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C-Wire Check: product guides
Read the full C-Wire Check buying guide.
| Product | Best for | Main strength | Main caveat |
|---|---|---|---|
| Sensi Smart Thermostat ST55 | Conventional or heat pump systems up to two stages, on a 2.4GHz network, in the old thermostat's footprint | Handles two-stage heat and two-stage cool, heat pumps and two-transformer systems at an entry price | The manual requires a common wire on heat-only, cool-only and heat pump systems, and no adapter is included |
| Google Nest Thermostat (Charcoal) | Single-stage 24V systems that need a schedule and app control, not multi-stage equipment | Works without a C wire in most homes, on either 2.4 GHz or 5 GHz Wi-Fi | Only one extra stage: no two-stage heat plus two-stage cooling, and no multi-stage heat pump support |
| Mysa Smart Thermostat V2 for Electric Baseboard Heaters (BB.2.0.01.NA-US) | 120V or 240V electric baseboard, fan-forced convector and radiant ceiling heat in a standard gang box | One of the few smart thermostats that actually runs 120V and 240V electric resistance heat | Useless on any 24V system: no furnace, heat pump, central boiler or millivolt fireplace support |
| ecobee Smart Thermostat Premium with SmartSensor | 24 VAC forced-air, heat pump, boiler or PTAC systems, checked first with ecobee's compatibility tool | SmartSensor, Power Extender Kit and trim plate are all included, not add-ons | The warranty excludes units not installed by a licensed HVAC contractor, while the listing sells DIY installation |
| Google Nest Learning Thermostat (4th gen) with Nest Temperature Sensor (2nd gen) | Multi-stage 24V systems run through the Google Home app, in homes with or without a C wire | Maker publishes the exact stages and terminals, including three-stage heat, cool and heat pump support | Setup requires the Google Home app and account; Alexa or Apple control goes through Matter and may need a third-party hub |
| ecobee Smart Thermostat Essential (EB-STATE7-01) | Simple single-transformer systems with one stage of cooling, on a 2.4GHz network | ecobee publishes the exact terminal list and stage support, so you can check fit before buying | Six terminals only: no two-transformer wiring, no second cooling stage on a heat pump, no accessory terminal |
See every side-by-side comparison.
- Sensi Smart Thermostat ST55
Sensi ST55 guide: the ten terminals and system configurations in the maker's manual, when a common wire is required, 2.4GHz-only Wi-Fi and the three-year warranty.
- Google Nest Thermostat (Charcoal)
Google Nest Thermostat guide: the one-and-a-half stages it controls, when Google says you still need a C wire, AAA backup batteries and two plates sold separately.
- Mysa Smart Thermostat V2 for Electric Baseboard Heaters (BB.2.0.01.NA-US)
Mysa for Electric Baseboard Heaters V2 guide: the 1,900W and 3,800W load ceilings, the 250W floor, what line-voltage wiring it needs, and a five-year warranty.
- ecobee Smart Thermostat Premium with SmartSensor
ecobee Smart Thermostat Premium guide: 24 VAC systems it supports, the included Power Extender Kit's own wire rules, dual-band Wi-Fi and a warranty clause to read.
- Google Nest Learning Thermostat (4th gen) with Nest Temperature Sensor (2nd gen)
Nest Learning Thermostat (4th gen) bundle guide: the stages Google says it controls, the C-wire exception, Matter-based control, and three different warranty terms.
- ecobee Smart Thermostat Essential (EB-STATE7-01)
ecobee Smart Thermostat Essential guide: six wire terminals, single-stage cooling limits, 2.4GHz-only Wi-Fi, and the two parts ecobee sells separately for install.