Both are smart wifi thermostats from the same table; what separates them is c wire (maker), systems (maker), works with. Pick by the one your wiring and system need, using the rows below.
The central trade-off
C wire (maker). The Sensi ST55 Smart Thermostat lists Common wire (c-wire) is not required in most applications; the Sensi ST25 Smart Thermostat lists COMMON WIRE REQUIREMENTS: Designed to work without a C-wire in most homes, but for some sys.
Systems (maker). The Sensi ST55 Smart Thermostat lists Works with HVAC equipment found in most homes; the Sensi ST25 Smart Thermostat lists Works with the HVAC equipment found in most homes.
Works with. The Sensi ST55 Smart Thermostat lists Amazon Alexa, Apple HomeKit, Google Assistant, SmartThings, Vera; the Sensi ST25 Smart Thermostat lists Amazon Alexa, Google Assistant, Hand Control, SmartThings.
Statement by statement
| Statement | Sensi ST55 Smart Thermostat | Sensi ST25 Smart Thermostat |
|---|---|---|
| C wire (maker) | Common wire (c-wire) is not required in most applications | COMMON WIRE REQUIREMENTS: Designed to work without a C-wire in most homes, but for some sys |
| Heat pump (maker) | Not stated by the maker | Not stated by the maker |
| Stages (maker) | Not stated by the maker | Not stated by the maker |
| Systems (maker) | Works with HVAC equipment found in most homes | Works with the HVAC equipment found in most homes |
| Sensors | Not stated by the maker | Not stated by the maker |
| Works with | Amazon Alexa, Apple HomeKit, Google Assistant, SmartThings, Vera | Amazon Alexa, Google Assistant, Hand Control, SmartThings |
Values are the makers' published specifications. "Not stated" means the maker doesn't publish it.
Which should you choose?
Choose the Sensi ST55 Smart Thermostat if
- C wire (maker): Common wire (c-wire) is not required in most applications
- Systems (maker): Works with HVAC equipment found in most homes
- Works with: Amazon Alexa, Apple HomeKit, Google Assistant, SmartThings, Vera
Choose the Sensi ST25 Smart Thermostat if
- C wire (maker): COMMON WIRE REQUIREMENTS: Designed to work without a C-wire in most homes, but for some sys
- Systems (maker): Works with the HVAC equipment found in most homes
- Works with: Amazon Alexa, Google Assistant, Hand Control, SmartThings