Mysa Baseboard Thermostat Wiring Requirements and Compatibility

Last updated: May 21, 2026

Mysa baseboard thermostats require line voltage wiring to operate properly and need power routed to the thermostat location first to establish a complete circuit. They are not compatible with 2-wire setups.

Wire Requirements

For a successful Mysa baseboard installation, you need:

  • Wire configuration: Mysa models require 4 wires minimum in the wall:

    • For 240V systems: 2 line wires (L1/L2 in) and 2 load wires (L1/L2 out)

    • For 120V systems: 2 wires bringing power (Line and Neutral) and 2 wires going to the heater

    • Minimum gauge size of 12/2 AWG

  • Complete circuit at gang box: Power must be routed to the thermostat location first, not to the heater first. This ensures there is a complete circuit with both power supply and heater connections present at the thermostat location.

  • 240V or 120V system: Most baseboard heaters operate at 240V, though some use 120V. For 120V systems, you need Line and Neutral wires plus two wires to the heater. For 240V systems, you need L1 and L2 wires plus two wires to the heater.

  • 240V circuits have NO neutral wire: Both the black and white wires in a 240V circuit are “hot” wires (indicated by a double‑pole breaker in your panel). The white wire is NOT a neutral in this configuration.

  • Proper amperage rating: Your heater load must not exceed:

    • 3800W on a 240V circuit

    • 1900W on a 120V circuit

    • 3300W on a 208V circuit

    Breaker size: Should be 20 amps

  • Ground wire is not required: Mysa baseboard thermostats do not require a ground connection to operate. If a ground wire is present in your electrical box, coil it up and tuck it into the back of the box.

Important: Check all wires present in your electrical box, not just the wires connected to your current thermostat. Many existing thermostats only use 2 wires even when additional wires are available in the box that would allow Mysa to work. If you have additional wires in your box, you can send photos of the wiring behind your existing thermostat to Mysa support to confirm compatibility. Both Mysa for baseboard V2 and Lite models are typically compatible when extra wires are present.

Standard Wiring Configuration

The typical wiring setup for Mysa baseboard thermostats is:

  1. L2 (Red terminal): Connect to all white wires in the box

  2. L1 (Black terminal): Connect to one group of black wires (usually bundled together)

  3. Load (Black terminal): Connect to the remaining black wire(s) going to the heater

  4. Ground wire: Can be pushed to the back of the box

Troubleshooting Power Issues

If your Mysa doesn't power on after installation:

  1. Turn off power at the breaker

  2. Swap the connections between the L1 and Load terminals

  3. Turn power back on

  4. Look for a smiley face on the display to confirm correct wiring

Incompatible Setups

Mysa baseboard thermostats will not work with:

  • 2-wire systems: These typically control relays or contactors and don't provide the necessary power configuration

  • Low-voltage systems: These require a different Mysa model (Central HVAC/Smart Thermostat)

  • Proprietary systems: Some manufacturers use specialized thermostats that cannot be replaced

When You Only Have 2 Wires

If you only have a 2‑wire cable in your electrical box (one cable with 2 wires plus ground), you have a few options:

  • Consult an electrician: They can assess whether additional wiring can be run

  • Consider Mysa for Central HVAC: If your system uses relays, this model with a C-wire adapter might work

  • Alternative thermostats: Look for line voltage thermostats specifically rated for your heater's amperage

Always turn off power at the breaker before working with electrical wiring, and consult a qualified electrician if you're unsure about your system's compatibility or safety.