually happening.
How Your AC Removes Humidity
When warm, humid air passes over the cold evaporator coil, moisture condenses on the coil surface (like a cold glass sweating on a summer day). That moisture drips into the drain pan and exits through the condensate line. This dehumidification is a natural part of the cooling process – not a separate function.
The key factor is run time. Your AC removes the most moisture during long, steady cooling cycles. Short cycles don’t give the coil enough time to pull meaningful moisture from the air.
Why It’s Not Enough
Oversized AC System
This is the most common cause of poor humidity control, and it’s a design problem, not a maintenance issue. An oversized AC cools the air temperature quickly but shuts off before removing adequate moisture. The result: the house reaches 72°F but feels like 78°F because the humidity is still 65%+.
An oversized system short-cycles – frequent on/off cycles of 5-10 minutes each. A properly sized system runs longer cycles (15-20+ minutes), removing more moisture per cycle.
If your system has always had this problem since installation, it may be oversized. A Manual J load calculation can confirm.
Fan Set to ON Instead of AUTO
When the fan runs continuously (ON setting), it blows air across the wet evaporator coil even when the compressor is off, re-evaporating moisture back into the air. Set the fan to AUTO so it only runs during active cooling cycles.
Leaky Ductwork
Duct leaks in the attic or crawlspace pull humid unconditioned air into the system. This introduces moisture faster than the AC can remove it, creating a never-ending humidity battle.
Inadequate Ventilation
Bathrooms and kitchens generate significant moisture. If exhaust fans are undersized, not ducted to the exterior (venting into the attic is a common code violation), or not used consistently, that moisture accumulates in the home.
Building Envelope Issues
Air leaks around windows, doors, electrical outlets, and pipe penetrations allow humid outdoor air to infiltrate the home. The tighter the building envelope, the easier it is to control indoor humidity.
Solutions
Whole-home dehumidifier: The most effective solution. Installed in the ductwork, it removes moisture independently of the AC system. It maintains a consistent humidity level (we recommend 45-50%) regardless of cooling demand. Cost: $1,500-$2,500 installed.
Variable-speed HVAC system: Variable-speed compressors and blower motors run at lower speeds for longer periods, providing superior dehumidification compared to single-speed systems that cycle on and off. This is the best option if you’re replacing your AC anyway.
Seal ductwork and air leaks: Addressing the source of excess moisture infiltration. Duct sealing and air sealing are among the highest-ROI home improvements for comfort and energy efficiency.
Use exhaust fans properly: Run bathroom exhaust fans during and for 15 minutes after showers. Run the kitchen exhaust when cooking. Verify fans are ducted to the exterior.
The Comfort Connection
Humidity has a larger impact on perceived comfort than temperature. At 50% humidity, 74°F feels comfortable. At 70% humidity, 74°F feels stuffy and warm. Controlling humidity often means you can set the thermostat higher and still feel comfortable – saving energy in the process.
YOUTUBE EMBED: One Drain – Waldrop Plumbing Air Electric TV Commercial — @YallCallWally
Call Waldrop Plumbing Air Electric at (864) 536-0887 to discuss humidity control options for your home.
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