2 Speed Thermostat, Adjusts On Low From 60 To 120 Degrees & Adjusts On High From 60 To 120 Degrees, This Product Only Works With 2 Speed Roof Mounted Or Gable Mounted Power Attic Ventilators, Do Not Use With Whole House Fans, Only Works On Model #'s 53837, 53851 & 53861 Which Have Been Discontinued, This Thermostat Should Only Be Used For Replacements Of Defective 2 Speed Thermostats.