WarmlyYours - Thermostat Master 12VDC - A Master Thermostat with a Dual Voltage Power Module is required for all floor heating system installations utilizing more than 240 square feet of floor heating product when operating on a 240 volt circuit. Use also when operating a floor heating system on a 120 volt circuit with more than 120 square feet of floor heating product. Each Master Thermostat requires a minimum of one Dual Voltage Power Module. Each additional Power Module provides an additional 15AMPS of service and up to 10 Power Modules can be added to each Master Thermostat.