EcoGuide · Smart Thermostats · Updated 2026-09-29 · 1,000 words
Best Cheap Smart Thermostats Under $100
The Short Answer
| Pick | Best for | C wire | Heat pump |
|---|---|---|---|
| Sensi Lite (ST25) | Most homes, especially without a C wire | Not needed on most systems | Up to 2 heat / 1 cool (needs a C wire) |
| Honeywell Home T5 | A touchscreen and geofencing | Required | Up to 3 heat / 2 cool |
| Amazon Smart Thermostat | Alexa households | Required (or an adapter) | Check Amazon’s compatibility checker |
You are not giving up savings by buying cheap. ENERGY STAR puts the average for certified smart thermostats at about 8% of heating and cooling bills, around $50 a year, and that comes from scheduling and away modes, which all three have. The extra money on premium models buys room sensors, better heat pump controls and nicer screens.
How we chose: manufacturer specifications and support pages, linked throughout. We do not test products in-house. “Under $100” is based on Amazon prices checked in September 2026; prices move, so check the listing.
1. Sensi Lite (ST25): Best Overall Under $100
The easiest cheap thermostat to install in an older home. Sensi says the Lite works without a C wire on most systems, running on two AAA batteries; the exceptions are heat-only, cool-only and heat pump systems. Sensi says all its thermostats are ENERGY STAR certified, and its comparison page lists Alexa support and heat pumps up to 2 heat / 1 cool.
Skip it if: you want room sensors (it does not support them) or a colour touchscreen.
We may earn a commission if you buy through these links, at no extra cost to you. Products are chosen on published specifications; we do not test them in-house (how we choose).
Sensi Lite Smart Thermostat (ST25)
No C wire needed on most systems; ENERGY STAR; works with Alexa.
View on Amazon2. Honeywell Home T5: Best Touchscreen
A straightforward touchscreen with 7-day scheduling and geofencing. Honeywell lists it as ENERGY STAR certified, working with Alexa, and supporting heat pumps up to 3 heat / 2 cool — the widest heat pump support on this list.
Skip it if: you have no C wire. The Amazon listing for this version says a C wire is required. Honeywell also marks some T5 versions as discontinued on its site, so buy while it is in stock.
We may earn a commission if you buy through these links, at no extra cost to you. Products are chosen on published specifications; we do not test them in-house (how we choose).
Honeywell Home T5 Smart Thermostat (RTH8800WF2022)
Touchscreen; 7-day scheduling and geofencing; ENERGY STAR; C wire required.
View on Amazon3. Amazon Smart Thermostat: Best for Alexa
Built on Honeywell Home (Resideo) technology and, per Resideo, ENERGY STAR and UL ECOLOGO certified. You set it up and run it entirely from the Alexa app. Amazon says it emails details of available energy-provider rebates after purchase.
Skip it if: you have no C wire (Amazon lists it as C-wire required) or you want room sensors. Note that the listing below is a 2-pack, so the total is higher than a single thermostat. Setup trouble? See how to reset an Amazon Smart Thermostat.
We may earn a commission if you buy through these links, at no extra cost to you. Products are chosen on published specifications; we do not test them in-house (how we choose).
Amazon Smart Thermostat
Runs from the Alexa app; ENERGY STAR certified; C wire required. This listing is a 2-pack.
View on AmazonWorth Stretching Past $100?
Two models sit just above the line and fix the budget picks’ biggest gaps:
- Google Nest Thermostat ($129.99 from Google): works without a C wire on most conventional systems, but heat pumps need a C wire or Power Connector, and it does not support room sensors.
- ecobee Smart Thermostat Essential ($139.99 from ecobee): 3-year warranty and compatible with ecobee SmartSensors, but needs a C wire or the separately sold Power Extender Kit.
Compare them properly in ecobee vs Nest.
Before You Buy: Three Checks
- C wire. Take the old thermostat off the wall (power off) and look for a wire on a C terminal. No C wire? The Sensi Lite is the simplest option; see thermostats that work without one.
- System type. Heat pumps, heat-only boilers and multi-stage systems narrow the choice. Note the labels on your existing wires.
- Rebates. Many utilities discount smart thermostats. Check your utility’s website before buying; programmes change year to year.
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Frequently Asked Questions
What is the best smart thermostat under $100?
For most homes, the Sensi Lite: it works without a C wire on most systems, is ENERGY STAR certified and works with Alexa. Choose the Honeywell Home T5 for a touchscreen and wider heat pump support, or the Amazon Smart Thermostat for an Alexa home.
Will a cheap smart thermostat save as much as an expensive one?
Mostly, yes. The savings come from scheduling and away modes, which budget models have. ENERGY STAR’s average for certified models is about 8% of heating and cooling bills, around $50 a year.
Do cheap smart thermostats need a C wire?
Some do. The Honeywell T5 and Amazon Smart Thermostat need one; the Sensi Lite does not on most systems, though it does for heat pumps.
Do budget smart thermostats work with heat pumps?
Yes, within limits: the Honeywell T5 supports up to 3 heat / 2 cool and the Sensi Lite up to 2 heat / 1 cool. For heat pumps with electric backup, a thermostat with an aux heat lockout is worth the extra money.
Related Guides
- Best smart thermostat without a C-wire — for older wiring
- Best smart thermostat for Alexa — for Echo households
- Ecobee vs Nest — the premium options
- Smart thermostat savings calculator — payback on your numbers
