As of late September 2026, my AC in Houston is still running like it’s July. When I bought this house, one of the first things I did was put in a smart thermostat. I connected the app, picked 72, and left it there all day, every day. I thought the smart part was the savings. Turned out the smart part only matters if you use it.
The Public Utility Commission of Texas doesn’t talk about hardware at all in its own energy tips. It talks about a schedule: set your AC 5˚ higher when you’re gone more than 4 hours, and between 3 and 7 p.m. aim to keep it at 78° or higher. That’s the whole trick, and a thermostat parked at one number does none of it.
What ENERGY STAR says
ENERGY STAR certifies smart thermostats using a year of data from real customers’ homes, and to pass, a model has to cut cooling run time by at least 10% and heating run time by at least 8%. But look at what it counts. Its savings metrics “only reflect savings from setback and set-up.” The baseline is the runtime needed to hold the house at a constant 72 degrees F.
Read that again with my first summer in mind. A smart thermostat held at 72 around the clock isn’t beating the baseline. It is the baseline.
Why the box on the wall isn’t the savings
The saving comes from the hours the house spends at a less demanding temperature. The Energy Department explains it for winter: “the longer you keep your thermostat at the lower temperature, the more money you save because your home has lost less energy than it would have at a higher indoor temperature.” Summer is the same idea in reverse. A warmer setting while you’re out means the AC has less work to do…