Best Smart Thermostats

We reviewed smart thermostats across learning algorithm accuracy, app interface clarity, compatibility with multi-stage HVAC systems, energy reporting detail, and ease of installation for DIY versus professional setup.

C-wire requirement is the most common installation surprise. Smart thermostats require continuous power from the common wire in the HVAC wiring. Many older homes were wired without a C-wire, requiring either running a new wire, using a power adapter kit, or buying a thermostat specifically designed for C-wire-free installation. Check your existing wiring before buying to avoid installation problems.

Compatibility with your specific HVAC system type is non-negotiable. Single-stage systems work with most smart thermostats. Multi-stage systems, heat pumps, and radiant heat systems have specific compatibility requirements. Every smart thermostat manufacturer provides a compatibility checker -- use it with your existing wiring diagram before purchasing.