Humidity and Your AC in Panama City: Why the House Feels Clammy

What an air conditioner does with moisture

Air conditioning does two jobs at once. Cooling the air is the sensible load; condensing water vapor out of it is the latent load. Both happen on the same cold indoor coil: as warm, humid air passes over it, the air cools and, because cold air holds less moisture, water condenses on the fins and drains away. That is why a working system in July produces a steady stream of condensate all day, and why a blocked drain line is a summer emergency.

The catch is that dehumidification is slow. The coil has to get cold and stay cold, and air has to keep moving across it, for moisture to come out in quantity. A system that runs in long, steady cycles dries the house. A system that runs in short bursts cools it and stops, and the Building America program describes what happens next: the unit "will not run for a significant enough time to allow the condensate to drain off of the evaporator coil," and the water that did condense "will evaporate back into the airstream as the fan continues." The house gets cooler and wetter at the same time.

Why Panama City is the hard case

Three numbers explain it. First, the latent share. The Florida Building Commission's energy and humidity forum put moisture removal at about 20% of a Florida home's seasonal cooling energy, against roughly zero for the same house in Phoenix. Second, the design humidity. NOAA's engineering weather data for Tyndall AFB gives Panama City a 1% cooling design condition of 90°F dry bulb with a 79°F coincident wet bulb; a wet bulb that close to the dry bulb means the air is carrying a great deal of moisture even on the hottest afternoon. Third, the daily cycle. The Florida State Climatologist describes a typical summer day as relative humidity rising "to over 90%" overnight and falling "to 60% or less" by afternoon, with dew points in the high 60s to low 70s every day, and notes that "coastal areas are a little more humid than inland." Panama City has no official humidity normal of its own; the nearest station with one, Apalachicola, averages 86 to 88% on July and August mornings and 71 to 75% in the afternoons.

Put those together and the shape of the problem appears. The air conditioner is sized for the 90°F afternoon, when the sensible load is high and the system runs hard. But most summer hours are not that afternoon. They are the 76°F morning at 90% humidity, when the house needs very little cooling and a great deal of drying, and a system sized for the afternoon barely runs.

Part load: where the clammy hours come from

Engineers call the mild hours part load, and the research is clear that this is where humidity control fails. NREL modeling of a code-built home in Houston, a comparable hot-humid climate, found that at the 1% dew-point design condition the air conditioner needs to run only about 35% of the time, and that in humid climates the air conditioner on its own meets only about 50 to 65% of the moisture load at part load. Building Science Corporation has reported the same pattern: high indoor humidity typically occurs at part load, not at peak. The Florida Building Commission's forum summarized it in one line: "Oversizing results in shorter run times, less water vapor condensed out of the air, and higher indoor humidity."

This is why a correctly sized system matters more here than the energy figures alone suggest. In the FSEC study of 368 new Florida homes, units at 1.0 to 1.2 times their Manual J load used about 3.7% more cooling energy than right-sized ones, and units at 1.2 to 1.5 times used about 9.3% more. Modest. The comfort penalty is the strong case: a right-sized unit runs longer at part load, and every extra minute of run time is moisture leaving the house. ACCA's guidance puts it plainly: avoiding oversizing "can be even more critical in humid climates."

Which humidity problem do you have?

Five patterns account for most complaints. The symptoms overlap, so use the table as a starting point and have a technician confirm with measurements.

The oversizing trap, and why turning the thermostat down backfires

The instinct when a house feels sticky is to drop the setpoint from 74 to 71. On an oversized system that lengthens each cycle slightly but does not change the pattern: the unit still hits the new number quickly and stops. Meanwhile the house is colder, so the same moisture reads as a higher relative humidity. The DOE's Better Buildings program describes the loop: "Oversizing to solve a comfort complaint usually leads to more comfort complaints." The fix is run time, not a lower number.

How common is oversizing? In the 1996 FSEC survey, 38.5% of Florida contractors admitted doing it on purpose, most often because the customer asked. In the 368-home study the following year, more than half the new homes had capacity above 120% of their Manual J load. If your system was sized by copying the old one, or by square footage, the odds are not in your favor. Florida's energy code now caps new-system capacity at 115% of the calculated load and prohibits safety factors, which is the state's own verdict on the practice.

Sensible heat ratio: the number on the spec sheet that matters here

Every air conditioner splits its capacity between cooling and drying. The sensible heat ratio (SHR) is the share that goes to temperature: a unit with an SHR of 0.75 at design conditions puts a quarter of its capacity into moisture removal. Two "3 ton" units can have different ratios, and the difference shows up in your house, not on the label. UF/IFAS puts the warning directly: "Many high SEER units have poorer humidity removal capacity, so verify the SHR before purchasing." ENERGY STAR's HVAC design supplement calls for enough latent capacity in warm-humid climates to hold indoor humidity at 60% or below.

Practically: when you compare quotes, ask for each unit's sensible and latent capacity at Panama City's design conditions from the manufacturer's expanded performance data, and compare the latent figure to the latent load in the Manual J. A unit that meets the total load but falls short on latent will cool the house and leave it damp. Variable-speed equipment earns its place here because it can run at low capacity for hours, which is exactly the long, slow run that pulls moisture out.

Airflow and the blower setting

The same unit can dry the house or fail to, depending on how fast the blower pushes air across the coil. More airflow means more sensible cooling and less moisture removal; less airflow means a colder coil and more condensation; too little, and the coil can freeze. Building America advises considering fan speed before upsizing equipment, and a dehumidification setting is only useful if it was actually configured at installation. Before you replace anything, ask whether the blower is set for a humid climate.

Ducts: the leak you cannot see

A return duct in a Bay County attic is sitting in air that reaches about 120°F on a summer afternoon and is at least as humid as outside. Any leak on the return side pulls that air straight to the coil. FSEC modeling found a 15% return leak from the attic can cut a system's effective capacity and efficiency by half, and in a 24-home Florida field study, duct repair alone cut cooling energy use by 18%. If the house is humid and the ducts have never been tested, test the ducts first; it is often cheaper than any equipment change and sometimes it is the whole answer.

When a dehumidifier beats a bigger air conditioner

A whole-house dehumidifier is a ducted unit that removes moisture without needing a cooling call, so it keeps working through the mild, muggy hours when the air conditioner barely runs. It is the right answer when the system is correctly sized, the ducts are tight, the blower is set properly, and the house is still above 60% in the shoulder months. DOE Building America guidance puts the threshold for considering separate dehumidification at a summer dew point above about 55°F; Panama City's summer dew points sit in the high 60s to low 70s. A dehumidifier adds some heat to the house and uses electricity, so it is a complement to a right-sized system, not a substitute for sizing it properly.

What it is not: a fix for an oversized air conditioner. Adding a dehumidifier to a short-cycling system treats the symptom while the unit goes on wearing itself out with starts and stops. If the system is less than ten years old and badly oversized, the honest options are a blower and control adjustment now and a correctly sized unit at replacement.

Vacation rentals and empty houses

A home that sits empty for stretches has a humidity problem of its own, and the published evidence is thin but useful. In an FSEC study of three unoccupied Florida homes, indoor humidity ran between 62 and 73% with the air conditioning off, and setting the thermostat to 85°F did not control it. What did work was a short daily cooling period, running the system at 74°F for two hours in the early morning, or a dehumidifier on a timer, either of which held humidity under 65%. Lee County's electric cooperative advises setting a vacant home's thermostat to 80°F and warns that mold becomes likely at a sustained 70%. For a rental, the practical rule is that the system needs run time even when nobody is there, and the cheapest way to get it is a thermostat schedule or a dehumidifier rather than a lower setpoint all week.

What good looks like

A hygrometer costs little and tells you more than the thermostat does. Indoor relative humidity below 60% through a Panama City summer, and ideally in the 30 to 50% band the EPA recommends, with no condensation on supply registers or cold water lines, is a system doing both halves of its job. If the number sits above 60% for days at a time, work through the table above in order: sizing and cycling, blower setting, ducts, then dehumidification. Each step is cheaper than the next, and the expensive one is rarely the first that is needed.

Sources

Researched against the sources below and last reviewed October 17, 2026. Figures are quoted with their dates; where the evidence is dated or thin, the text says so.

• Florida Building Commission, Energy efficiency and moisture control in the Florida climate: energy and humidity forum report (2007)
• Building America, Why right-size? and Designing forced-air HVAC systems (2010); Building America Solution Center, Mechanical air conditioning; DOE Better Buildings, Right-sizing HVAC (2023)
• National Renewable Energy Laboratory, Humidity control in hot-humid climates (Winkler and Booten, 2016)
• Building Science Corporation, Rudd (2007) on part-load humidity, and Effects of air conditioner sizing on energy consumption (Townsend and Ueno, 2008), which found no significant energy difference from resizing in a hot-dry climate
• ENERGY STAR, National HVAC Design Supplement to Standard 310, Rev. 14 (2025)
• Florida Solar Energy Center, How contractors really size air conditioning systems (1996); Are energy savings due to oversizing of air conditioners real? (1997); Measured impacts of proper air conditioner sizing in four Florida case study homes (2006); Duct leakage research (Cummings et al., 1990)
• University of Florida IFAS Extension, Energy efficient homes: air conditioning (rev. 2025)
• Air Conditioning Contractors of America, Come on, you can just add a ton, can't you?
• US EPA, A brief guide to mold, moisture and your home
• NOAA National Centers for Environmental Information, Engineering weather data: Tyndall AFB (1988 to 2017); Florida Climate Center, Humidity in Florida and Relative humidity normals
• Lee County Electric Cooperative, guidance on thermostat settings for vacant homes (not available as a stable link); FSEC study of three unoccupied Brevard County homes (2005), as summarized in FSEC's published research