Proportional Temperature Controller, 24-30Vac, 0-100 Degree Setpoint Temperature Range, 125 Degree Maximum Operating Temperature, 3-30 Degree Throttling Range, 1/2"x4 3/16" Copper Bulb Size, 5' Capillary Length, One 135 Ohm Potentiometer Analog Output, Provides Modulating Control of Water or Air Temperature in Ducts or Tanks