What Should I Set My AC to When I Leave My Lowcountry Home for the Summer?

Set your thermostat to 78–80°F — and never turn the AC off. That's the short answer for anyone closing up a Lowcountry home for the summer, whether you're a Sun City resident heading north until fall or a Hilton Head Island owner locking up between guests. In a Bluffton or Beaufort County summer, your air conditioner isn't just keeping the house cool. It's the main thing standing between your home and a mold problem, because cooling the air is also how the house sheds humidity.

Why do closed-up homes grow mold so fast?

Mold needs three things: spores (always present in normal air), something to eat (drywall, wood, dust, fabric — your house is a buffet), and moisture. In a Lowcountry summer, outdoor humidity routinely sits high enough that an unconditioned house drifts above 60% indoor relative humidity — and once it stays there, porous materials like drywall, carpet, and wood become hospitable to mold. The EPA recommends keeping indoor humidity below 60%, ideally between 30 and 50%.

A closed-up house makes it worse: no air movement, no one opening doors, closets and cabinets going stagnant, and nobody around to notice a drip under a sink. A small problem in June has all of July and August to become a big one before you walk back in.

The leave-for-the-summer checklist

Set the AC to 78–80°F. You'll often see the Department of Energy's general advice to push the thermostat to 85°F or higher when away — that advice was not written for coastal South Carolina. In our climate, HVAC pros consistently recommend staying in the 78–80°F range so the system keeps cycling and pulling moisture out of the air.

Give the air a path. Leave interior doors, closet doors, and vanity cabinets open so conditioned air reaches the places mold loves — closets, pantries, and bathrooms are where returning owners most often find surprises.

Shut off the water and check the AC drain line. A supply line that fails in week two of a twelve-week absence is how vacant-home horror stories start. Closing the main valve costs nothing. Having your AC condensate drain line checked before you go prevents the irony of the mold-prevention machine causing the leak.

Put eyes (or sensors) on the house. A Wi-Fi thermostat or an inexpensive remote humidity sensor will text you if the system quits in July. A neighbor or house-watch service walking through every week or two is even better — ask them to sniff, not just look. A musty odor is usually the first sign of a problem, well before anything is visible.

What should I do when I come back in the fall?

Trust your nose at the door. The first 30 seconds after months away are the most honest read of your home's air you'll ever get — you've lost your nose-blindness to the house. If you're greeted by a musty smell, if allergies flare within a day or two of being home, or if you find any sign of a leak that ran while you were gone, don't just air the place out and hope.

That's a perfect job for a canine sweep. Cowboy searches every living space and the garage, alerting at the source of mold growth — even inside walls where nothing is visible — by detecting the compounds growing mold releases at concentrations down to parts per trillion. One appointment tells you whether the house spent the summer behaving, or whether something needs attention before the holidays bring family to town.