What You Need to Know About Heaters and Thermostats: Voltage and Circuit Capacity

By mark_watola on 11/12/2020


Thermostat voltage flowchart

Are you looking to replace a heater or thermostat? Wondering if the new heater is compatible with your current breaker and thermostat?

Many considerations go into checking heater and thermostat compatibility so let’s break down the different requirements into segments.


One of the first steps to determine thermostat and heater compatibility is checking voltage. Voltage depends on how the space is wired. Usually a space fits 120V or 240V. Check the room voltage on the breaker.


Most hardwired heaters use a maximum voltage of 120V or 240V. Purchasing the wrong heater can be dangerous. Before buying a heater, make sure you know the voltage of your space.


Line voltage thermostats can handle up to 120V or 240V. Line voltage is common in electric baseboard heaters, radiant heaters, and convection heaters. If the heater matches your home and thermostat voltage, it is ready to install and use. For line voltage, a single pole thermostat uses two wires, and a double pole thermostat requires four wires.

Most residential spaces employ low voltage thermostats, typically 24V. In this case, a transformer is required due to the voltage difference. Some models may also need a circuit relay. Low voltage thermostats apply thin wiring from 2 to 7 wires, depending on cooling or heat pump attachments.

WARNING: Failure to properly connect thermostats, heaters, and power sources can be dangerous. We recommend calling a licensed electrician for all wired installations.

How do I check the voltage of my thermostat?

Check the voltage of your thermostat in multiple ways:

  • Search Google for your thermostat’s make and model.
  • Check the manual or product label of your thermostat.
  • Use a multimeter to check the “C” wire’s voltage.
  • Call the thermostat manufacturer if you cannot determine the voltage.

Circuit Capacity

Thermostats come as either single pole or double pole. A single pole thermostat has no power cutoff. Because a single pole thermostat uses one circuit to power off an attached heater, you must unplug or disconnect it from the power supply.

If you wish to completely turn off your heater using your thermostat, a double pole thermostat can do this with the “off” switch as it utilizes two circuits in the circuit breaker.

How do I determine if my thermostat is single pole or double pole?

Look for an “Off” setting. If there is none, check the wiring. Generally, a single pole thermostat includes two wires, and a double pole thermostat requires four wires.

Most electric heaters can pair to either type of thermostat but verify the heater is compatible before purchasing.

If you would like to know more about heaters and thermostats, check out our blog.

How To Install A Single Pole Or Double Pole Thermostat To A 240V Baseboard Heater

The Difference Between Line Voltage And Low Voltage Thermostats

The Difference Between Single Pole And Double Pole Thermostats

A Buyer’s Guide To Heaters: 120V Vs. 240V