Where Your Thermostat Sits Changes How Your AC Runs

Reviewed by Tom Dickerson · 365 Solutions HVAC & Plumbing · Florida Certified Mechanical Contractor CMC1251581

The thermostat only knows the temperature of the wall it is mounted on. If that wall is not representative of the house, the system runs to the wrong target all day.

Bad locations we see constantly

On a wall that gets afternoon sun through a sliding door: the system overcools the rest of the house every afternoon. Directly across from a supply vent: the thermostat is satisfied minutes after the system starts, so it short-cycles and never pulls humidity out. In a dead-end hallway with the doors closed: the hallway is comfortable, the bedrooms are not. Next to the kitchen: every dinner turns the AC on. On an exterior wall: it reads the wall temperature, not the room.

Where it belongs

An interior wall, about five feet up, in a room the family actually uses, away from vents, windows, lamps and the TV. In most St. Johns County single-story plans that is the main living area; in two-story Nocatee and Durbin Crossing plans the ground-floor thermostat cannot see the upstairs at all, which is why the bonus room is always hot.

When moving it is not enough

If the house has hot and cold rooms no matter where the thermostat is, the fix is a remote sensor (most smart thermostats support them and average the readings) or a zoning system with dampers and a second thermostat. For a bonus room or garage that is never right, a mini-split is often simpler than zoning.

A note on smart thermostats

Nest, ecobee and Honeywell all need a common (C) wire. Many 2015–2022 builder homes here were wired without one, which is why the thermostat drops off Wi-Fi or the system behaves strangely after a DIY install. We can add the wire or a power adapter and set it up correctly.