This will serve as a reference in the event you lose track of the terminal any wire was connected to. Take a picture of the old wiring connected to the various terminals.Turn off the electrical circuit to the furnace or air handler.If you haven’t changed your HVAC system components but want a new thermostat, take this approach. If the old thermostat has been removed, then the approach is a bit more complex but can still be a DIY project. If the old thermostat is still installed, then this will work. Millivolt furnaces that do not require electricity.Solid fuel stoves (wood, pellets, corn, anthracite, coal and other biomass materials).The following systems ARE NOT 24-volt systems: More than 90% of all HVAC (Heating, Ventilation, Air Conditioning) systems are low voltage 24V systems. Dual fuel systems with a furnace and heat pump are 24-volt / low-voltage systems. They can be single-stage, two-stage or variable-capacity systems. These systems can be traditional split systems, with one component outside and others inside, ductless split systems with outside and inside components and packaged systems with all components located in a single large case, usually installed outdoors.

Accessories: Humidifier, dehumidifier, ERV/HRV ventilator, air purifier and other air quality equipment.Cooling: Air conditioner, PTAC (packaged terminal air conditioner), heat pump.Heating: Gas furnace, either natural gas (NG) or propane (LP), oil furnace, heat pump with or without auxiliary heat strips.Most are used for supplemental heat or space heating.įeel free to jump to the section that covers your specific topic:Ģ4V or low-voltage heating and cooling systems include one or more of these components: Millivolt power: These are gas-fired heaters that don’t use electricity because they don’t have a blower fan.110V or 240V power: These are called high-voltage or line-voltage systems and include electric furnaces and electric baseboard systems.Note that only 24-volt wiring is covered: We do not cover 110/240-volt thermostat wiring and millivolt thermostat wiring issues.Īs the Pick HVAC Thermostat Buying Guide says about these thermostats of alternate voltage: No matter if your thermostats are from third-party brands like Honeywell, Nest, Sensi, White Rodgers or Ecobee, or the same brands (Trane, Carrier, Goodman, etc.) as your HVAC systems, this guide will help familiarize you with the wiring process. This complete 24-volt thermostat wiring guide covers all thermostat wiring issues from the simple to the complex – from basic 2 wire thermostat wiring common to gas furnaces all the way to 8 wire thermostat wiring for two stage heat pumps and similar HVAC systems.

Ac transformer wire color code