Sticky house, AC running
Cooling and drying are two separate jobs, and a central AC does both at once. In a mid-Missouri summer the drying half carries as much weight as the cooling half. When the thermostat reads fine but the house feels clammy, look first at the fan switch, then at whether the unit is too big, then at outside air sneaking in.
The moisture Columbia hands your AC
The airport averages 41.42 inches of rain a year (1991-2020), and close to a third of it, 31%, arrives in May, June and July. By July the overnight low is averaging 69.2°F. Air that warm and that wet holds a heavy load of water vapor, and whatever finds its way indoors has to condense on the evaporator coil and run down the drain before the house feels dry.
Where the dampness usually comes from
- Fan switch on ON. When the blower keeps going after the compressor stops, moisture still clinging to the coil gets blown back into the rooms instead of dripping into the pan. Flip it to AUTO and give it a day. Free test.
- Too much tonnage. The DOE notes that an oversized unit removes humidity poorly: it drops the temperature quickly and stops before enough water has condensed out.
- Dirty coil or filter. Less air across the coil means less water pulled out of it.
- Leaky returns. A return duct with gaps in a crawlspace or attic sucks in outside air that is already muggy.
- Low charge. A system short on refrigerant often stops drying the air before it stops cooling it.
- An unconditioned basement. Below grade, a dedicated dehumidifier is often the right tool.
On the service visit
- Verify the refrigerant charge, and clean the indoor coil if it needs it.
- Measure airflow. Many air handlers have a slower blower setting meant for humid climates.
- Inspect the return side for leaks.
- Discuss a whole-house dehumidifier now, or a variable-speed system when it is time to replace, since long low-speed runs pull more water.
Shopping for a new unit? Getting the tonnage right will do more for a clammy house than any brand name. How sizing works.
What Boone County homeowners ask us
The AC is running. Why does the house still feel humid?
The fan left on ON, an oversized unit that short cycles, a dirty coil or filter, leaking return ducts, or a low charge are the common causes. Move the fan to AUTO before anything else.
Do I need a dehumidifier if I have central air?
In a damp basement, often. Upstairs, a properly sized and charged system should keep up on its own; if it doesn't, have a technician find out why before you buy more equipment.