Fluctuating heat radiating from the environment is an unused and unknown source. This study investigates pyroelectric energy harvesting as a way to tap a fluctuating radiation heat source. Appropriate circuitry coupling and the frequency of the radiation source play a key role in the ability to harvest this energy. Hence, a design of experiment approach that limits factors to temperature change frequency, electrical resistance, and capacitance is utilized to develop a full-factorial model at three levels for each factor. In order to quantify and maximize the harvested energy, a response surface model was developed. The optimum values for temperature change frequency, resistance, and capacitance were predicted to be 0.05 Hz, 7330 k, and 100 µF, respectively, for a PZT-5A sample with a volume of 0.684 cm³. The maximum response of 62.89 µJ was predicted for the optimum values.