Non‐woven carbon fiber sheet‐based heaters have been used for various thermal and material science applications, which possess rapid thermal heating at low input power. This work investigates the optimization of chopped carbon fiber composite sheet for heating applications. Here, different lengths of chopped carbon fiber have been used to fabricate the composite sheet. The parameters of composite sheets, such as morphology, porosity, electrical conductivity, mechanical property, and thermal stability, were studied. Besides, the electrothermal performance of prepared sheet heaters was investigated, and the results were compared at the input voltages of 10 and 12 V. The input power consumed by different sheet heaters was also investigated. The optimal chopped size of the carbon fiber composite sheet showed the highest surface thermal heating temperature of 245°C at 12 V.