Thermostats

Thermostats and thermostat accessories from Resideo, tekmar Control Systems, Southwire and DiversiTech. Resideo is the company that builds and sells the Honeywell Home line, so a thermostat listed by its Resideo number, such as TH6220WF, is the one sold at retail as the Honeywell Home T6 Pro — same part, two names. Families stocked here: PRO 1000, PRO 2000, PRO 3000 and CommercialPRO 7000; the T-series from T1 Pro through T10 Pro; FocusPRO 5000 and 6000; VisionPRO 8000; WiFi 9000; and Prestige IAQ.

Voltage decides the thermostat before anything else does. A low-voltage thermostat runs on 24V through the equipment transformer and is what gas furnaces, heat pumps, boilers and air handlers use. A line-voltage thermostat switches 120V or 240V directly and is for electric baseboard, electric radiant panels and fan-forced wall heaters. They are not interchangeable. Wiring a 24V thermostat to a 240V baseboard circuit is a fire risk, not a malfunction, and the mistake is easy to make because the two look alike on the wall.

Line voltage thermostats are stocked for electric heat, single-pole and double-pole, manual and 7-day programmable. Single-pole leaves one leg energized when the dial is off; double-pole breaks both. If the heater has to be fully dead at the thermostat, it has to be double-pole.

Millivolt is the third case and it catches people out. A standing-pilot wall heater or gas fireplace generates its own 750 mV from the thermopile and has no transformer at all; it needs a millivolt-rated thermostat, and a digital 24V unit will simply not close the circuit. Heat-only millivolt models are stocked for exactly this.

The C-wire is the most common reason a Wi-Fi thermostat replacement stalls. Older homes were wired with four conductors and no common, and a smart thermostat needs continuous 24V to run its display and radio. Either pull new cable or add an adapter — the Resideo WireSaver THP9045A1023 puts the common back at the equipment end without opening walls.

Resideo splits connected control two ways and they solve different problems. Wi-Fi models talk to the house router and the phone app: T6 Pro Smart, the Wi-Fi VisionPRO 8000, and the WiFi 9000 color touchscreen. RedLINK is Resideo’s own 900 MHz link between the thermostat and its own accessories — wireless indoor and outdoor sensors, equipment interface modules, remote modules and the TrueZONE adapter — and it works where there is no reliable Wi-Fi at the equipment. RedLINK modules and sensors are in RedLINK accessories. The T10 Pro and Prestige IAQ kits use both.

Southwire thermostat wire is stocked in 18/2, 18/4, 18/5 and 18/6, in 250 ft and 500 ft. Count the conductors against the system before ordering: a straight heat-cool job lives on four, a heat pump with auxiliary heat and a common wants six, and pulling the smaller roll is how a job ends up needing a C-wire adapter later.

Shop by type: non-programmable thermostats, programmable thermostats, smart and Wi-Fi thermostats, Honeywell Pro Series, RedLINK thermostats and thermostat accessories. Accessories cover cover plates for the PRO, FocusPRO, T-series and Prestige, thermostat guards and keys, remote indoor and outdoor sensors, and a 120V transformer.

Related: the full Resideo (Honeywell Home) catalog, connected home equipment, thermostatic radiator valves for room-by-room hydronic control, and heating controls.

Frequently asked questions

Are Honeywell Home and Resideo thermostats the same?

Yes. Resideo builds and supports the Honeywell Home line, so a Resideo part number such as TH6220WF is the same thermostat sold at retail as the Honeywell Home T6 Pro.

Do I need a low-voltage or a line-voltage thermostat?

Gas furnaces, heat pumps, boilers and air handlers use a low-voltage (24V) thermostat. Electric baseboard, convector and radiant floor heat use a line voltage thermostat rated for 120V or 240V. If the old thermostat is connected with heavy wires and wire nuts, it is almost certainly line voltage.

Do I need a C-wire for a Wi-Fi thermostat?

Most Wi-Fi thermostats need continuous 24V power from a common (C) wire. If the wall has no C-wire, a C-wire adapter such as the Resideo THP9045A1023 WireSaver adds one at the equipment without pulling new cable.