Turning the thermostat down won't dry out a sticky Lake City house, and here is what will

The thermostat myth

Lake City believes, as most of humid Florida does, that a sticky house is a thermostat problem. Turn it down a few degrees and the dampness will go. It is an understandable belief, because the air conditioner does remove water as a side effect of cooling, and because for a few minutes after the setpoint drops, the long run that follows does dry the house a little. Then the system catches up, shuts off, and the humidity climbs right back while the house sits colder, the FPL or Clay Electric meter spins faster, and the sliding glass door fogs on the inside.

The thermostat measures temperature. The problem is water. Those are different quantities, and the fix for the second one is not more of the first.

What “sticky” means in numbers

Buy or borrow a hygrometer; they cost less than a filter. Put it on the coffee table for a day. In a Lake City summer, with the house cooling normally, a reading under 50 percent is dry and comfortable, and 74 will feel cool. Fifty-five is the upper edge of fine. Sixty is sticky, and the house will feel warmer than it is. Sixty-five and above is the range where mold grows on the back of closet walls, leather goes grey, wood swells and the air has that closed-up August smell by June. From June through September, when the daily thunderstorm resets the outdoor air to saturation every afternoon, most houses in this town that are not actively managing humidity sit at 60 or above.

Why Lake City houses stay damp: the ranked list

1. The system is too big for the house. A unit sized “to be safe” cools the air in a few minutes and stops before the coil has run long enough to remove water. The single largest cause in the 1990s-2000s subdivisions, and a common inheritance when a replacement matched the old tonnage.
2. The thermostat fan is set to ON. The coil is dripping wet at the end of each cooling cycle. A fan that keeps running blows room air across it and evaporates that water straight back into the house.
3. Return duct leaks in the attic. The return side of a 1970s-80s flex duct system pulls hot, saturated attic air into the air handler at every gap. The system then spends its effort drying attic air instead of house air.
4. The house itself is leaky: block ranches with original windows and a dryer that vents into the garage. Less common as a primary cause than people assume, but it adds up.
5. Living. Showers without a working bath fan, pots on the stove, a crawlspace under a manufactured home that is wet from May to October and open to the belly-board duct.
6. The shoulder months. In April and October the air conditioner barely runs and the outdoor air is still wet. Nothing is drying the house because nothing is cooling it.

Tonight: the fan setting, the bath fans, the hygrometer

Three things you can do before bed. Set the thermostat fan to AUTO and leave it there. Run the bathroom exhaust fan during every shower and for twenty minutes after, and if the fan is the original 1980s unit that sounds like a lawnmower and moves no air, that is a fix worth making. Note the hygrometer reading at bedtime and again at 7 a.m.; if it climbs overnight while the system idles, that is the shoulder-season pattern and it points toward a dehumidifier. Then put the thermostat back to 76 and see whether the house feels any worse than it did at 71. Usually it does not, and the bill will notice the difference.

Get the humidity measured properly

When the air conditioner needs a partner

Some Lake City houses can be dried by fixing the system: right-sizing at the next replacement, sealing the return duct, setting the fan correctly. Many cannot, because the climate asks more of the air conditioner than cooling can deliver. Fifty-four inches of rain, oppressive humidity for four months, and two shoulder months where cooling barely runs is a load that wants its own machine. A whole-house dehumidifier, ducted beside the air handler and run on its own humidistat, holds the house at 50 percent regardless of what the thermostat is doing and lets you set that thermostat higher. On the visit we measure humidity, temperature split across the coil, static pressure and duct leakage before we recommend one, because selling a dehumidifier to a house whose real problem is a torn return would be the wrong order. When it is the right call, it is the one piece of equipment that changes how a Columbia County house feels more than any other.