Which one fits which system
Both are smart wifi thermostats from the same table; what separates them is c wire (maker), systems (maker). 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 ST75 Smart Thermostat lists Common wire (c-wire) is required.
Systems (maker). The Sensi ST55 Smart Thermostat lists Works with HVAC equipment found in most homes; the Sensi ST75 Smart Thermostat lists Works with the HVAC equipment found in most homes.
Statement by statement
| Statement | Sensi ST55 Smart Thermostat | Sensi ST75 Smart Thermostat |
|---|---|---|
| C wire (maker) | Common wire (c-wire) is not required in most applications | Common wire (c-wire) is required |
| 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, Apple HomeKit, Google Assistant, SmartThings, Vera |
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
Choose the Sensi ST75 Smart Thermostat if
- C wire (maker): Common wire (c-wire) is required
- Systems (maker): Works with the HVAC equipment found in most homes