In a heat only boiler system of a steam power plant, outdoor air required for combustion is made to pass through indoor space for increasing the boiler efficiency. Due to heat generated by various equipments, temperature of the air that enters the boiler will increase resulting in combustion efficiency. If the outdoor air temperature is low, however, this will cause freezing and bursting of pipes which are filled with water. It is especially fatal to small diameter pipes and pipes connected to measuring instruments. The purpose of this study is find operation and outdoor conditions where this phenomena can happen and also establish preventive measures to avoid this problem.