Why Your House Feels Clammy Even With the AC Running
Seventy two degrees and still sticky usually means a humidity problem, not a cooling problem. Often the air conditioner is the cause.
By Chris Wheeler, Co-owner ·
The thermostat says 72. The house feels like a basement. Somebody keeps turning it down and it just gets cold and clammy instead of comfortable.
That is a humidity problem, and it is common in older New Hampshire houses in August.
Comfort is temperature and moisture together
At 50 percent relative humidity, 75 degrees feels pleasant. At 70 percent, the same 75 degrees feels oppressive, because your sweat cannot evaporate and evaporation is how your body sheds heat.
Turning the thermostat down is the instinct and it is the wrong move. You end up in a cold, damp house, which is less comfortable than a slightly warmer dry one, and you pay more for it.
Target is roughly 45 to 55 percent in cooling season. A cheap hygrometer will tell you where you actually are, and it is worth the ten dollars before you spend anything else.
Why an oversized AC makes it worse
Here is the counterintuitive part. Your air conditioner is your primary dehumidifier, and an oversized one dehumidifies badly.
Moisture comes out of the air when it contacts the cold evaporator coil, condenses, and drains away. That takes time. The coil has to be cold and air has to keep passing over it for a sustained period.
An oversized system drops the air temperature to setpoint fast and shuts off. Short run times mean the coil barely gets going before it stops. You removed heat and left the moisture behind.
A correctly sized system runs longer at lower capacity, which is exactly the condition that pulls water out of the air. This is the single most common reason a house is cold and clammy, and the fix is not more capacity.
If your AC satisfies in short bursts and the house feels damp, the equipment is probably too big. There are things to do short of replacement, including slowing the blower speed and, on two stage or variable equipment, configuring it to favor longer low stage run times.
Other causes
Fan set to ON instead of AUTO. Very common and easy to fix. With the fan running continuously, the blower keeps moving air across a wet coil after the compressor shuts off, and that re evaporates moisture that had condensed and blows it right back into the house. Set the fan to AUTO.
Basement or crawlspace moisture. In an older house with a fieldstone or damp concrete basement, that space is a moisture source feeding the whole house. Damp earth floors and crawlspaces without vapor barriers put a lot of water into the air. Sealing and a vapor barrier down there often does more than anything you do upstairs.
Duct running through humid space. Cool air in leaky duct passing through a damp basement picks up moisture on the way to the room.
Ordinary household sources. Showers without an exhaust fan, cooking, laundry, a lot of houseplants. A bathroom fan that actually vents outdoors, and gets used, is not a small thing.
Ventilation running when it should not. If you have an ERV or fresh air intake, bringing in outdoor air on a humid August day brings the humidity with it.
The fix, in order of cost
- Set the fan to AUTO. Free.
- Measure. Ten dollar hygrometer.
- Use the bathroom and kitchen exhaust fans, and confirm they vent outside and not into the attic. We find fans dumping into attics regularly.
- Address basement or crawlspace moisture. Vapor barrier, sealing, sometimes a dedicated dehumidifier down there. Often the highest value item on this list in an older house.
- Adjust blower speed or staging on the existing equipment.
- A whole house dehumidifier tied into the duct system. This is the real answer for a house that is otherwise fine but runs humid, and it dehumidifies without overcooling.
- Right size the equipment at replacement time. Not worth replacing working equipment over, but when its time comes, do the load calculation.
What we will not tell you
We will not tell you that a bigger air conditioner will fix a clammy house. It is the opposite of the fix, and it is a common enough recommendation from people selling equipment that it is worth saying plainly.
If your house is cold and damp, call us and we will measure what is actually happening before anybody quotes anything.