The ZR 011 houses two separate thermostats, allowing the independent control of heating and cooling or other equipment. Thermostat NC (normally closed): Thermostat opens at temperature rise – for regulating heaters or for switching signal devices. Comes with red temperature dial. Thermostat NO (normally open): Thermostat closes at temperature rise – for regulating filter fans and heat exchangers or for switching signal devices. Comes with blue temperature dial.