Thermostats & Their Terminal Letters – What to Know

The Heating, Ventilation, and Air Conditioning (HVAC) system serves to provide you and your family with the right temperature and the utmost comfort at home. When it comes to this, it’s important to know each component of your system and know how they work. When they start to wear and tear, you need to get them immediately inspected and repaired if necessary to ensure your heating and cooling system works as efficiently and smoothly as possible.

One key component of your entire HVAC system is the thermostat. In this article, we’ll share what you need to know about it, how it works, and what the terminal letters mean.

What a thermostat is

Simply put, a thermostat is a device installed in your HVAC system used to control the temperature. It essentially allows you to monitor and adjust the settings. Whether the settings are for cooling or heating the indoor area. At times, it can be set for a programmed schedule. A schedule allows your heating and cooling systems to turn on and off at certain set periods. It works by sensing your physical system’s temperature and performing certain actions to maintain the temperature near a desired setpoint. A schedule saves you money by giving you heating and cooling when you need it.

How a thermostat works

A thermostat is wired to your furnace or air conditioner, which typically acts as a switch to turn your unit on and off. It consists of some markings on it to identify the heating or cooling connection, fan connection, and heat pump connection, if applicable. It also has a terminal supplying power to each function for them to run efficiently. 

Furthermore, your thermostat works based on the temperature setting and/or programmed time schedule, providing the needed hot or cold air. In most cases, it is operated on 24-volt power supplied by a transformer. While it is generally safe to work without shutting the system off, it’s still best to do so for safety precautions.

What the thermostat terminal letters mean

Now, let’s take a look at the terminal letters to know what they stand for and what each terminal controls. Take note of the following terminal letters:

  • G: This terminal regulates the fan relay responsible for turning the blower fan on and off, either automatically or manually.
  • RC: This terminal is the 24-volt cooling power supply.
  • RH: This terminal is the 24-volt heating power supply.
  • Y/O: This terminal controls the cooling condenser by sending signals to power up the condenser and the blower fan.
  • W/B: This terminal controls the heat relay or valve by sending signals to power up the furnace and the blower fan or the boiler.
  • Y1: This terminal is used for the compressor contact in a single-stage heat pump installation.

It’s vital to know what these letters represent, so you know what they are for when the need arises. From there, you can make the necessary setting adjustments for your heating or cooling needs to make vital changes.


At this point, you now know what a thermostat is and how it works. To that end, be sure to get well-acquainted with the terminal letters. Understand what they mean so that you can adjust the settings. When your thermostat starts acting up, make sure to get it fixed or replaced as soon as possible. Hire the HVAC experts at Legacy to make a world of difference!

Are you looking to install or replace your thermostat? You’ve come to the right place, as Legacy Heating and Cooling offers the best heating and air conditioning services in Edmonton, AB and the surrounding area. If you’re looking to have expert HVAC maintenance, repair, or installation, get in touch with us today to see how we can help!

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