ecobee

My thermostat has only two wires. Am I compatible with ecobee?

ecobee thermostats require a C (common) wire to power on. If your current thermostat uses only two wires (R and W, or T and T), there are a few installation options available, depending on your application.

Before getting started, please note the following:

  • You will not be able to install the Power Extender Kit (PEK) with heat-only 2-wire systems. The PEK can only be used on furnace or heat pump systems that do not have a C wire — this is because the PEK requires R (power), G (fan), and Y (compressor) wires to operate, and these 2-wire heat-only systems do not have these G and Y wires


  • To determine compatibility, you will need to access both the wiring at your thermostat as well as the wiring at your heating system where the thermostat wiring ends. If you are not comfortable doing so, you can reach out to ecobee support for guidance, or hire a technician to aid in installation


  • Depending on how many spare wires you have behind the wall at the thermostat, some of these options will require additional components that are not included with the ecobee, including running new wires and/or purchasing an external 24VAC transformer, SP/NO isolation relay, or Fast-Stat Common Maker

 

STEP 1:
DETERMINE HOW MANY THERMOSTATS YOU HAVE CONTROLLING YOUR HEATING SYSTEM

If you have one thermostat controlling your heating system, proceed to Step 2 below.

If you have two or more thermostats controlling your heating system, please click here for further instructions.

Remove your thermostat from the wall and look for any unused wires that are not currently connected to your thermostat. Be sure to check behind the wall at the thermostat as well. In some cases, the wire bundle at the thermostat will contain more than two wires total, with numerous unused wires available for use.

Note this number down and proceed to Step 3.

The next step involves verifying what your thermostat wires connect to at your heating equipment.

Note down the wiring colours at your thermostat and the types of terminals they are connected to. Next, locate your thermostat wires at your heating equipment. You'll need to locate the point in which the two low-voltage thermostat wires join up with your equipment.

Depending on the make and model of your equipment, your thermostat wires may connect to the following:

  • Wiring terminals such as R, W, and C at your furnace
  • A gas valve with terminals such as Th, Tr, and Th-Tr
  • T/T connections, often connected to an Aquastat

 

 

 

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If your thermostat wires connect to terminals marked R and W, installation is as simple as connecting a third wire to the common on the furnace or boiler's low-voltage Common point. Depending on your furnace, this may be either a terminal marked "C" or "Com 24V", or you may need to locate where the common can be connected to.

Every furnace and boiler that has a 24VAC transformer will have a common terminal—just trace the 2 low-voltage wires and see where they connect to. If there is an existing connection point, then tap the C wire coming from the thermostat at this point. Sometimes cutting/stripping the common wire for splicing the thermostat's C wire may also be required.

 

 

Simply connect the spare wire to the common connection point.

rwcdiagram.png

If you do not have any additional wires, you have two options:

  • Run an additional wire at your thermostat down to your equipment

OR

  • Purchase and install a Fast-Stat Common Maker

rwcfaststat.png

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An alternative solution is to power the ecobee with an external 24VAC plug-in transformer. This transformer can be plugged into a wall, and would be wired as follows:

  • The 24VAC transformer wires would connect to RC and C on the ecobee
  • The two wires on your old thermostat would connect to RH and W1 on the ecobee

NOTE: Ensure the transformer is capable of 24V AC output (not DC output)

 

 

 

gasvalve.png gas-valve.jpg

If your thermostat wires connect to terminals marked Th, Tr, and Th-Tr, they are likely connecting to a gas valve.

However, you will need to trace the wires connecting to the gas valve and follow them to the 24VAC transformer for the heating equipment to identify where your "C" connection will be. If you require assistance with this, please contact ecobee support.

Simply connect the spare wire to the common connection point.

gasvalvediagram.png

If you do not have any additional wires, you have two options:

    • Run an additional wire at your thermostat down to your equipment

gasvalvediagram.png

OR

  • Purchase and install a Fast-Stat Common Maker

gasvalvefaststat.png

 

24vactransformer.png

An alternative solution is to power the ecobee with an external 24VAC plug-in transformer. This transformer can be plugged into a wall, and would be wired as follows:

  • The 24VAC transformer wires would connect to RC and C on the ecobee
  • The two wires on your old thermostat would connect to RH and W1 on the ecobee

NOTE: Ensure the transformer is capable of 24V AC output (not DC output)

 

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If your thermostat wires connect to T/T terminals, note that you will require a separate 24VAC transformer to power the ecobee. You may also require additional components.

T/T connections often indicate a connection to a device known as an Aquastat.

 

If you have an extra wire, you will require an isolation relay and a separate 24VAC transformer.

ttwithisorelay.png

 

ecobee requires an isolation relay with a 24VAC coil and Normally Open (N/O) contacts.

 

If you have no extra wires, you'll need both a Fast-Stat Common Maker and a separate 24VAC transformer

ttwithfaststat.png

The Fast-Stat Common Maker is available at the Fast-Stat website.

 

24vactransformer.png

An alternative solution is to power the ecobee with an external 24VAC plug-in transformer. This transformer can be plugged into a wall, and would be wired as follows:

  • The 24VAC transformer wires would connect to RC and C on the ecobee
  • The two wires on your old thermostat would connect to RH and W1 on the ecobee

NOTE: Ensure the transformer is capable of 24V AC output (not DC output)

NOTE (2): Some T/T connections may not work reliably when connected directly to the Rh and W1 terminals of the ecobee. In that case, a 24 VAC transformer and isolation relay on the equipment side would be necessary (see details under "IF YOU HAVE AN EXTRA WIRE" above).

 

 

 

If you have two or more thermostats controlling your heating system:

If your heating system is controlled by more than one thermostat, your system likely has zone valves or a zone control relay.

Please reach out to ecobee support with the following information in order to determine compatibility and appropriate installation instructions:

  • How many thermostats you have in total for the heating system
  • Photos of the wiring at each thermostat
  • Photos of the wiring at any zone valves or zone boards
  • The make and model of each zone valve and/or zone boards
  • The number of extra wires that are behind the wall at each thermostat

If you are having difficulty identifying your zone valves or zone boards, some commonly used brand names for zone valves/zone control equipment include:

  • Taco
  • Honeywell
  • Erie
  • Energy Kinetics

 

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