Sensi Smart Thermostat Review: Is the ST55 a Practical DIY Replacement?
Worth it—if your setup matches
Worth it or skip it?
Worth it if
- Your HVAC type, wiring, 24-volt AC setup, and available wall space match the ST55 requirements.
Skip it if
- You cannot yet verify your HVAC type, wiring, 24-volt AC requirement, or available wall space.
Key facts
Specified powerUse this as a compatibility checkpoint, not proof that every installation will match.
Thermostat dimensionsMeasure the available wall area before relying on the manufacturer’s same-space claim.
A conditional DIY fit
Choose it when your system is a listed HVAC type, your wiring and 24-volt AC requirements check out, and the wall space fits. If those details are unclear, verify them before buying.
Buy on AmazonBefore the old thermostat comes down
You stand at the wall with the old thermostat’s wires exposed, ready to compare them before making the swap.
Guidance, with conditions
The ST55 combines button controls with a built-in level, step-by-step app guidance, and included mounting hardware and documentation. Sensi says a common wire is not required in most applications, while the thermostat is specified for 24-volt AC systems and listed HVAC types.
That makes the ST55 a guided replacement—not a universal wiring match.
Before you choose
Does the ST55 require a common wire?
No, Sensi says a common wire is not required in most applications; check your exact wiring before installation.
What HVAC systems is the ST55 intended for?
The listed uses are air conditioners, boilers, furnaces, and heat pumps.
Can I install it myself?
Yes, Sensi describes built-in leveling and step-by-step app instructions for DIY installation, with mounting hardware and documentation included.
Full spec sheet
| Controller Type | Amazon Alexa, Apple HomeKit, Google Assistant, SmartThings, Vera |
|---|---|
| Additional Features | Data Privacy, Easy DIY Install, Energy Savings, Filter Indicator, Programmable |
| Specific Uses For Product | Air Conditioner, Boiler, Furnace, Heat Pump |
| Temperature Control Type | Programmable, Smart/Remote |
| Connectivity Technology | Wi-Fi |
| Power Source | Corded Electric |
| Voltage | 24 volts_of_alternating_current |
| Display Type | LED |
| Screen Size | 5 inches |
| Control Type | Button Control |
| Control Method | App, Touch, Voice |
| Connectivity Protocol | Wi-Fi |
| Mounting Type | Wall Mount |
| Number of Batteries | 2 AA batteries required. (included) |
| Color | White |
| Shape | Rectangular |
| Product Style | DIY |
| Material Type | Plastic |
| Finish Types | Glossy |
| Brand Name | Sensi |
| Model Name | ST55 |
| Included Components | Thermostat, free mobile app, 2 AA batteries, mounting hardware, wire stickers, installation guide, welcome guide with Sensi code, warranty booklet |
| Model Number | ST55 |
| Number of Items | 1 |
| Unit Count | 1 Count |
| Item Type Name | , Works with Alexa, Energy Star Certified |
| Manufacturer Part Number | ST55 |
| Item Dimensions D x W x H | 1"D x 5.88"W x 3.75"H |
| Brand | Sensi |
| Product Dimensions | 1"D x 5.88"W x 3.75"H |
| Special Feature | Data Privacy, Easy DIY Install, Energy Savings, Filter Indicator, Programmable |
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