Requirements for nanoparticle processing based on energy and cost-effective technologies have increased in recent years. Flame synthesis is widely used on an industrial scale and is superior to gas phase one-step processes for producing nano particles; however, further improvements are required from the viewpoint of energy efficiency. In this work, we present a new aerodynamically stable nanoparticle processing method with extremely low energy losses, based on the use of a tubular flame. The developed tubular flame apparatus is inexpensive and simple to set up, allowing for a uniform and high temperature field with a high energy efficiency. Consequently, highly crystalline and uniform WO3 nanoparticles were successfully synthesized with a high production rate. The simple and energy-effective process proposed in this work has potential for application to various types of functional nanoparticle production.