Smart Thermostats / Copeland
Sensi Lite (ST25)
The cheapest truly C-wire-free thermostat — until you own a heat pump, and then it isn't.
Overall score 5.9/10
Pros
- + One of only three thermostats here that runs without a C wire on ordinary conventional systems, and by far the cheapest
- + Ten terminals including AUX and L, with dual-fuel and zone-valve support that no other sub-$100 model here documents
- + Copeland spells out the C-wire exception in the product title itself instead of burying it in a compatibility checker
- + $79 street against $89.99 list, with heavy utility-marketplace rebate availability
Cons
- − The C-wire exemption evaporates exactly where it matters: heat-only, cool-only and heat pump systems all need one
- − No Apple Home and no Matter, so it is Alexa, Google or the Sensi app and nothing else
- − No room sensor support at all — Copeland reserves Sensi Room Sensors for the Touch 2
- − No humidifier or ventilator terminals despite the generous terminal count
- − No trim plate and no battery backup — the manual states there is no battery option, so a blown 24V fuse leaves the screen dark
Sensi Lite (ST25) review: what the specs say
The cheapest truly C-wire-free thermostat — until you own a heat pump, and then it isn't. At $79, Copeland's 2023 model sits among the cheapest we cover — the smart Thermostats we compare run from $79 to $259.99. It scores 5.9/10 overall, calculated from published specifications across 8 categories rather than from a subjective impression.
Its strongest showing is Value at 9.0/10 — what the money buys once accessories, adapters and sensors are added in. The weakest is Multi-Room Sensing at 1.0/10, which is the trade-off to weigh before buying: if that is the specification you care about most, one of the alternatives below will serve you better.
Worth knowing before you buy: the C-wire exemption evaporates exactly where it matters: heat-only, cool-only and heat pump systems all need one; and no Apple Home and no Matter, so it is Alexa, Google or the Sensi app and nothing else. Every specification on this page comes from Copeland's own documentation or a verified retail listing — where a figure is not published, the table says so rather than estimating it.
Specifications and price last verified . Report an error
Full Specifications
| System Voltage | Low voltage 24VAC (20-30VAC, 50/60Hz). Not for 120/240V line-voltage heat |
| C-Wire Required | Mostly no — and Copeland is unusually honest about the exception. Its own product title reads 'C-Wire Not Required, Except On Heat/Cool Only and Heat Pump Systems', and the manual confirms heat-only, cool-only and heat pump systems all need a common wire |
| Adapter / Power Kit Included | No adapter is included, and none is needed on the majority of conventional systems |
| Heating & Cooling Stages | 2H/1C or 1H/2C, single and multi-stage, gas, oil or electric. Ten terminals: R, C, W/E, G, Y, O/B, Y2, W2, L and AUX, rated 1.5A per terminal and 2.5A total |
| Heat Pump & Aux Heat | Yes — heat pump 2H/1C, and the manual lists dual fuel and zone valve configurations. A heat pump does need a C wire on this model |
| Humidifier / Ventilator Terminals | None — no humidifier, dehumidifier or ventilator output |
| Remote Sensors | None. Copeland states only the Sensi Touch 2 works with Sensi Room Sensors |
| Occupancy Detection | None. Away control is geofencing from your phone only |
| Matter Support | No |
| Voice & Smart Home Platforms | Sensi app, Amazon Alexa, Google Assistant, Samsung SmartThings. No Apple Home |
| Utility Rebates & Demand Response | ENERGY STAR certified, rated for about 23% HVAC energy savings, and stocked across US utility rebate marketplaces |
| Account or Subscription Needed | No subscription. A free Sensi account is required |
| Connectivity | 2.4GHz Wi-Fi, Bluetooth LE |
| Material | Plastic housing with a glass touchscreen face |
| Warranty | 36 months |
Compare Sensi Lite (ST25) With
Premium Alternative
Honeywell Home X2S (RTH2CWF) — $79.99