As of late September 2026, every mild, breezy day in Port St. Lucie tempts somebody on my street to switch off the air conditioner and open every slider in the house to air it out. It feels like giving the compressor a break after a long summer, and outside air feels cleaner just because it is moving. I did the same for a couple of years after coming down from New Jersey, where I never once thought about what rides in on a breeze. Northern house logic does not work here.
FPL, the utility that sends my electric bill, says it plainly in its heating and cooling guide: close exterior windows and doors tightly when your heater or A/C is running. Its air conditioning tips add that high humidity can cause mold and mildew. Here in Florida, that is the whole problem with a pretty afternoon.
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What UF/IFAS says
A UF/IFAS county extension office puts numbers on the gap. The average relative humidity in Florida is 74.5%, it says, while a perfect indoor humidity is around 50%. And about leaving the house open into the evening: “At night, Florida can get 80 to 100 % humidity levels. And if your windows are open, you are letting all that humidity into the house.”
Why the AC ends up working harder
Your air conditioner is how the house gets dried out. As warm, humid air passes over the evaporator coils, UF/IFAS explains, moisture condenses and drains away before cooler, drier air goes back into the rooms. Researchers at the Florida Solar Energy Center compare the air conditioner to the only bilge pump a building may have…