As a high-level cybersecurity measure, air-gapped networks are employed in secure environments to physically isolate secure computer networks from unsecured ones, such as the public internet. However, recent studies have shown that these systems are not impervious to breaches. This paper introduces an attack method, Heaker, which targets air-gapped networks by manipulating the thermal emissions of a compromised computer's CPU and GPU. By controlling the workload on these components, the computer's exhaust temperature is modulated with encoded data. An attacker, positioned remotely, can observe these thermal variations using thermal imaging equipment and decode the transmitted information from these temperature fluctuations. We further explore signal encoding methods suitable for the thermal channel and examine factors impacting the attack's efficacy. Our experiments demonstrate the viability of this attack method within a 4-m range and a data transfer rate exceeding 60 bits per hour. This research offers insight into the potential risks of thermal-based side-channel attacks on air-gapped systems and discusses preventive and detection strategies against such threats.