This paper is concerned with the design and application of a heat engine that deems most appropriate to utilize low grade thermal energy. One of the LTD heat engines tested in the present study has the shape similar to the Gamma-type Stirling engine and the other is based on materials of magneto-caloric effect (such as gadolinium) capable of running on temperature differentials ranging from 90 down to a few degrees Celsius. Especially, the latter was explored as gadolinium generally retains ferromagnetic property at temperatures below 20 °C, but becomes strongly paramagnetic above this temperature. Taking advantage of this magneto-caloric effect, the authors studied different schemes to develop power from low-grade waste heat, which are yet to be completely explored. A series of tests were performed using these heat engines and their results were analyzed to elicit the most effective scheme capable of producing power from low grade heat sources.