Taco VR1816 Viridian Infinitely Variable Speed, ECM High Efficiency Circulator Pump (110-120V) High-efficiency ECM motor uses up to 85% less electricity | Highest pump efficiency in its class | Infinitely variable speed settings to fine tune flow for any system LED displays operating mode and error code diagnostics | Easy to use dial to set operating modes | 18' Shut-off head, 16 gpm max flow ECM High-Efficiency Motor | Operates in 3 different modes: Infinitely Variable Fixed Speed, Constant Pressure (Self-adjusting, Variable Speed) & Proportional Pressure (Self-adjusting, Variable Speed) | LED displays: Operating mode or error code diagnostics Easy to use dial to set operating speed or pressure control | Use with a Taco ZVC Zone Valve Control or SR Switching Relay for ON/OFF operation | Integral Flow Check (IFC) included Dual electrical knockouts | Whisper quiet operation