How did the Newcomen steam engine waste steam and fuel?

The Newcomen steam engine was inefficient because it relied on a single-cylinder design that required the cylinder to be repeatedly heated and cooled with every stroke.123

In the Newcomen engine, steam was condensed directly within the cylinder to create a vacuum, which allowed atmospheric pressure to push the piston down. This process meant that the cylinder had to be cooled to condense the steam and then reheated to accept the next charge of steam. This cycle resulted in a significant loss of latent heat, which James Watt identified as the engine's primary defect. Because so much energy was wasted in the constant heating and cooling of the cylinder, the engine consumed excessive amounts of fuel.45231

Watt solved this problem by inventing a separate condenser, which allowed the cylinder to remain hot while the steam was condensed in a distinct, connected chamber. This innovation drastically reduced steam waste and improved the overall fuel efficiency of the engine.162