About Us
ThermostatWires is a free, independent technical resource built to take the guesswork out of smart thermostat installations and residential home wiring.
Why We Built ThermostatWires
Installing a smart thermostat should be one of the most rewarding home improvements you can make: it saves energy, enhances comfort, and integrates with modern smart home ecosystems. Yet for many homeowners, the wiring is where it gets stuck:
- Inconsistent Wire Colors: While HVAC textbooks suggest standards, real-world installers frequently used whatever wire was on the truck. A blue wire might be C, but on another system it could be O/B, Y, or Aux.
- Manufacturer Bias: When you use a single brand’s compatibility checker, it only shows you whether their specific unit works—often failing to explain workarounds, adapter modules, or whether an alternative brand would be a direct swap without running new cables.
- The Missing C Wire: Many older homes have no dedicated common (C) wire, leaving homeowners choosing between plug-in adapters, power extender kits, wire savers, and power-stealing thermostats.
We built ThermostatWires to provide one universal, unbiased reference tool where you enter your old thermostat's terminal letters once and instantly see the exact wiring diagram, compatibility verdict, and adapter requirements across the Google Nest Learning Thermostat (4th gen), ecobee Smart Thermostat Premium and Enhanced, Honeywell Home T9, and Amazon Smart Thermostat side by side.
How Our Verification Engine Works
Our compatibility engine checks your wire terminals against the manufacturers’ published wiring documentation, including:
- Google’s Nest wire-label and compatibility help pages for the Nest Learning Thermostat (4th gen)
- ecobee’s installation guides and Power Extender Kit (PEK) wiring for the Smart Thermostat Premium and Enhanced
- Resideo / Honeywell Home T9 supported-label documentation, including the wire-saver K terminal and Rh/Rc dual transformers
- Amazon’s Smart Thermostat wiring help and C-wire power adapter instructions
- For the home wiring diagrams: common National Electrical Code (NEC) residential practice, such as re-marking white wires used as hots
The engine handles single-stage and multi-stage heating and cooling, heat pumps with O or B reversing valves, auxiliary electric strip heating, emergency heat, dual-fuel configurations (heat pump with gas/oil furnace backup), and dual-transformer systems with independent heating and cooling power supplies.
Interactive Home Wiring Simulator
In addition to our thermostat wiring tool, we publish interactive home wiring diagrams covering light switches, 3-way and 4-way circuits, dimmers, GFCI outlets, ceiling fans, and video doorbell transformers. Unlike static diagrams, each circuit runs in a simulator you can flip switch by switch, and every setup is automatically tested for shorts, correct hot/neutral polarity, and grounding.
Our Commitment to Safety
Safety is built into every layer of our tools. If you tell the tool you have signs of 120V or 240V line-voltage heating (such as thick conductors joined with wire nuts, or electric baseboard heaters), it shows a prominent safety warning advising users that standard smart thermostats are incompatible and dangerous on high-voltage circuits. It also flags proprietary communicating systems (such as Carrier Infinity or Lennox iComfort) and millivolt gas heaters.
Who runs ThermostatWires
ThermostatWires is an independent project run by Ismail Farooq, a sole proprietor based in Lahore, Pakistan. I build and maintain the wiring tool, the diagrams and the guides myself. I’m not an HVAC technician or a licensed electrician, which is why every mapping on this site is taken from the manufacturers’ own installation guides and support pages listed above rather than from personal opinion, and why the guides tell you to stop and call a professional whenever a setup is unusual or involves line voltage.
When a manufacturer changes its documentation, or a reader reports a setup the tool gets wrong, I check it against the official guide and update the rules. You can reach me at [email protected].
How the guides and tools are made
- Wiring rules are written by hand from the manufacturers’ documentation and checked by an automated test suite on every change: each thermostat’s rules are tested against the manufacturers’ published cases, and every home wiring diagram is run through a circuit simulator for every switch position to catch shorts, reversed polarity and missing grounds.
- Guides are fact-checked against the sources above before publishing. When a reader points out an error, it is corrected and the page’s “updated” date changes.
- The photo reader uses an AI vision model to read terminal letters from your photo. It can misread labels, so the tool always shows what it read and lets you correct it before giving a result.
Editorial Independence & Transparency
ThermostatWires is independent and is not owned, operated, or sponsored by Google LLC, ecobee Inc., Resideo Technologies, Amazon.com, Ring LLC, or Lutron Electronics. All compatibility grades and wiring instructions are generated by deterministic algorithmic rules—never altered by commercial sponsorships or advertising partnerships.
We fund hosting and development through display advertising from Google AdSense and Amazon Associates affiliate links. When you buy something through our Amazon links, we may earn a commission at no extra cost to you.
Feedback & Continuous Improvement
We actively maintain our wiring logic as new smart thermostats and HVAC equipment enter the market. If you are an HVAC technician, electrician, or homeowner and notice a rare wiring configuration or discrepancy, please contact us. Corrections are checked against the official documentation before they go live.
The same maker also runs SongUp AI, ImgVX AI, The Net Fix, MxMob and A DIY Day; see our other projects.