Wiring Requirements — Mysa for In-Floor Heating

What the electrical box needs to have before you buy. Mysa for In-Floor Heating is a line-voltage thermostat — it connects to single-phase 120V, 208V, or 240V wiring.

What is required

• A dedicated circuit for the in-floor heating system

• Copper wire only. Do not use this thermostat with aluminum wire

• A line cable (power from the breaker) and a load cable (out to the heater), kept separate at the terminals

• A ground wire (green or bare copper)

• A floor sensor connected to the sensor terminals — the thermostat will not operate without one

120V vs 240V

• 120V — a neutral wire must be available in the box. Mysa N connects to that neutral.

• 240V — there is no neutral. Both wires from the breaker are hot, and Mysa N connects to the second hot leg (L2).

A single-pole breaker indicates 120V. A double-pole breaker indicates 208V or 240V.

Do not use an existing GFCI circuit

Mysa has a built-in Class A GFCI that cannot be disabled. Installing it on a circuit that is already GFCI-protected causes nuisance trips and prevents the heater from running. See GFCI Requirements — Mysa for In-Floor Heating.

Box size and full system requirements are listed in the In-Floor Heating Compatibility Guide. For terminal-by-terminal instructions, see the Wiring Guide after purchase.