Every spring, Naples seasonal owners ask the same question on the way out the door: what do I set the air conditioner to? Leave it too warm and the house can turn musty by August. Run it too hard and you pay to cool an empty home all summer. Published guidance offers three main approaches: a thermostat ceiling of about 85°F, a humidistat at 65% or a timer that runs the AC two hours a day. They are not interchangeable.
Naples FL Mold Remediation is a free quote and referral service that connects Naples and Collier County homeowners with Florida-licensed mold assessors and remediators. Below, we compare what UF/IFAS and LCEC actually say, so you can talk it through with your AC company before you leave.
Why humidity, not temperature, is the real target
Mold responds to moisture. LCEC, a Southwest Florida electric cooperative, says in its Vacant Homes guide that "mold and mildew can grow nearly anywhere if the relative humidity is consistently 70 percent or higher." UF/IFAS publication HE887, Closing Your Seasonal Home, explains that "periodic air conditioner operation will remove moisture from your home." In other words, the AC matters here mostly because it dehumidifies.
Naples' outdoor air in the off-season is about as humid as it gets. Our own averages of NOAA hourly observations at Naples Municipal Airport, 2015–2024 (a calculation we made from NOAA data, not an official normal), show mean relative humidity of about 79% to 81% from June through September and a mean dew point near 75–76°F in July and August. The dew point sat at or above 70°F in 99% of July and August hours. Without the AC pulling moisture out, indoor air drifts toward those levels, well above LCEC's 70% mold threshold.
The three approaches compared
| Approach | What the source says | Trade-off |
|---|---|---|
| Timer: AC runs two hours every day | LCEC: "the highest level of security against mildew growth." UF/IFAS Palm Beach County blog: run central AC at least two hours per day. | Predictable moisture removal; uses more power than a humidistat. |
| Humidistat set at 65% | LCEC: cycles the AC "whenever indoor humidity exceeds 65 percent" and "uses the least power." | Only as good as its calibration; UF/IFAS says to have it calibrated by your AC company. |
| Thermostat at 83°F | LCEC: "the least efficient method," recommended "only for short or infrequent trips." | Simple, but the AC may run little on mild days, leaving humidity high. |
| Thermostat no higher than 85°F | UF/IFAS HE887: "Leave your air conditioner set to no higher than 85 degrees (F)." UF/IFAS Palm Beach County blog: 80–85°F. | A ceiling, not a target; pair it with humidity control. |
Notice that the numbers differ: 85°F as a maximum from UF/IFAS HE887, 80–85°F from the UF/IFAS Palm Beach County blog and 83°F from LCEC for short trips only. These are source-attributed ranges, not a single rule, and none of them is ours.
Option 1: The two-hour daily timer
LCEC ranks the timer first for mildew protection. The logic is simple: the system runs a long, steady cycle every day whether or not the thermostat calls for cooling, so moisture comes out of the air on a schedule. The UF/IFAS Palm Beach County Extension blog gives similar advice, suggesting a thermostat setting of 80–85°F with central AC running at least two hours a day. The cost is energy: the system runs on hot, dry days when it might not strictly need to.
Option 2: The 65% humidistat
A humidistat turns the AC on based on humidity rather than temperature. LCEC suggests setting it to cycle the system whenever indoor humidity exceeds 65%, five points under the 70% level it links to mold growth, and says this option "uses the least power." The catch is accuracy. UF/IFAS HE887 says: "Have the humidistat calibrated by your air conditioning company." A sensor that reads a few points low can let the house sit above 70% all summer while showing a comfortable number.
Option 3: Just setting the thermostat
Many owners simply bump the thermostat up and leave. LCEC calls an 83°F setting "the least efficient method" and recommends it "only for short or infrequent trips." UF/IFAS HE887's 85°F figure is a ceiling: do not go higher. On its own, a high setpoint means the AC may run only in the hottest part of the day, which may not remove enough moisture during long, humid stretches.
Is a humidistat necessary in Florida?
No law requires one in a home. Whether you need one depends on how long you are away and how you plan to run the AC. LCEC presents the humidistat as one of three options, the most energy-efficient one, not as mandatory. If you choose a timer instead, LCEC rates that the most protective. If you rely on a thermostat alone for a full summer, you are using the method LCEC calls least efficient and recommends only for short trips. If you do use a humidistat, get it calibrated.
What indoor humidity should a Florida house have while you're away?
The sources we rely on give two useful markers rather than one ideal number: LCEC's 70% level, above which "mold and mildew can grow nearly anywhere" if it stays there consistently, and its 65% humidistat trigger. A small battery hygrometer near the thermostat lets a house-checker read the actual humidity on each visit.
Don't forget the AC system itself
All three approaches assume the system works. A clogged condensate drain line, a dirty filter or a failing component can leave an empty house warm and wet for weeks. Book a service visit before you leave, and ask the technician to check the drain line and pan and calibrate any humidistat, as UF/IFAS advises. UF/IFAS HE887 also notes that "a dehumidifier operated by a drain to carry away moisture can help, though not as much as air conditioning."
If mold is already growing inside the air handler or ducts, that is a different job. Typical national ranges from cost guides, 2025–2026, put HVAC system and duct mold remediation at about $3,000–$10,000 (estimates, not quotes; the real price comes from a licensed pro's on-site assessment). Florida's definition of mold remediation in s. 468.8411(5) also says the work "may not be work that requires a license under chapter 489 unless performed by a person who is licensed under that chapter," so ask how HVAC repairs will be handled. This is general information, not legal advice. Our AC and HVAC mold page covers the signs to look for.
Putting it together
- Pick a strategy: two-hour daily timer (most protective per LCEC) or 65% humidistat (least power per LCEC)
- Keep the thermostat no higher than 85°F (UF/IFAS HE887)
- Have the humidistat calibrated and the condensate drain cleared before you leave
- Add a drained dehumidifier as a backup, not a substitute
- Leave a hygrometer and ask whoever checks the house to note the reading
For the full departure routine, see our Naples closing-up checklist and the seasonal and second-home mold page.
Came back to a musty house anyway? EPA's mold guide says homeowners can usually handle a moldy area "less than about 10 square feet," and Florida's licensing definitions in s. 468.8411 cover mold growth greater than 10 square feet. Ask any company for its Florida license number and verify it at MyFloridaLicense.com. If anyone has health concerns, talk to a doctor. Tell us what you're seeing and we'll help you get quotes from licensed local pros, or check typical prices in our mold remediation cost guide.
Frequently asked questions
What should I set my AC to when I leave my Florida home for the summer?
UF/IFAS publication HE887 says to keep the air conditioner set no higher than 85 degrees F. LCEC's Vacant Homes guide ranks a timer that runs the AC two hours every day as the most protective against mildew, a humidistat set at 65% as the option that uses the least power, and an 83 degree thermostat setting as least efficient, for short trips only.
Is a humidistat necessary in Florida?
It is not required, but it is one of the options LCEC recommends for vacant Southwest Florida homes. LCEC says a humidistat set to cycle the AC whenever indoor humidity exceeds 65 percent uses the least power. UF/IFAS advises having the humidistat calibrated by your air conditioning company, because an inaccurate sensor can let humidity stay high without you knowing.
What humidity level causes mold in a Florida house?
LCEC's Vacant Homes guide says mold and mildew can grow nearly anywhere if the relative humidity is consistently 70 percent or higher. That is why LCEC suggests a humidistat setting of 65 percent. Our own averages of NOAA hourly data show Naples outdoor humidity around 79 to 81 percent from June through September, so a closed house needs active moisture removal.