Emerson Sensi ST55
Score: 72/100
Amazon Smart Thermostat
Score: 73/100Rankings
The Amazon Smart Thermostat is an ENERGY STAR-certified, Alexa-focused thermostat with auto-learning temperature control and a compact touch-sensitive display. Its main trade-offs are the mandatory C-wire and limited 2.4 GHz Wi-Fi with no built-in voice mic. Ideal for Alexa/Ring users seeking an affordable, easy-install solution.
Emerson Sensi ST55 provides a 5-inch LED touchscreen, broad smart-home compatibility, and geofencing-driven energy savings, all at an affordable price. Limitations include the need for a C-wire, 2.4 GHz-only Wi-Fi, and lack of built-in room sensors. Ideal for DIY homeowners seeking a versatile, budget-friendly thermostat.
| Attribute | | |
|---|---|---|
3 yearsbest | — | |
5 inchbest | 0.9 inch | |
| ↓ lower better | 0.386 kg | 0.11 kgbest |
Click an attribute name to sort · Green = best, red = worst (relative to this comparison)
| Attribute | | |
|---|---|---|
General(1) | ||
HVAC Compatibility | Various (single to multi-stage) | 24V |
Connectivity(2) | ||
Wi‑Fi Standard | 802.11 a/b/g/n (2.4GHz) | 802.11 b/g/n (2.4GHz) |
Smart Home Integration | Alexa, Google Assistant, Apple HomeKit, Samsung SmartThings | Alexa, Ring |
Power & Installation(1) | ||
Power Source | 20-30 VAC | C‑wire (24V) |
Display(2) | ||
Display Type | LED touchscreen | Touch-sensitive |
Screen Size (inch) | 5 inch | 0.9 inch |
Build & Design(2) | ||
Device Weight (kg) | 0.386 kg | 0.1095 kg |
Device Dimensions (H×W×D) (mm) | 25.4×149.35×95.25 mm mm | 21.4×90.4×90.4 mm mm |
Products in the top-left offer the best value (high score, low price).
Professional reviewers commend the Sensi ST55 for its straightforward DIY installation, ENERGY STAR efficiency and the claimed 23% energy savings, as well as its compliance with Title 24 and robust smart-home integration. However, they point out the need for a c-wire to unlock full functionality and the limitation to a 2.4 GHz Wi-Fi band.
Homeowners and renters alike praise the thermostat's quick setup, remote app control, energy-saving reports, and reliable fan circulation. Recurring complaints focus on occasional Wi-Fi drops, the necessity of a c-wire for some systems, and the lack of a built-in room sensor or precise humidity control.
Professional reviewers consider the Amazon Smart Thermostat a strong value proposition, praising its auto-learning algorithm, tight Alexa integration, and broad 24V HVAC compatibility while noting its ecosystem constraints, mandatory C-wire, and limited connectivity as notable drawbacks.
Everyday users generally appreciate the straightforward Alexa-guided setup, reliable auto-scheduling, and remote app control that delivers noticeable energy savings, but they frequently cite the C-wire requirement and occasional cycling glitches as pain points.
“Easy Alexa-guided install (even with new C-wire)”
“Heats to 68°F home, drops to 52°F away”
