As of late September 2026, the afternoon sun here in Florida still comes through the sliders like it’s July, and in Port St. Lucie the easy habit is to leave the blinds on that side wide open all day. The AC is running, so why fuss? A little sunlight through the glass can’t matter much with the compressor doing the work. I ran my own house that way for years after coming down from Jersey, where a sunny window in October was something you wanted.
FPL, which sends the power bill to my house here in Port St. Lucie, answers this one on its energy-expert page. Asked whether the A/C costs more to run during the day, it says: “In summer, yes—it is hotter during the day so your A/C will have to work harder to keep your home cool.” Its advice to save is to keep the blinds closed and use a programmable thermostat to reduce the strain on your system.
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What the Department of Energy says
Its Energy Saver guidance on window coverings describes my old habit almost exactly: 75% of residential window coverings stay in the same position every day, according to a Department of Energy study. I hung mine once and then treated them as furniture.
Why the glass matters even with the AC on
The same Energy Saver page gives the mechanism: in cooling seasons, about 76% of the sunlight that falls on standard double-pane windows enters to become heat. That heat lands inside the room the AC is trying to cool, which is the extra work FPL is describing on a summer afternoon…