Tekmar tn4 Thermostat Communicating Touchscreen. tekmarNet??rmostat 557 is a communicating touchscreen rmostat designed to operate eir: a hydronic radiant floor with a two stage heat pump (water-to-air or air-to-air) for heating & cooling and an emergency backup heating system; or two stages of heating and two stages of cooling. re are three auxiliary sensor inputs that can be used to measure room, floor, outdoor or duct temperature. optional floor sensor allows precise heating of radiant floors. Relative humidity level can be measured and controlled using eir built-in or external humidity sensor. large touchscreen display allows you to easily adjust 7-day programmable schedules and room temperatures to optimize comfort and energy savings. 557 can connect to tekmarNet??controls using two or four wires or it can operate as a stand-alone device.