Covert communication channels are a significant security threat where the host computer's security policy is bypassed to establish a communication link that can leak sensitive data. Establishing thermal covert channels is feasible because modern processors have accessible temperature sensors that are typically used for dynamic thermal management. In this paper, we first provide an information-theoretic discussion on thermal cover channels and important characteristics such as channel capacity and data modulation methods. Next, we summarize existing thermal covert channel detection methods, including their limitations. We then propose a novel runtime detection method for thermal covert channels where the secret data is encoded via low power programs. Our results demonstrate that the proposed technique can achieve 100% detection accuracy with 0% false positive rate.