Product Description Taco Variable Speed Delta-T Circulator's all-in-one design combines a microprocessor based variable speed differential controller with the reliability and convenience of the 00 Cartridge Circulators. Simply dial in the design Delta-T of the system or zone (from 5 - 50 Degree) and then sit back and watch the circulator automatically adjust its performance to match the systems ideal BTU/hr. output, while conserving energy and eliminating velocity noise. From the Manufacturer Taco Variable Speed Delta-T Circulator's all-in-one design combines a microprocessor based variable speed differential controller with the reliability and convenience of the 00 Cartridge Circulators. Simply dial in the design Delta-T of the system or zone (from 5 - 50 DegreeF) and then sit back and watch the circulator automatically adjust its performance to match the systems ideal BTU/hr output, while conserving energy and eliminating velocity noise.