These are more common. In addition to the line and switched line, a neutral is also required. This is used to power a small heater inside the thermostat, to improve response times. Without this, the temperature difference between the thermostat switching On and Off (hysteresis) will be excessively large, resulting in the room temperature fluctuating significantly.

To reconnect the wire, simply put the wire on the right terminal and tighten down the set screw. Pull a wire a bit to make sure the wire is properly fixed. W wires go directly to the source of heating; that may be a furnace (gas, electric, oil, you name it) or heat pumps ( mini-split heat pumps included). The Nest 3rd Gen thermostat has 10 terminals, say Rh, Rc, W1, W2(aux) Y1, Y2, O/B, G, C, etc. You just need to connect ‘red’ wire from the furnace to Rh and ‘white’ wire to W1. These 2 connections will set the Nest thermostat as a ‘smart 2 wire thermostat’ taking care of your home heating ‘smartly’.

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Most thermostats do not require an earth connection, however an earth should still be provided at the thermostat position. The usual method is to provide 3 core and earth cable between the boiler and thermostat. This will allow either a 2 wire or 3 wire thermostat to be fitted.

B” is for reversing valve heating. Some producers like Rheem energizes the reversing valve when the heating mode is on in heat pumps. A dark blue “B” wire is needed for the t-stat terminal. Thermostat Green Wire (“G” Wire) Before we take the flathead screw to unscrew these, let’s first familiarize ourselves with the crucial part of any thermostat wiring: Wire codes and colors.

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To protect your equipment, turn off the power at the breaker box or switch that controls your heating and cooling. To confirm your system is off, change the temperature on your existing thermostat, so the system starts heating or cooling. If you don’t hear or feel the system turn on within 5 minutes, the power is off. You can skip this step if you have a digital thermostat with a blank display. O” or the orange thermostat wire is for reverse valve cooling. Most bigger heat pump manufacturers like Trane, Goodman, Lennox, and so on have the orange wire that goes to the condenser (located in the outdoor unit of heat pumps).

Great thermostat which I required for existing two wire supply, couldn't find one like it anywhere else. HVAC technicians know the color-coding by heart; they can just remove any Honeywell thermostat, replace it with the new one and reconnect the terminals.Remove the motherboard of the old thermostat completely, and secure the wires. You don’t want them to hide deep inside the wall. Very informative article. A comment and few questions (I am a ECE Prof / researcher with experience limited to few installations and so on). Question: I am a senior citizen who just moved into a rental home in Tucson and decided to go for the WiFi thermostat (free from TEP) but find the furnace is at the attic (with the control unit and the heat exchanger / air blower there) and the condenser coil for the AC on the outside of the home. I have no access to the manuals to know which system is in the house. The CT32 had five wires connected including the C wire but also uses 4 AA batteries and it’s manual says “the CT32 runs on 4 AA alkaline batteries and/or the C wire if Locate any unconnected wire labeled W or W1. If you identified an O, B, or O/B wire connecting to the O/B terminal in the previous step and it has a separate W wire, place it into the W2 terminal. Connect the W wire to the W terminal if you don’t have a wire connected to the O/B terminal.

If your O or B terminal shares a label with another wire — typically W —identify whether you have a heat pump system or not. A heat pump runs your compressor for both heating and cooling. If you don’t know your system type, place this wire in the W terminal. If you have a heat pump system, put it in the O/B terminal. Y2” is only for air conditioners with second-stage cooling. This terminal is only required if you have:In today’s world, more and more people are looking to save energy and money. One way to do this is by using a 2 wire smart thermostat. A two-wire best smart thermostat is a thermostat that can be controlled remotely, making it perfect for people who are always on the go. Additionally, a 2 wire smart thermostat can help you save money on your energy bill. Type of two-wire HVAC system I've had a shifty on t'net and Satchwells of this ilk seem to have common wiring terminals as follows: