Why Do Hot Air And Smoke Go Up A Chimney? (Find Out Now!)

Heather Robbins
by Heather Robbins

As we all grow up, we have all been able to make the same observation about hot air and smoke: They rise. So when you light a fire in a fireplace or elsewhere, the hot air and smoke both rises. Although this phenomenon seems to be common knowledge, have any of us ever stopped to consider why this happens? How does the majority of the hot air and all of the smoke know to go up the chimney? We have the answer for you!

Smoke and hot air go up a chimney because of two primary reasons: One is that the fireplace is created from flame-resistant materials. The second reason is that the fireplace creates a draft that causes a stream of heated air in the fireplace, pushing the smoke up the chimney. Therefore, when the hot air rises, it draws more of the hot gases under it so that the smoke and hot air continue to rise.

In this article, we will dive deeper into the mechanics of a traditional fireplace. We will also provide you with some basic instructions on how to operate your fireplace the correct way to ensure your smoke is evacuating in the manner it should. As a bonus, we’ve included some vocabulary terms you should be familiar with so that you can better understand the operations of your fireplace.

The Mechanics Behind Traditional Fireplaces

When you light a fire in your living room, there are two main challenges. You have to ensure that the flames are contained within the fireplace so that there is no danger of setting the house on fire. Also, you need to prevent smoke from filling the room. Your fireplace is designed to avoid both of these eventualities.

First of all, your fireplace is constructed using flame-resistant materials, typically stone or brick, but sometimes metal or tiles. It also ensures smoke is evacuated efficiently by directing it up the chimney.

How Your Fireplace Creates A Draft

From a mechanical point of view, the essential job that your fireplace does is creates a draft. We all know that hot air rises: Just think of how a hot air balloon stays in the air. The fireplace creates a stream of heated air inside the chimney. As it rises, more hot gases are drawn up after it. As they rise up the chimney, a draft is created.

The draft has another essential function. All fires need a constant supply of oxygen to keep burning. As the hot air rises, it drags more fresh air, and therefore oxygen, onto the burning fuel.

The Three Ways That Heat Moves

According to the laws of physics, there are three methods by which heat moves:

  • Conduction: When a hot object comes into contact with an object with a lower temperature
  • Convection: When a movable substance, for example, hot gas or liquids, transfer into areas at a lower temperature
  • Radiation: When electromagnetic waves, for example, from the sun or a heated lamp, transfer heat to cooler objects, warming them by increasing the speed at which their molecules move.

Typical fireplaces heat via radiation: Flames and burning wood or coals emit rays that reach people or things in the room, increasing the speed at which molecules move and generating heat. However, convection is also a factor in fireplaces, which is part of why they are not always very efficient in heating a room.

How Does The Heat Move Within A Fireplace?

Most of the heat that a fire creates is comprised of hot gas. When this moves up the chimney due to convection, it doesn’t heat the room but is wasted. Not only that, but the draft also pulls more warm air from the room up the chimney, which results in a reduction of the room temperature. In fact, certain experts claim that a traditional fire draws four to ten times as much air from the room as the fire actually needs to burn.

It can happen that the room loses more heat due to convection than it gains through radiation. This can result in negative energy efficiency. The lower the temperature outside, the colder the air that the fireplace draws in, and the lower the efficiency will be overall.

Basic Tips On Operating A Traditional Fireplace

To get the fire going, you’ll need to start with some kindling. These are small pieces of wood that will catch fire easily. Pile a few logs into the grate and position kindling below and around them. Ensure the damper is open, then light the kindling with newspaper or a fire starting log.

Important Note: Never use a lot of paper, as burning pieces can travel up the chimney and onto the roof, creating a fire risk. For obvious safety reasons, never use gasoline, lighter fuel, or a blow-lamp to light your fire.

What If Smoke Isn’t Going Up the Chimney?

Even when the fire is burning, some might sometimes flow back down into the room. One reason this occurs may be that the house is too tightly sealed. Without enough ways that air can enter the room to replace that which is being pulled up the chimney, therefore creating negative pressure,f from which a partial vacuum develops.

This vacuum pulls air back down into the room to restore the air pressure, and the result can be a room filled with smoke. The simple solution is to open a window slightly to allow more air to enter.

Best Types Of Wood For Your Fireplace

Using a typical wood-burning fireplace is relatively easy, providing a few simple guidelines are followed. The first requirement is the right fuel to burn. Choose hardwoods, including:

  • Hickory
  • Ash
  • Oak
  • Hard maple

Softwoods like pine and spruce typically don’t burn as easily or give off the same amount of heat. So, it’s a good idea to steer clear of softwoods unless you’re using them solely to build a fire.

In addition, be sure that the wood is seasoned or dried-out. It will take between 6 months and a year for the wood to dry to the recommended level of 20% moisture. This is the maximum required you create a well-burning fire.

How Do You Tell If Wood Is Seasoned?

To assess whether the wood is correctly seasoned, knock two pieces against each other. They should sound hollow, not make a dull thud. Seasoned lumber tends to be darker in color, and you’ll see cracks and fissures in the grain at the end of the piece.

Don’t use wet or rotten pieces of wood. Chipboard and pressure-treated wood shouldn’t be burned as firewood. Also, never use your fireplace to burn trash or cardboard.

The Parts Of A Traditional Fireplace

Parts of a Fireplace




HearthA structure that stretches above the fireplaceMade of fireproof materials to keep the fire inside the fireplace
SurroundThe area that surrounds the fireplaceFireproof materials create an area where the fire can be contained.
FireboxThe inside of the fireplaceHolds the fire and the smoke
FlueThe channel at the top of the firebox.Made from baked clay or stainless steelSmoke and gases pass through this to exit the chimney.
ChimneyThe area that surrounds the fluePrevents heat from coming into contact with any flammable materials nearby
Smoke ChamberAn area which connects the fireplace with the flueThe smoke chamber is where the smoke can build to exit out of the chimney through the flue.
DamperAn adjustable cover that separates the firebox from the space above itIt limits any cold air coming down into the house when there isn’t a fire burning.Not all chimneys have a damper
Spark ArrestorMetal mesh material that sits on top of the flueEnsures that escaping gases cannot carry burning objects onto the roof.
Chimney CapA product to protect the entrance of your chimneyPrevents water and wildlife from entering and nesting in the flue of your chimney.Some models prevent wind gusts.
Ash DumpAn opening for ashes to sitYou can push the ashes into this spot to empty later on.
DoorsDoors that allow you to shut the fireplaceYou can shut off airflow by closing the doors, which will eventually cause the fire to burn out.

Wrapping It Up

Fireplaces are virtually self-sustaining mechanisms as far as the flow of smoke, and hot air goes. Minimal amounts of maintenance need to be done to encourage them to go to their rightful place: Up the chimney. However, sometimes you will notice that smoke is pouring out into your living room. If this happens, you simply need to crack a window or a door, and the problem will solve itself.

Learning the different elements of a fireplace and how they work together will help you better understand exactly how your fireplace functions. This knowledge aids you in understanding all there is to know about operating a fireplace safely. And yes, it even helps you understand exactly why hot air and smoke go up the chimney. Every always says that knowledge is power; however, knowledge can also aid in safety.

Heather Robbins
Heather Robbins

Heather is a passionate writer who loves anything DIY. Growing up, she learned everything from home repairs to design, and wants to share her tips with you. When she's not writing, she's usually hiking or searching for her next DIY project.

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