In a Florida summer, a house can feel cool and still be too damp. Too much moisture in the air is what lets mold grow, and an A/C that isn't draining or running right is often part of the reason. The good news is that measuring it is cheap and easy. This guide shows how to check your home's humidity with a hygrometer, what number to aim for, and the simple A/C checks that go with it, following the EPA, ENERGY STAR, the Florida Department of Health and the University of Florida's IFAS extension.
Stop and call a pro before you start if:
- Water is near outlets, a light fixture or the electrical panel, or the ceiling is sagging. Our advice: stay out of that area, turn off power at the breaker if you can do it safely from a dry spot, and call a licensed electrical contractor.
- You'd have to open the air handler, its panels or its wiring to reach something. Florida's contractor law lists installing condensate drains and A/C control wiring in the scope of licensed A/C and mechanical contractors (s. 489.105(3)). This guide only covers what you can see without opening the unit, plus the filter.
- You see mold in the A/C system or ducts. The EPA says "Do not run the HVAC system if you know or suspect that it is contaminated with mold."
- Mold covers more than about 10 square feet (the EPA says to consult its mold remediation guide, and to use an experienced contractor if you hire one), or the water came from sewage or a flood (the EPA says to call in a professional for sewage or other contaminated water). See our guides to small mold patches and floodwater cleanup.
- You'd be disturbing old insulation, pipe wrap or textured ceilings near the unit. The EPA lists vermiculite attic insulation, textured paint and patching compounds on walls and ceilings, and hot water and steam pipes coated or wrapped with asbestos material among places asbestos may be found, and says "Taking samples yourself is not recommended."
- The home was built before 1978 and you'd be scraping or sanding paint. The EPA says it may have lead-based paint and recommends testing or a lead-safe certified contractor.
What you'll need
| Item | Why | Where to buy |
|---|---|---|
| Hygrometer (humidity gauge) | The EPA says relative humidity can be measured with "a small, inexpensive ($10-$50) instrument available at many hardware stores" | Home Depot · Lowe's |
| Replacement A/C filter in your system's size | ENERGY STAR says to inspect, clean or change the filter monthly | Home Depot · Lowe's |
| Flashlight | To look around the air handler and the drain pan you can see | Home Depot · Lowe's |
| Old towels | The EPA says to dry condensation and wet surfaces quickly | Your linen closet |
Step by step
Step 1: Get a hygrometer
A hygrometer is a small gauge that reads relative humidity, usually with the temperature. The EPA says you'll find one for $10 to $50 at many hardware stores. ENERGY STAR also suggests one if your dehumidifier doesn't show the humidity level: hang it near the dehumidifier.
Step 2: Read it and compare
The agencies don't give the same number, so here's what each says:
| Source | Recommended indoor humidity |
|---|---|
| Florida Department of Health | Below 60%; "below 50% is best for controlling both mold growth and dust mites" |
| U.S. EPA | Below 60%, ideally 30–50% |
| ENERGY STAR | 30–50%; "Anything above this range may promote mold growth" |
| UF/IFAS (FY1044) | Below 70%, ideally 45–60% |
If your reading is above 60%, keep going with the steps below. The UF/IFAS publication says that during rainy, humid weather "the air conditioner often does not operate long enough to adequately control the indoor relative humidity," so check on a few different days.
Step 3: Look for condensation
The EPA says that if you see "condensation or moisture collecting on windows, walls or pipes," act quickly to dry the wet surface and reduce the moisture source, and that condensation "can be a sign of high humidity." Wipe it dry with a towel and note where it shows up.
Step 4: Check the A/C filter
ENERGY STAR says to "inspect, clean, or change air filters once a month" in your central air conditioner, furnace or heat pump, and that "your contractor can show you how to do this." The EPA says to follow the instructions on the filter's package. A UF/IFAS moisture fact sheet says to make sure "the filter is not clogged."
Step 5: Look for standing water around the air handler
The Florida Department of Health says to "check around air handling units (air conditioners, furnaces) for standing water." The EPA says that in the drain pan, "substantial standing water and/or debris indicates a problem requiring immediate attention," and to check any insulation near the cooling coils for wet spots. Look only at what you can see with a flashlight. Don't open panels.
If you find standing water, call a licensed A/C contractor. ENERGY STAR says "a plugged drain can cause water damage in the house and affect indoor humidity levels." We found no official guidance on homeowners flushing drain lines, so follow your equipment maker's manual or leave it to the contractor.
Step 6: Use the A/C or a dehumidifier, and know when that's not enough
The EPA says to "use air conditioners and/or de-humidifiers when needed." The Florida Department of Health adds a warning: if your home has central air and you need a dehumidifier to get below 60%, "you should have the air conditioning system examined for problems."
Step 7: Keep checking
The EPA says to keep air conditioning drip pans clean and drain lines "unobstructed and flowing properly," and that yearly maintenance of a heating and cooling system "consists of regular cleaning of drain pans and heating and cooling coils, regular filter changes and yearly inspections of heating equipment." ENERGY STAR lists checking the condensate drain as part of a contractor's check-up. Ask your A/C contractor to clean the coils and drain pans when they service the system, as the EPA suggests.
How long it takes
None of our sources give times for these checks. ENERGY STAR's monthly filter check is the only schedule they set for homeowners.
Stop and call a pro if, once you start, you find:
- Substantial standing water or debris in the drain pan, or water on the floor around the air handler. The EPA says that needs immediate attention.
- Humidity that stays above 60% even with the A/C running. The Florida Department of Health says to have the system examined.
- Wet insulation near the cooling coil (EPA), or a stain in the ceiling under an attic unit.
- Mold larger than about 10 square feet, or mold in the A/C or ducts (EPA).
When water has already reached the ceiling or walls, that's where we come in: see our drywall, ceiling and interior repairs, and read our Palm Harbor post on A/C condensate leaks and humidity.
Frequently asked questions
What humidity should my house be in Florida?
The Florida Department of Health says below 60%, and below 50% is best for controlling mold and dust mites. The EPA says ideally 30 to 50%; a UF/IFAS publication suggests 45 to 60%.
How much does a hygrometer cost?
The EPA says a humidity meter is "a small, inexpensive ($10-$50) instrument available at many hardware stores."
How often should I change my A/C filter?
ENERGY STAR says to inspect, clean or change the filter once a month, and the EPA says to follow the instructions on the package.
Why is my house humid when the A/C is on?
The UF/IFAS extension says that during humid, rainy weather the A/C often doesn't run long enough to control humidity. The Florida Department of Health says that if you need a dehumidifier to get a centrally air-conditioned home below 60%, have the system examined for problems.
Sources
- U.S. EPA: A brief guide to mold, moisture and your home
- U.S. EPA: Mold cleanup in your home
- U.S. EPA: Should you have the air ducts in your home cleaned?
- U.S. EPA: Care for your air, a guide to indoor air quality
- ENERGY STAR: Maintenance checklist
- ENERGY STAR: Dehumidifiers
- Florida Department of Health: Mold
- UF/IFAS: Energy efficient homes, indoor air quality and energy (FY1044)
- UF/IFAS: Moisture control in your home, part 1 (FCS3256, archival)
- Florida Statutes s. 489.105 (2026)
- U.S. EPA: Learn about asbestos
- U.S. EPA: Protect your family from exposures to asbestos
- U.S. EPA: Lead-safe renovations for DIYers