This kind of heater adopts three pass circular tube design for sufficient heating surface, and the waste heat boiler and energy-saving device disposed at the tail of the heater can greatly reduce the loss of thermal energy, the thermal efficiency can be as high as 95% or more. Advanced low NOx burner can achieve NOx emissions below 30mg/Nm³. And the operation of the thermal oil heater can realize full automatic control, and can automatically adjust the combustion, high tank level, outlet temperature and flow to ensure the safe operation. This series of thermal oil heaters are favored by all walks of life in the chemical, rubber and food industries.