What is the name of the top opening that lets a hot-air balloon pilot release heated air?

A parachute valve is the top opening that lets a hot-air balloon pilot release heated air.

The valve is fitted into the crown, or top, of the envelope. The pilot operates it with a control line from the basket. Pulling the line opens the valve so hot air can escape, reducing lift and helping the balloon descend. Releasing the line allows the valve to close again.

The name can be confusing because the device is not a parachute used to carry the balloon. It is a circular fabric valve that resembles a parachute canopy and is sometimes called a top vent. Some balloons also have separate deflation systems used to empty the envelope completely after landing.

Pilots control altitude by balancing heat input and air release. The burner adds heat and increases lift, while the parachute valve vents hot air. Horizontal movement is different: ordinary hot-air balloons generally drift with the wind rather than steering like airplanes.