Sealing performance and heat loss are important factors for PFJs subjected to medium or high temperatures. The heat insulation layer may not be applied considering the sealing performance of PFJs. However, the heat loss is of great interest in practical engineering for naked PFJs. Therefore, the heat loss of PFJs was tested and simulated considering various ambient temperatures of -10°C, 0°C, 10°C, 20°C, 30°C and 40°C, wind speeds of 0m/s and 3m/s and target temperatures of 200°C, 300°C and 400°C. It is worth noting that the experiments were performed during summer for high ambient temperature and during winter for low ambient temperature. Results present that the steady temperature slightly increases with the increase of external ambient temperature. However, the wind speed decreases significantly the steady temperature under the same condition, especially when the higher target temperature is applied. The heat loss approximately goes up to 30.8%, 22% and 25% when the ambient temperatures are 30°C, 20°C and 10°C under the windless condition, respectively. However, if the external wind speed is 3m/s, the heat loss enhances almost 38.4%, 30.7% and 23.6% correspondingly. Moreover, the simulated temperatures agree well with the tested temperatures in most cases, and the average error is almost 7.55%. The energy saving efficiency under the windless condition is almost on average 25.97% higher than that subjected to the wind speed of 3m/s.