Why Do Smoke And Hot Air Go Up A Chimney? Fun Fact For Kids

Joan Agie
Oct 06, 2023 By Joan Agie
Originally Published on Oct 13, 2021
Smoke from the chimney, heating.
Age: 3-18
Read time: 5.9 Min

It's a wonder as to why smoke and hot air go up a chimney.

This is generally a process that can be explained with the help of scientific explanations. There are many scientific reasons why smoke and hot air go up a chimney.

It has been observed that whenever we light a fire in a fireplace, the warm air rises, and also the smoke rises up a chimney. There are two major reasons behind that.

The first reason being, that the fireplace is constructed of flame-resistant materials which trap the air and the second reason specifies that the fireplace forms a chimney draft that causes the stream of heated air at the fireplace to push the smoke up the chimney draft.

When the warm air rises, it leads to the accumulation of more hot gases in a large amount and this makes the smoke continue to rise.

According to some laws of physics, there are three ways that heat moves in the air. They are conduction, convection, and radiation.

Conduction takes place when a hot object comes in touch with another object of a low warm temperature.

Convection happens when hot gas or liquids are transferred into areas with minimum warm temperatures. Radiation takes place when the electromagnetic waves that are generated from the sun or heated lamps transfer for the purpose of making the cooler object slightly warm and again increasing the speed to make them warm at which point their molecules move.

There should be enough air pressure in a room to light the fire and even if we open the windows for this purpose, only the cold air will go out, it will not come in and you can easily light a fire, causing a stack effect on chimneys.

If you find this article helpful, you may also want to check out, why do cells divide and why do your ears pop.

How does hot air go up in a chimney?

The amount of heat that a fire creates comprises a large number of hot gases and when it starts working, it moves in the upward direction or towards the chimney due to the process of convection.

It forms a combination of hot air and the vacuum effect in the room makes sure that the smoke from the fireplace will move in the direction of the chimney without having control of the chimney and this effect can immediately turn the fireplace from getting too hot or filled with smoke.

The task of a draft is that it pulls a large amount of warm air or hot air towards the chimney which results in the reduction of the room temperature.

This helps smoke rise up a chimney and clear the room from smoke. The flow of hot air towards the chimney is also based on the way a chimney is built or constructed.

If it is correctly designed and enables ventilation, the path of the smoke and hot air will naturally travel upwards, and if not, then you should repair it with a chimney pro.

The Science Behind The Working Of A Chimney

Usually, the chimney is constructed in such a way that it fulfills the requirements of keeping the house warm at times, and for that, what is very important is oxygenation. If enough oxygen is not available, then the fire will simply not burn.

So there should be enough draft flow in the chimney to get the fire started. As the gas begins rising through the chimney, it makes a difference in the pressure by clearing the surrounding warm air and smoke.

The next important factor is negative pressure. Chimneys are negative pressure systems.

If you want your electrical heating appliances and the fireplace to work properly, there should be sufficient draft and airflow in the house. For this matter, the chimney draft will help you achieve adjustable airflows in your house and prevent you from having excessive smoke or heat in your place.

A column of heated gas is created inside the chimney of a fireplace. Earlier, some people, such as Benjamin Thompson, also known as Count Rumford, studied and taught the best ways to operate a fireplace, mostly traditional fireplaces, including wood-burning systems.

Some of the laws of physics were also applied for operating the fireplace and the facts on why air goes outside if it could remain within the house were also disclosed. The purpose of a chimney is generally to vent out combustion products from one's home.

Side view of a Galvanized metal chimney.

How does a chimney work?

The very first thing one should keep in mind while constructing a chimney and its wood-burning systems is that it should be constructed with a proper gap outside the upper side of the house.

Chimneys operate on the principle that hot air is less dense than cold air and thus smoke or hot air rises.

A fundamental way to prime a chimney flue is to make a roll, light it and make it towards the damper. As per the laws of physics, when you open a window, the amount of air that is cold will not enter from the window; only the cold air rises and moves out from the window.

This finding has greatly influenced the introduction of chimneys for a fireplace.

If the situation happens where a fireplace and the heating appliances inside the house are below the neutral pressure plane, air will tend to flow into the house through the chimney or vent and colder air will go outside of the house.

There are some basic types of chimneys like factory-built metal, and they have a cap installed in them to prevent water from going around the chimney or leaking outside of the house. Proper wind energy is required when you burn the fireplaces.

When a fireplace is not in use, chilly air from outside can enter the residence through the chimney, and the warm, inside air can escape up the flue.

Reasons Why Smoke And Hot Air Rise Up A Chimney

As stated earlier, there are two basic reasons for smoke and hot air to go up the chimney and they are, the fireplace is constructed of flame-resistant materials and the fireplace forms a chimney draft that causes a stream of heated air at the fireplace, pushing the smoke up the chimney draft.

There should be enough air pressure to build a fire inside the house and in case there is a lack of air pressure, then open the window a bit near the fireplace.

A very basic way to prime a chimney flue is to simply make a roll, light it and make it towards the damper.

When creating a chimney and fireplace, make sure there is a smoke chamber from where the smoke takes an exit out of the chimney through the flue. The fireplace will become smokey and will be collected in the firebox and this is simply a stack effect.

Proper wind energy is needed when you burn the fireplaces, and always ensure to follow appropriate safety measures when doing so.

Here at Kidadl, we have carefully created lots of interesting family-friendly facts for everyone to enjoy! If you liked our suggestions for why do smoke and hot air go up a chimney then why not take a look at why do boats float or why do people dance?

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Written by Joan Agie

Bachelor of Science specializing in Human Anatomy

Joan Agie picture

Joan AgieBachelor of Science specializing in Human Anatomy

With 3+ years of research and content writing experience across several niches, especially on education, technology, and business topics. Joan holds a Bachelor’s degree in Human Anatomy from the Federal University of Technology, Akure, Nigeria, and has worked as a researcher and writer for organizations across Nigeria, the US, the UK, and Germany. Joan enjoys meditation, watching movies, and learning new languages in her free time.

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