Heat Pump Thermostat Wiring Made Simple

• Find the disconnect switch to your air handler or furnace, and switch it off. This will be located near the unit.
• Shut off the circuit breaker at your home’s electrical panel if you can’t find the disconnect switch, or it’s difficult to access. You can also turn off the main breaker.
• Read the instructions and wiring diagram that came with your new thermostat, and keep them handy throughout the next steps.

Verify the wiring

• Remove the faceplate on the existing thermostat. Often you can pop off the faceplate, but you may need to remove a couple of screws.
• Use a non-contact voltage tester to check that there is no power coming to the thermostat.
• Count the number of wires attached to your old thermostat. “Verify that there are at least five wires available for use in your new thermostat,” Sherman says.
• Take a picture of the wiring so you know what wire goes where.

Remove the old thermostat

• Using a small screwdriver, remove the wires from the terminal block. Make sure you have taken a picture, to identify later where they were attached.
• Label each wire with a small piece of tape and marker as you remove them, if desired.
• Unscrew the mounting screws that attach the thermostat to the wall, and remove it.

Attach the new thermostat

• Thread the thermostat wires through the new thermostat base.
• Level the thermostat base and screw it into the wall using the hardware provided.
• Attach the thermostat wires to the new terminal block, following the wiring diagram and your photo.
• Match the colors precisely. “The wire color in the thermostat most often used for the heat pump is the orange wire,” Sherman says. “However, the wire color can vary slightly per different HVAC manufacturers.”

Wrap up the project

• Verify that your heat pump thermostat wiring is properly attached, according to the wiring diagram. “Make sure the wires are tight and all the way in the new thermostat,” Sherman says.
• Attach the faceplate.
• Turn on the power.
• Set up your new thermostat, adjusting and testing the AC, heat, auxillary heat and fan.

FAQs

What’s the difference between a heat pump thermostat and a conventional thermostat?

“A heat pump thermostat is designed to have multiple options for heating your home,” Sherman says. “These are often referred to as ‘two heat, one cool’ thermostats, or similar verbiage.” Because heat pumps almost always have more than one way to heat your home, the thermostat has more wires than a traditional AC or furnace, according to Sherman.

Can I use my existing thermostat wires for a heat pump?

“That depends on whether there are enough wires already in the existing thermostat wire,” Sherman says. “The bare minimum needed to run a heat pump thermostat is five wires.” If your heat pump thermostat wiring has fewer than five wires, “then a new thermostat wire would need to be pulled.”

How do I identify wires if they aren’t labeled?

Before you remove your old thermostat from the wall, take a picture of the connections to determine exactly how the current system is wired. If you forget, or you’re starting from scratch, you can look at the control board on the heat pump or check the instructions for a wiring diagram to verify wire colors match on each end of the system.

About the expert

• Micah Sherman is a virtual HVAC technician for Frontdoor, an app service that connects homeowners with technicians so they can feel empowered to do their own repairs. Sherman is an EPA-licened and certified HVAC technician with 12 years of experience.