A smart thermostat is a Wi-Fi-connected thermostat that controls a heating and cooling system through schedules, occupancy sensing, geofencing and a smartphone app. Many models learn household routines and report runtime and maintenance alerts, and ENERGY STAR recognizes models meeting its smart thermostat criteria. Most need a common wire, or C-wire, for steady power.
Why it matters to you
Setbacks while you sleep or are away reduce runtime, and runtime and alert data can flag a struggling system early. On heat pumps, a thermostat that is not set up correctly can call for auxiliary heat more often than needed.
Practical guidance
Before buying, check that your system has a C-wire or that the thermostat includes a power adapter, and photograph the old wiring before disconnecting it. For heat pumps, confirm the thermostat supports heat pump and auxiliary heat staging.