Do you need a whole-house dehumidifier in Jacksonville?

Federal guidance points to added dehumidification when indoor humidity stays high. The U.S. Environmental Protection Agency (EPA) sets a target for indoor relative humidity. It says to keep it below 60% if possible, and ideally between 30% and 50%. Department of Energy guidance says an air conditioner alone may fall short of that in hot-humid climates. ENERGY STAR says a whole-home unit "may be the right choice" for humid-climate homes with central air. This guide uses Jacksonville weather data and current federal guidance as of October 2026.

Recommended indoor humidity levels

In its brief guide to mold and moisture, EPA says: "If possible, keep indoor humidity below 60 percent (ideally between 30 and 50 percent) relative humidity." EPA also says "the key to mold control is moisture control."

Moisture in the air alone can sometimes be enough for mold. EPA's mold course says that "humidity or dampness (water vapor) in the air can supply enough moisture for mold growth." It adds that "condensation can be a sign of high humidity." ENERGY STAR's dehumidifier page gives the same range. It says the optimum level for a building "is generally considered to be between 30% and 50%." It adds that "anything above this range may promote mold growth."

Jacksonville's humidity and heat by the numbers

NOAA's 1991–2020 hourly normals come from Jacksonville International Airport. They show how much moisture the summer air carries. On July 15 at 3 p.m., the normal dew point is 72.4°F, with an air temperature of 87.7°F. On January 15 at 3 p.m., the normal dew point is 44.5°F, with an air temperature of 63.3°F. The NOAA normals we used report dew point, not relative humidity. We have not turned them into a humidity percentage.

The airport averages 2,803.2 cooling degree days and 1,227.6 heating degree days a year. It also averages 80.1 days a year at or above 90°F. July has a normal average high of 91.9°F and a normal average low of 73.2°F.

Why an air conditioner may not control humidity on its own

DOE's Building America Solution Center covers this in its whole-house dehumidification guide. Pacific Northwest National Laboratory runs the center. The guide was last updated February 28, 2018. It is more than five years old. It describes ways an air conditioner can leave a home humid, including these two.

The first is oversizing. The guide says an oversized system can short-cycle. A short-cycling system runs for short periods followed by long off periods. It explains, "In homes with over-sized air conditioners, the thermostat quickly reaches the desired set point before moisture can condense on the coil and be removed from the home." It goes on, "In this situation, the temperature in the home drops but the relative humidity climbs."

The second involves milder weather. The guide says conventional systems "generally dehumidify well during peak-load temperatures when the system operates for extended periods." At lower temperatures, it says, the system "cools the house relatively quickly and cycles off, but provides proportionally less dehumidification." The guide adds, "As a result, indoor humidity levels tend to rise."

The guide then says: "In hot-humid climates, the air conditioner alone may not be able to remove enough latent heat to keep relative humidity below 60%." It says the HVAC designer should then consider adding dehumidification controls or a separate dehumidifier. The guide's warm-humid region "includes all of climate zone 1, all of climate zone 2A, and portions of climate zone 3A." A Department of Energy county guide from August 2015 lists Duval County in climate zone 2A. Under that 2015 assignment, Duval County falls in the warm-humid region. We did not check newer code editions.

ENERGY STAR whole-home dehumidifiers

ENERGY STAR says: "If you live in a humid climate and have central air conditioning, an ENERGY STAR certified whole-home dehumidifier may be the right choice for you." It also says: "These systems can be expensive, but they carry significant benefits for relatively well sealed homes with central air systems that see humidity readings above 55% consistently throughout the house."

ENERGY STAR says whole-home units "are typically installed to use your home's air ducts to dehumidify one or more rooms and are often permanent." Its criteria page defines a whole-home dehumidifier by how it uses ducts. The unit uses ducts to bring return air in. It sends dehumidified air out to one or more places in the dehumidified space.

ENERGY STAR whole-home dehumidifier	Minimum integrated energy factor
Case volume of 8.0 cubic feet or less	2.22 liters per kilowatt-hour
Case volume over 8.0 cubic feet	3.81 liters per kilowatt-hour

The current ENERGY STAR specification took effect October 1, 2025. ENERGY STAR says certified dehumidifiers "are 20% more efficient than non-certified models." We found no government source on what a whole-home dehumidifier costs to buy or run in Florida. This guide does not estimate that cost.

When to add dehumidification to an existing home

The Building America guide sets out a test for existing homes. It says, "Add dehumidification to an existing home if indoor relative humidity levels exceed 60% and if moisture issues are apparent, such as mold, mildew, or occupant complaints of humidity, and no water leakage or water intrusion sources are found."

EPA also says to "use air conditioners and/or de-humidifiers when needed." It also says to keep air conditioning drip pans clean and drain lines "unobstructed and flowing properly." If your home stays above 60% after those checks, ask an HVAC contractor about the system's size. You can also ask whether dehumidification controls or a whole-home unit would help.