45–55% — Higher than a cold climate — chasing 40% here costs a fortune
This is the climate where almost every piece of general humidity advice needs inverting. For five or six months a year the outdoor air holds more water than your indoor air, so opening windows adds moisture, and every leak in the building envelope is a moisture source rather than a drying opportunity.
It is also the climate where the air conditioner is doing double duty — cooling and dehumidifying — and where it most often fails at the second job.
Why the AC leaves the house clammy
An air conditioner removes moisture as a side effect of cooling: warm humid air passes over a cold coil, water condenses on it and drains away. That only happens while the unit is actually running. An oversized system cools the house to the setpoint quickly and shuts off — short cycles, little run time, and very little moisture removed. The house hits 74 °F and 65% humidity and feels worse than it did.
This is why so many homes in hot-humid climates end up needing a dehumidifier despite having plenty of cooling capacity. The fix is run time, not tonnage: a variable-speed or two-stage system, a lower fan speed, or a standalone or whole-house dehumidifier that handles the latent load directly.
The second regional issue is below the floor. Vented crawl spaces are common here and they are precisely wrong for the climate — warm humid outdoor air entering a cool crawl space condenses on the framing all summer. Sealing and encapsulating is standard practice now for good reason.
What is your reading telling you?
- Dew point
- 53 °F
- Mold risk, cold walls
- Moderate
Still inside the accepted range, but this is where cold surfaces begin to sweat.
What to do here
Ranked by what it costs you, and ordered for this climate rather than in general.
Keep windows shut from spring through fall. Check the window calculator rather than guessing.
Run the AC on a normal cooling cycle, not fan-only. Fan-only re-evaporates water off the coil back into the house.
Keep bathroom and kitchen extraction running — source removal matters in every climate.
Check the AC condensate drain is clear. A blocked drain returns the water the system just removed.
Put a hygrometer downstairs and in any below-grade or crawl space area, and read them in July.
Add a dehumidifier targeting 50% if the house sits above 55% with the AC running.
Specify an ERV rather than an HRV if you are adding mechanical ventilation — it limits how much moisture comes in with the fresh air.
Seal and encapsulate the crawl space. In this climate, venting it is the problem rather than the solution.
What will not work here
-
Opening windows to "air it out"
For most of the year outdoor air is wetter than indoor air. This is the single most common mistake in the region.
-
A bigger air conditioner
More capacity means shorter cycles and less moisture removed. Run time is what dehumidifies, not tonnage.
-
Ventilating the crawl space
Warm humid air on cool framing condenses. Seal it instead.
-
Targeting 40% indoors
Achievable but expensive, and unnecessary. 45–55% suppresses mold and dust mites without the energy bill.
Through the year
Spring
The changeover. Warm days with the AC not yet running let humidity climb indoors. This is when musty smells first appear.
Summer
Peak. Windows shut, AC running proper cycles, dehumidifier for anything below grade. Never ventilate to "air the house out".
Fall
Hurricane and storm season moisture, plus the AC running less. Watch for damp returning as run time drops.
Winter
The only period when ventilation helps. Mild, drier air — a good time to air the house properly.
Common questions
What humidity should I keep my house at in Florida?
45–55%. Below 60% suppresses mold and dust mites, and chasing 40% in a hot-humid climate costs a great deal of energy for no additional benefit.
Does a bigger air conditioner dehumidify better?
No — the opposite. Moisture is removed while the coil runs, so an oversized unit that satisfies the thermostat in short bursts removes less water than a smaller one running longer. Run time dehumidifies, not tonnage.
Should I ever open windows in a hot-humid climate?
In winter and on cool dry days, yes. From spring to fall the outdoor air generally carries more moisture than your conditioned indoor air, so ventilating raises indoor humidity.
Sources
- US EPA — Mold and moisture guidance — the 30–50% range and the 10 sq ft remediation threshold
- ASHRAE Standard 55 — Thermal environmental conditions for human occupancy — indoor comfort and humidity limits
- US DOE 10 CFR 430 — Dehumidifier test procedure — the 2019 move to 65 °F rating conditions