How Does a Hot Air Balloon Work?

How does a hot air balloon work

The hot air balloon is one of the most intriguing flying inventions made by humankind. It was invented and introduced to the public by the French brothers Joseph-Michel and Jacques-Étienne Montgolfier in 1783.

Today, these balloons are often used in scientific investigations by the National Aeronautics and Space Administration (NASA). One of the hot air balloon's most recent tests was in June 2021 where the mission was to see if certain technologies could overcome the challenges that come with high altitudes.

Others simply ride in a hot air balloon for leisure purposes with many riders say that the experience is one of the most calming activities they have done.

How Does a Hot Air Balloon Work?

Hot air balloons work simply because warmer air rises in cooler air.

Because hot air balloons don't have engines, they need to be lighter than air to fly.

We tend to think of air as being "weightless", but the molecules oxygen and nitrogen in the air do in fact have weight. A cubic foot of air weights approximately one ounce.

If you heat the air inside a balloon, the molecules start to move faster and spread further apart. This causes the balloon to become lighter than the air outside of it.

Each cubic foot of hot air is roughly 7 grams lighter than cold air. So, to lift 1,000 pounds, a hot air balloon needs to be about 65,000 cubic feet.

To keep the molecules consistently far apart, propane burners keep the air hot as a balloon rises.

When you want to go up, you provide more heat. And when you want to go down, you open a hatch on the side of the balloon that releases hot air.

Since you can only steer the balloon using ever-changing wind patterns, you can't determine where you are going to land exactly. This is why most pilots have co-pilots on the ground to follow them.

Main Parts of a Hot Air Balloon

To understand better how a hot air balloon works, t’s important to learn about the primary parts of a hot air balloon first.

The following are the main parts of a hot air balloon that make it work:

  • Envelope: The envelope is the balloon. Besides giving the craft its well-known design, this structure plays an essential role in allowing it to take flight and maintain altitude. The material used in creating the envelope is carefully engineered to allow it to glide above the ground resistant to tears, and it contains an opening that lets its operator control its ascent and descent. (Browse hot air balloon envelopes)
  • Basket: The basket is the part that carries the operator and the passengers up in the sky. It is made using durable yet lightweight material and can hold as few as two individuals or more. This part also has extremely durable load-bearing ropes attached to the envelope that connect the two. (Browse hot air balloon baskets)
  • Burner: The burner is the mechanical aspect of the hot air balloon. It consists of propane cylinders that are designed to generate hot air that allows the balloon to rise in the air. Each of these cylinders is capable of holding 70 to 90 liters of fuel and can weigh as much as 60 kilograms. This part of the craft the operator controls to let it go up or down.

How to Ascend or Descend a Hot Air Balloon

How do pilots control how the hot air balloon rising and descending?

The operator of the balloon can cause it to rise by using the burner that is positioned at the opening of its envelope. Activating the cylinders will cause the air in the balloon to heat up, and thus, rise.

The Montgolfiers brothers used straw and wool as fuel to heat a hot air balloon, while the ones we use today consume propane. The fuel is stored in liquid form and is kept as lightweight and compressed as possible to minimize its load. The dense form of the propane allows it to flow quickly and reach the heating coil.

The fuel flows out and is ignited using a device known as the pilot light when the balloon operator activates the burner. As the liquid propane goes through the process, it changes its form from liquid to gas, causing a more powerful flame upon being ignited.

It’s the job of the operator to control how high up the balloon should go and allow it to descend safely once the journey is about to end. Increasing the flame’s intensity causes the balloon to rise, while lowering it results in it going down.

Since buoyancy is in play, the heated air inside the envelope will stay inside and not escape. The operator only has a limit to the highest altitude they can reach with the balloon. At a certain height, the air will become especially thin, which will cause the balloon to stop rising no matter how much it is heated. For more information, read our post: How High Can a Hot Air Balloon Go?

How to Pilot a Hot Air Balloon

Steering a hot air balloon is fairly straightforward, but it requires skill to maneuver it properly.

Interested in becoming a pilot? Check out our guide and learn how to get a hot air balloon license.

The ability to go up and down is the only direct means for the operator to control the hot air balloon. To get the craft to go in a different direction horizontally, they need to change its vertical positioning and take advantage of the way the wind blows.

The operator does this by rising up and going down at the right altitudes, riding the wind as they do so. Changing the altitude is the primary technique that an operator would take advantage of since wind is stronger higher in the atmosphere.

How to Land a Hot Air Balloon

Landing a hot air balloon is a different matter altogether. They aren’t the same as regular aircraft that are capable of landing in designated locations.

This is because a hot air balloon cannot be steered as precisely as the operator would want. For standard flights, operators would land their balloons after an hour in the air upon spotting a safe area to do so.

All of the passengers are advised to crouch by bending their knees and holding on to the ropes provided in the basket. They should then have their backs in the direction where the balloon is traveling for added safety.

Upon nearing the ground, the operator vents the heated air at the top of the envelope, causing it to escape, resulting in the hot air balloon descending further.

Touching down usually results in a slight bump or skid, so all hot air balloon passengers should expect this. There’s also the possibility of the basket appearing to tip over, but that’s normal.

What Gas Is Used in Hot Air Balloons

Most hot air balloons are powered by a jet of flame produced by burning liquid propane in a propane burner. The hot air generated by the burning fuel powers the balloon by expanding and rising within the balloon's envelope to lift it into the air. The typical hot air balloon carries enough fuel for about 60-90 flight times.

The burner is placed inside the envelope and consists of one or more gas cylinders connected to a manifold. The gas cylinders are usually made from aluminum or stainless steel and contain about 30-40 pounds of propane. The manifold regulates the flow of propane to the burners.

Do Hot Air Balloons Use Helium?

Helium is not the most common gas to fill a hot air balloon. Rather, it is usually filled with air.

There are several reasons for this. First, helium is a very scarce resource.It's much more expensive than air, so it would be quite costly to fill a hot air balloon.

Secondly, helium is a very light gas. This means that it would quickly escape from the balloon, making it difficult to keep the balloon inflated for very long.

Finally, helium is non-flammable, so using it in a hot air balloon would pose a safety risk.

Hydrogen is another gas that is sometimes used to fill hot air balloons, but it's even more expensive than helium and poses an even greater safety risk.

How Much Fuel Does a Hot Air Balloon Use?

It all depends on the size of the balloon. A small hot-air balloon might use about 20 gallons of propane per hour, while a large one could use up to 60 gallons. Most hot air balloons have two burners, so they use twice as much propane when both burners are going.

Hot Air Balloons: Convection, Radiation, or Conduction?

The answer to this question depends on how you define these terms. Strictly speaking, convection is heat transfer by moving fluids, while radiation is heat transfer by electromagnetic waves. However, in many cases, these terms are used more loosely, and hot air balloons can be said to use both convection and radiation to heat the air inside the balloon.

Hot air balloons work by heating the air inside the balloon using a burner. The hot air inside the balloon expands, causing the balloon to rise. Convection plays a role in this process, as the hot air rises and cooler air rushes in to take its place. However, radiation also plays a role, as the hot air inside the balloon emits infrared waves that heat the surrounding air.

As a result, both convection and radiation play a part in making hot air balloons work.

Are Hot Air Balloons Bad for the Environment?

Hot air balloons are powered by burning fossil fuels. And while the balloons are lightweight nylon or polyester fabric, the inflation gasses (usually nitrogen or helium) are often stored in metal cylinders. It's no surprise that some people view hot air ballooning as environmentally unfriendly. But is it? Are hot air balloons bad for the environment?

The answer may depend on how you look at it. On the one hand, hot air ballooning requires burning fossil fuels and using materials that are not biodegradable. On the other hand, the environmental impact of hot air ballooning is quite small compared to other forms of recreation and transportation.

In fact, according to some estimates, a single hot air balloon flight has approximately the same carbon footprint as a 60-mile car trip. And when you consider that you can enjoy hot air ballooning without harming any wildlife or natural habitats (unlike activities such as skiing or mountain biking), you could argue that hot air ballooning is one of the most environmentally friendly forms of recreation available. 

Does a Hot Air Balloon Have an Engine?

No, a hot air balloon does not use an engine. Hot air balloons rely on a simple principle to stay afloat: warmer air rises.

The balloon is heated by the burner, causing it to inflate. As the air inside the balloon cools, it descends. This means that a hot air balloon does not need an engine to fly.

How Hot Is the Air in a Hot Air Balloon?

Generally, the air inside a hot balloon can reach temperatures between 100 and 200 degrees Fahrenheit.

However, the air inside can get even hotter if the balloon is large enough and the conditions are right. On rare occasions, temperatures inside a hot air balloon have reached more than 1,000 degrees Fahrenheit.

It's important to note that passengers inside the balloon are not exposed to these extreme temperatures; the heat is contained within the balloon's envelope. However, it is still important to dress appropriately for a hot air balloon ride, as you may be exposed to warmer temperatures than you are used to.

How Fast Do Hot Air Balloons Go?

While most people think of hot air balloons as leisurely aircraft, they can reach speeds of up to 80 miles per hour. Hot air balloons have even been used in races. The world record for the fastest hot air balloon flight is held by a team from the United Kingdom, who achieved a speed of 126 miles per hour in 1999.

In average conditions, however, hot air balloons typically travel around 10-15 miles per hour.

Of course, a hot air balloon's speed largely depends on the wind. If there is no wind, the balloon will not be able to move.

So, while a hot air balloon can go quite fast in the right conditions, it is ultimately at the mercy of the wind. But even in calm conditions, a hot air balloon can still travel at a respectable speed.


Modern hot air balloons consume propane as their primary source of fuel. It is activated through a burner which causes heated air to be released into the envelope, causing these balloons to rise.

Piloting a hot air balloon appears to be quite direct since the only actions that are in direct control of the operator are its ascent and descent. Fortunately, wind speed increases at higher altitudes, allowing hot air balloon pilots to time these changes to steer their crafts.

Landing is also quite difficult to perform in a hot air balloon, but skilled operators can do this easily through a series of techniques.