The ECO-AIR Gen 3 Interface modules allows you to take your HVAC System combinations to the next level! In Multi-Zone applications you can add any ECO-AIR Indoor Unit to an existing Furnace or Hydronic Air Handler and use the Gen 3-24V Interface to control the Furnace and or AH, with a standard 24V Thermostat. Combine a Mini-Split Multi-Zone System with a conventional Furnace and or AH with ease.