C-Wire Check product guide
Sensi Lite Smart Thermostat ST25 (Black)
Single-stage or one-extra-stage 24 VAC systems on a 2.4 GHz network
Copeland's Sensi Lite thermostat, confirmed by matching UPC. It handles 1H/1C, 1H/2C or 2H/1C conventional systems and 2H/1C heat pumps. Copeland and the listing agree that heat-only, cool-only and heat pump systems need a C wire. Setup requires the Sensi app and an account; the warranty is three years for DIY or pro installs.
Listing checked . Confirm the model, included parts and availability before ordering.
Published specifications
- Maker: stages 1H/1C, 1H/2C or 2H/1C conventional; heat pump 2H/1C; 3-wire zone heat
- Maker and listing: C wire required for heat-only, cool-only and heat pump systems
- Maker: 24 VAC, 20-30 Vac rating; hardwire with power stealing; 2 x AAA included
- Guide: Wi-Fi 2.4 GHz only; Sensi app and account required; Alexa, Google Assistant, SmartThings
- Maker: 5.07 x 3.13 x 0.88 in; 7-day schedule, 8 periods a day; geofencing; keypad lockout
- Maker warranty table: 3 years, DIY or professional install
Fit and limits
Strengths
- Listing and maker agree on exactly which systems need a C wire
- Three-year warranty applies whether you or a contractor installs it
- UPC matches Copeland's product page, which publishes a specification block
Caveats
- Only one extra stage: no 2H/2C, and no two-stage heat pump support
- Heat pump, heat-only and cool-only systems need a C wire
- Requires the Sensi app, an account and a 2.4 GHz network to set up
What the ST25 is, and what comes in the box
The Sensi Lite ST25 is a Wi-Fi thermostat sold under Copeland's Sensi brand, with a backlit LCD that Copeland lists at 2.25 square inches, and overall dimensions of 5.07 inches long, 3.13 inches high and 0.88 inches deep. Copeland's product page shows the same UPC as the Amazon listing, 786710568732, and both give the model as ST25.
Copeland's box list is the thermostat, instructions, mounting hardware, two AAA batteries and wire labels, and the Amazon Included Components field agrees. Copeland lists battery life of up to two years. It also lists a common-wire kit (SA11) and matching wallplates as related products, which are separate items and not in this box.
One extra stage, and only one
Copeland's specification lists single stage (1H/1C), multi-stage as either 1H/2C or 2H/1C, and heat pump as 2H/1C. The installation guide says the same thing in its own words: a conventional system can have multi-stage heating or multi-stage cooling, not both, and multi-stage is not available for heat pump configurations beyond the auxiliary or emergency heat stage.
Copeland also lists 3-wire zone heat, conventional air conditioning, gas, oil and electric heat, and heat pump among its applications, with terminals R, C, W/E, G, Y and O/B. If your equipment has two stages of both heat and cooling, or a two-stage heat pump, the ST25 is outside what Copeland claims. Run Sensi's compatibility check with your own wires before buying; we do not give wiring steps here.
The C-wire answer depends on your system type
The Amazon bullet says a common wire is required for heat pump and heat-only or cool-only systems and not required on most systems. Copeland's product page footnote names the same three cases, and the installation guide's wiring pages repeat that a common connection is required on heat-only, cool-only or heat pump systems. On this model the listing and the maker agree.
So a heat pump owner without a C wire should plan for one before buying. Copeland lists power as hardwire with power stealing, AAA batteries included, and an electrical rating of 20 to 30 volts AC. Neither the product page nor the installation guide mentions line-voltage or millivolt systems; everything is framed as 24 VAC, so confirm your system type with Sensi's checker.
App, account and Wi-Fi requirements
The installation guide is direct: to install and configure the thermostat correctly you must use the Sensi app, and you must create an account with an email address, to which the thermostat is linked once registered. The app also asks for Bluetooth and location permissions during setup. Anyone with that email and password can control every thermostat on the account.
The guide says Sensi is only compatible with 2.4 GHz networks and tells you to confirm your network before starting. Copeland's specification lists Wi-Fi 2.4 GHz and Bluetooth Low Energy, alongside a line reading 802.11 a/b/g/n supported. Take the guide's instruction and use a 2.4 GHz network. Copeland lists Amazon Alexa, Google Assistant and Samsung SmartThings as compatible platforms.
What the Sensi app does, and the privacy line
Copeland lists seven-day programming with up to eight periods a day, geofencing, a keypad lockout, smart alerts and service reminders for filters, humidifier pads and UV bulbs. The listing states about 23 percent HVAC energy saving; Copeland's footnote explains how that figure was derived and says savings vary.
The listing and the maker both state that Sensi will not sell your personal information or use thermostat activity data for advertising. Copeland's footnote adds that if you join a third-party programme, such as a utility scheme, that programme's terms and data collection are between you and the third party. Nothing we read describes a subscription for the thermostat's core features.
Warranty: three years whoever installs it
Copeland's warranty table lists ST25 among its DIY models with a three-year warranty whether a professional contractor installed it or you did it yourself. That matches the Amazon warranty field. The five-year term in the same table is reserved for listed Pro models bought and installed through a professional contractor, which does not include ST25.
We did not read the full written warranty terms for this model, only Copeland's summary table, so ask Sensi for the written terms before relying on details such as remedy or proof of purchase. The installation guide lists Sensi support at sensihelp.com for installation problems and questions about compatibility.
Check the current listing
Confirm the model, included parts and availability before ordering.
Primary sources
- Copeland product page and specifications for Sensi Lite Smart Thermostat ST25
- Sensi Lite installation guide R-5664 (ST25 series) supplied with the Amazon listing
- Copeland Sensi warranty table by model
Primary sources checked .
Compare with
- Sensi Smart Thermostat ST55
Conventional or heat pump systems up to two stages, on a 2.4GHz network, in the old thermostat's footprint
- Google Nest Thermostat (Charcoal)
Single-stage 24V systems that need a schedule and app control, not multi-stage equipment
- Mysa Smart Thermostat V2 for Electric Baseboard Heaters (BB.2.0.01.NA-US)
120V or 240V electric baseboard, fan-forced convector and radiant ceiling heat in a standard gang box
- ecobee Smart Thermostat Premium with SmartSensor
24 VAC forced-air, heat pump, boiler or PTAC systems, checked first with ecobee's compatibility tool
- Google Nest Learning Thermostat (4th gen) with Nest Temperature Sensor (2nd gen)
Multi-stage 24V systems run through the Google Home app, in homes with or without a C wire
- ecobee Smart Thermostat Essential (EB-STATE7-01)
Simple single-transformer systems with one stage of cooling, on a 2.4GHz network
Side-by-side pages, this model next to: Sensi Touch 2 Smart Thermostat ST76 (Black), ecobee Smart Thermostat Essential (EB-STATE7-01), Google Nest Learning Thermostat (4th gen) with Nest Temperature Sensor (2nd gen).