The Best Thermostat Settings for a South Carolina Summer

Ask an energy advisor and you'll hear 78°F for summer. Ask a Grand Strand homeowner in August and you'll hear laughter. The truth: the "best" setting is a tradeoff between comfort, humidity control, and your electric bill — and humidity is the part most advice skips.

The number everyone quotes: 78°F

The U.S. Department of Energy has long suggested 78°F as the summer setting when you're home and awake — each degree lower measurably increases runtime and cost. It's a reasonable starting point, not a law. Many people find 76–78°F comfortable if humidity is under control, because dry 78° air feels cooler than humid 75° air. Which brings us to the real issue.

Humidity is the actual thermostat

In coastal South Carolina, comfort is mostly a humidity story. At 70% indoor humidity, 76°F feels sticky and gross; at 45%, the same 76°F feels fine. Your AC dehumidifies as it cools — but only while running. Strategies that help:

• Don't overshoot the setpoint. Dropping to 68°F "to cool faster" doesn't cool faster — ACs run at one speed (unless variable-speed) — it just runs longer and can overcool without extra dehumidifying benefit.
• Use AUTO, not ON, for the fan. "ON" keeps blowing between cooling cycles, re-evaporating moisture off the coil back into your house. AUTO lets the coil drain properly.
• Consider a whole-home dehumidifier if indoor humidity stays above 55–60% despite the AC running normally. It's often cheaper than overcooling to chase comfort.

When you're away: the setback rules

Gone for the workday? Setting up 7–10 degrees (say, 78° to 85°) saves meaningful energy. But in our climate, two cautions:

• Don't go above the mid-80s. Sustained indoor temps in the high 80s with our humidity invite mold growth and can damage wood floors, cabinets, and electronics. For vacations, 80–82°F with the fan on AUTO is the safe zone.
• Recovery takes time. Coming home to 85° and expecting 74° in twenty minutes leads to disappointment. Smart thermostats can start recovery before you arrive — or just accept a gradual cooldown.

Night settings and ceiling fans

Most people sleep better a few degrees cooler. Try 74–76°F at night with a ceiling fan running counterclockwise — the breeze makes it feel 3–4 degrees cooler, letting you keep the thermostat higher. Fans cool people, not rooms: turn them off when you leave.

Heat pump owners: one special rule

If you heat with a heat pump in winter, avoid big manual setbacks — cranking it up several degrees triggers expensive auxiliary heat strips. In summer, though, setbacks work the same as any AC. (This post is about summer; winter is a different game.)

When settings can't fix it

If 72°F on the thermostat gives you 78°F in the living room, the setting isn't the problem. Suspects: low refrigerant, a frozen coil, leaky ducts dumping cool air into the attic, or an aging system losing capacity. No thermostat setting overcomes equipment problems — that's a service call.

Placement matters as much as the setting

You can set the perfect temperature and still be uncomfortable if the thermostat is lying about the house. Common placement sins we see in Grand Strand homes:

• Direct sunlight. A thermostat on a sun-blasted wall reads 80° when the house is 74° — and runs the AC endlessly trying to satisfy a phantom temperature.
• Near heat sources. Above a TV, beside a lamp, near the kitchen — all fool the sensor upward.
• In a draft or dead hallway. A thermostat in a rarely-used hallway with no airflow doesn't represent any lived-in room.
• Too close to a supply vent. Cold air blowing directly on it satisfies the thermostat while the rest of the room swelters.

The fix is relocation to an interior wall in a frequently used room, away from vents, sun, and appliances — roughly chest height. Some smart thermostats offer remote room sensors that average temperatures across rooms, which solves placement problems without moving wires. Either way, a thermostat reading the wrong temperature makes every "best setting" advice meaningless.