Sticky at 74 in a 1910 frame house and sticky at 74 in a 2020 build: Palatka's two humidity problems
By the thermostat, the house is cool. By the bedsheets, it is not. In Putnam County, the year the house went up explains most of the gap.
Two houses, one afternoon
A family in a 1910 frame house in the North Historic District keeps the thermostat at 74 and the house feels like a bathroom after a shower. Across town on a cleared lot built in 2020, a couple keeps theirs at 74 too, and their house feels the same way. They would compare notes and conclude Palatka is just humid, which it is. But the two houses are damp for opposite reasons, and the equipment that fixes one does nothing for the other.
The climate factor
The St. Johns River basin is one of the more humid places in an already humid state. Inland from the coastal breeze, dew points sit in the mid-70s from June into September, and the county picks up close to 53 inches of rain a year, much of it in afternoon storms that leave the ground and the air saturated. Open water is everywhere: the river, Dunns Creek, Crescent Lake, the Interlachen lakes. The shoulder months, May and October, are the sneaky ones: warm enough to be humid, not hot enough to make an air conditioner run long.
An air conditioner removes moisture only while it runs. In a climate like this, anything that shortens its run time, or lets moisture in faster than it can take it out, leaves the house wet.
What the old house is doing
The 1910 frame house is porous. Moisture comes up from the crawlspace through the floor, in through the sash windows and the clapboard walls, and down from an attic that was never sealed. The ducts, if it has them, were retrofitted through closets in the 1980s and leak at every joint, some of them under the floor where they pull in crawlspace air directly. The house takes on water faster than its air conditioner can remove it, and the air conditioner is probably oversized because someone once tried to beat the heat with tonnage.
What that house needs: the crawlspace addressed with a vapor barrier and sealed or replaced ducts, then a whole-house dehumidifier sized for a leaky building, then, when the system is replaced, a correctly sized variable-capacity unit that runs long and slow.
What the new house is doing
The 2020 house is the opposite. It is tight. Little outdoor moisture gets in. The moisture that makes it damp is generated inside: four people breathing, showers, cooking, the dryer. The house holds it, because it is built to hold conditioned air. The builder-grade single-stage air conditioner is oversized for a well-insulated house, so it cools in a few minutes and quits, and in May and October it hardly runs at all. The humidity has no exit.
What that house needs: a whole-house dehumidifier that runs on a humidistat regardless of the thermostat, controlled ventilation through an energy-recovery ventilator so the inside air is exchanged without importing the outdoor dew point, and when the system is replaced, a smaller two-stage or variable unit.
How we approach it
We bring a hygrometer and we measure: indoor humidity in three rooms, the temperature of the air leaving the coil, the run time of a cycle, and the static pressure in the ducts. In a crawlspace house we look under the floor. In a tight house we ask about the exhaust fans and the ventilation. The recommendation follows the numbers, and sometimes the first recommendation is not equipment at all: switching the fan from On to Auto, sealing a return, or putting plastic down in a crawlspace.
The maintenance that keeps it dry
A clean coil condenses more water than a dirty one. A clear drain lets it leave; a scaled one, which Putnam’s iron-and-sulfur well water produces, backs it up. A correctly charged system runs its coil at the right temperature. Two visits a year from the Palm Coast shop, one before the season in spring and one after it, cover all three. A whole-house dehumidifier wants its filter cleaned and its drain flushed on the same schedule.
Damp-house questions from both ends of Palatka's housing stock
Our crawlspace in Palatka Heights smells like earth and the floors feel cool and damp. Is that an HVAC problem?
It is a moisture problem that the HVAC system is being asked to solve alone. Ground moisture rises through the floor of a crawlspace house all summer. A vapor barrier on the ground and sealed ducts under the floor are the first fixes; a whole-house dehumidifier is what finishes the job.
Why is our new house damp in October when the air conditioner barely runs?
Because it barely runs. A tight new house holds moisture from cooking, showers and breathing, and on a 78-degree October day the air conditioner cycles briefly and removes very little of it. The house needs dehumidification that works independently of temperature.
Will a bigger air conditioner dry the house better?
The opposite. A larger unit chills the air and quits sooner, giving the coil little time to condense anything. The damp-and-cold house is very often an oversized system.
What setting should the thermostat be on: Auto or On?
Auto. Left on On, the blower carries the coil’s standing water back into the rooms during every rest period, raising humidity. In a damp Palatka house, that one switch can be worth several percentage points.
Sheets damp with the thermostat satisfied?
Call. We measure before we recommend, and the fix depends on your house.