Korean Ondol: 2,000 Years of Traditional Floor Heating
This summer in Korea was brutally hot.
"Hot" almost doesn't seem strong enough.
On August 2, 2026, the temperature in Yangsan, South Gyeongsang
Province, soared to 42.5°C (108.5°F). It was the highest temperature
recorded in Korea since modern weather observations began in 1904.
The summer I experienced here in Korea was beyond anything I had
imagined.
Stepping outside in the middle of the day without a sun umbrella could
leave me feeling dizzy and physically overwhelmed.
And it wasn't just for a day or two.
Did it cool down after sunset?
Not really.
The heat lingered well into the night.
There were days when I honestly wondered how we would have made it
through such a long summer without air conditioning.
But even that scorching summer is finally beginning to fade.
And recently, another thought crossed my mind.
"How cold will this winter be?"
Korea shows a completely different face in winter.
When icy winds sweep through and temperatures plunge, people will wear
almost anything that helps keep them warm.
Thick padded coats, insulated pants, scarves, gloves---we bundle
ourselves up from head to toe.
And then something rather funny happens.
Outside, people are wrapped in heavy winter coats, their breath turning
white in the freezing air.
But the moment they get home, off come the coats.
Before long, some people are walking around indoors in T-shirts and
shorts. And yes, even in the middle of winter, plenty of Koreans still
drink iced Americanos filled with ice.
Outside, bitter winter winds are blowing.
Inside, it feels like a completely different world.
What makes that possible?
The answer is something so familiar to Koreans that we rarely stop to
think about it:
A wonderfully warm floor.
That warmth comes from ondol, Korea's traditional system of floor
heating.
1. If the Fire Was in the Kitchen, How Did the Floor Get Warm?
To understand traditional ondol, we first need to know a few Korean
words: agungi, gudeul, and gudeuljang.
An agungi was the traditional firebox in a Korean kitchen, where
wood or straw was burned.
It was usually located beneath a large iron cauldron, and fuel was fed
through the opening below.
But that fire was not used only for cooking.
The fire in the agungi was also the starting point of the home's heating
system.
In traditional ondol, hot air and smoke from the fire traveled through
channels beneath the floor, heating the large flat stones above.
So what was gudeul?
Simply put, gudeul was the underfloor structure that made traditional
ondol heating possible.
When a fire was lit in the agungi, hot air and smoke traveled through
passages beneath the room.
Large, flat stones called gudeuljang were laid over those passages.
As the hot air passed beneath them, the stones absorbed the heat. The
warmth stored in those stones then radiated upward through the floor and
into the room.
Finally, the smoke escaped through a chimney.
▲ Traditional ondol structure --- agungi → underfloor heat channels →
gudeul stones → chimney
Source: Dzihi / Wikimedia Commons / CC BY 3.0
Once you understand this structure, old Korean expressions such as
"laying the gudeul" or "repairing the gudeul" suddenly make sense.
There were no thermostats on the wall.
There was no button to press to turn on the heat.
Heating the house began with lighting a fire in the agungi.
Looking back, I sometimes think my grandmother, mother, grandfather,
aunt, and uncle were all first-rate heating engineers.
They knew how much straw or wood to add and how to control the strength
of the fire.
And if a room wasn't heating properly, they could even open up the
floor, find the problem, and repair the gudeul themselves.
But where did they learn all of that?
My father probably learned by watching my grandfather lay and repair
gudeul stones.
My grandfather would have learned by watching his father, and his father
would have learned from the generation before him.
That knowledge was passed from one generation to the next---not through
instruction manuals, but by watching, helping, and doing.
Generation after generation.
That is how the wisdom of ondol lived alongside Korean families for
centuries.
When I think about it now, it really is remarkable.
And the fire in the agungi did not warm only the room.
It cooked rice in the cauldron, heated water, and warmed the floor.
Our ancestors found several uses for a single fire.
2. Just How Old Is Ondol?
When you begin looking into the history of ondol, you discover that it
goes back much further than you might expect.
According to information on Korea's ondol culture published by
Korea.net, archaeological remains related to ondol have been found in
several areas of the Korean Peninsula dating back hundreds of years
before the Common Era. The source describes ondol as having a history of
more than 2,000 years.
A 2008 academic study published by the Korea Institute of Ecological
Architecture and Environment also examines historical records showing
that ondol was widely used in Goguryeo and continued to be used through
the periods of Silla and Baekje, and later during the Goryeo and Joseon
dynasties.
So beneath the warm floors that people in modern Korean apartments take
for granted lies a history stretching back well over two thousand years.
Academic Research on the History and Characteristics of Traditional
Korean Ondol ---
KCI
3. Ondol Changed the Way Koreans Lived
Ondol did much more than simply keep a room warm.
Once the floor itself became warm, the floor naturally became the center
of everyday life.
People removed their shoes before entering the room and sat directly on
the warm floor.
Families placed a low dining table on the floor to eat together.
They sat there talking.
And at night, they spread out their bedding and slept on the floor.
Research on Korean housing culture also explains that warm, clean ondol
floors helped shape the Korean custom of removing shoes indoors and
living close to the floor.
There is another word that is deeply familiar to older generations of
Koreans:
Araetmok.
The araetmok was the warmest part of a traditional ondol room,
usually the area closest to the heat coming from the agungi.
When winter arrived, people naturally gathered there.
For me, araetmok is not an old Korean word I learned from a book.
It was a real place.
It was part of the home where I spent my childhood.
4. The Korean Winters I Remember
Korean winters felt terribly cold and very long when I was a child.
We wore jackets and pants thickly padded with cotton, along with hats
and gloves, but even all of that could not completely keep out the
bitter winter cold.
Children are funny, though.
No matter how cold it was, once we met our friends in the neighborhood,
we seemed to forget about the weather.
We played marbles.
We played biseokchigi, a traditional game of knocking over stones.
We played rubber-band games and jegichagi, a Korean kicking game
somewhat similar to keeping a shuttlecock in the air.
If there was a game to play, we played it.
After hours outside, I would finally come home with my hands and feet
practically frozen.
And something wonderful would be waiting for me.
The warm araetmok.
I would come inside from the freezing cold and slide my feet underneath
the bedding spread over the warmest part of the ondol floor.
At first, it felt almost too hot.
But before long, my frozen body would slowly begin to thaw, starting
from the tips of my toes.
I would crawl completely underneath the bedding, leaving only my nose
sticking out, and simply enjoy the warmth.
Of course, my siblings had usually gotten there first and were already
warming their own frozen feet under the blankets.
And that was when the mischief began. Haha.
We couldn't even tell whose feet were whose under all that bedding.
We would push and pull at one another with our feet, laughing and
fooling around until the blankets turned into complete chaos.
Even now, remembering that scene makes me smile.
Ah, how I miss those days...
After all that playing around, my mother would come into the room
carrying our dinner table.
She would set the low table on the warm araetmok, and the whole family
would sit around it together and enjoy dinner.
Looking back now, that dinner table was about much more than simply
eating a meal.
It was the time when family members who had spent the day out in the
cold gathered together in the warmest place in the house.
I also remember those winter nights very clearly.
As the night grew deeper, fierce winds would blow in and shake the
sleeping bamboo grove.
Buckets, washbasins, and dippers left in the yard would roll around in
the wind, and even the latch on the front gate seemed to cry out in the
cold.
Crash, bang, clatter, creak.
There were many nights when those sounds continued for hours and kept me
from sleeping.
When morning came, a fire would once again be lit in the agungi beneath
the large iron cauldron.
That one fire warmed the gudeul stones, cooked our breakfast, and heated
water.
We used that warm water to wash our faces and hair, and sometimes to
bathe.
But even after washing with warm water, the moment we stepped outside,
our hands and faces quickly turned cold again.
On especially bitter mornings, we had to be careful if our hands were
still wet when touching a metal door handle that had been exposed to the
freezing temperatures all night.
I remember times when a wet hand touched the icy metal and actually
froze to it.
When that happened, my grandmother would bring a warm, wet cloth and
gently warm the place where my hand had frozen to the handle.
Only then could my hand finally come free.
That was how cold Korean winters could be.
But after opening that door and coming back inside, where do you think I
went?
I would quickly shut the door behind me and hurry straight back to the
warm araetmok, practically rolling myself into the bedding.
Modern heating is wonderful.
It is comfortable, convenient, and warm.
And yet, for some reason, I still miss the particular warmth of the
araetmok in our old hanok---and even the familiar smell of that room.
Ah, I really do miss those days.
That is how I remember the winters of my childhood:
the fierce cold outside,
and the warm araetmok waiting inside.
Perhaps that is why, for Koreans, ondol was never simply a heating
system.
It was where we warmed our bodies after coming in from the cold.
It was where the family sat around one table and shared a delicious
meal.
And it was where we laid down our tired bodies at the end of the day.
Ondol was a technology for heating a home.
But it was also a warm floor that brought a family together.
5. The Agungi Disappeared, but Ondol Did Not
As time passed, heating systems in Korean homes changed.
Academic research generally describes the development of Korean
residential heating in three broad stages.
Before the 1950s, traditional ondol was commonly heated with wood or
straw.
From the 1950s through the late 1970s, coal briquettes became widely
used.
Beginning in the late 1970s, modern floor-heating systems using hot
water circulating through pipes beneath the floor became increasingly
common.
In the old days, heat from a fire in the agungi warmed the gudeul
stones.
In a modern Korean apartment, a boiler heats water, and that hot water
circulates through pipes beneath the floor.
The technology is completely different.
But one basic idea has remained unchanged:
Warm the floor.
Agungi fireboxes have largely disappeared from modern homes, and few
people today ever see traditional gudeul stones.
But when winter comes, Koreans still want warm floors.
Perhaps it is better to say that ondol never disappeared.
It simply changed its form to fit a new age.
And when I think about it, it makes me smile.
In the old days, my grandmother, mother, grandfather, aunt, and uncle
were our family's expert heating engineers.
Today, a little thermostat on the wall does most of the work for us.
^^
Research on the Historical Changes in Korean Residential Heating ---
Energy and
Buildings
6. And Then a World-Famous Architect Enters the Ondol Story
Follow the story of ondol far enough, and an unexpected name appears.
The American architect Frank Lloyd Wright.
According to a 2005 study published by the Architectural Institute of
Korea, Wright encountered Korean traditional ondol while in Japan and
later incorporated the concept of floor heating into his own
architecture.
He did not simply copy traditional ondol.
Instead of sending hot smoke beneath the floor as traditional ondol did,
he used systems in which steam or hot water traveled through pipes to
warm the floor.
Researchers have described Wright as an important figure in introducing
the idea of this kind of floor heating to the United States.
The warm floor that Koreans had lived with for generations---something
so ordinary that we hardly thought of it as remarkable---appeared to a
world-famous architect as an intriguing architectural idea.
I find that fascinating.
After all, to us it was simply the warm floor where we sat during the
winter. ^^
Research on Frank Lloyd Wright's Experience of Ondol and Its
Architectural Application ---
KCI
7. Then Ondol-Like Heating Traces Were Found in Alaska
And here the story becomes even more interesting.
Following the trail of underfloor heating takes us across the Pacific
Ocean to Alaska's Aleutian Islands.
At the Amaknak Bridge site in Unalaska, archaeologists discovered
stone-lined channels running from hearths toward the interior of
dwellings.
A large excavation in 2003 uncovered structures that researchers
suggested may have been part of a sophisticated system designed to move
heat from a hearth beneath the floor.
Additional related features were investigated during excavations in 2006
and 2007.
Dating of the archaeological remains places them roughly within a range
of about 2,500 to 3,500 years ago.
One of the archaeologists who studied the site was Richard "Rick"
Knecht.
So how did similar ideas for heating floors appear so far away in the
Aleutian Islands?
Did people living in extremely cold regions independently arrive at
similar solutions because they faced the same basic problem---how to
survive the cold?
Or could ideas and technologies have traveled along with ancient human
migration?
There is an important point to keep in mind here.
The discovery of underfloor heating features in the Aleutian Islands
does not prove that Koreans traveled there and built ondol.
Based on the archaeological evidence currently available, we cannot
conclude that there was a direct transfer of heating technology between
the two regions.
And perhaps that uncertainty is exactly what makes the story so
interesting.
Sometimes a question that remains unanswered is more fascinating than a
story in which we already know everything.
Research on Hearths and Underfloor Channels at the Amaknak Bridge
Site
8. Want to See the Alaskan Heating Site for Yourself?
There is also a KBS documentary that explores this story.
"From the Korean Peninsula to Alaska: Following the Trail of the
Whale"
The documentary follows archaeological traces found in Alaska and
explores evidence found on the Korean Peninsula.
Ancient heating traces buried beneath the ground in Alaska.
What exactly did the researchers find there?
Sometimes it is much more interesting to see the place for yourself than
simply read about it.
KBS Documentary: From the Korean Peninsula to Alaska --- Following the
Trail of the Whale
9. Today, the Warmth of Ondol Is Crossing Oceans
By this point in writing about ondol, another question occurred to me.
Ancient ondol is fascinating, but what about today?
Do people outside Korea actually use Korean-style floor heating?
When I looked into it, I found real examples of Korean floor-heating
systems being exported and installed overseas.
According to a case introduced by Korea.net, the Korean government's
official website, a Korean company exported a hot-water floor-heating
system to ten countries, including Russia, Mongolia, Belarus, and
Ukraine.
The company's ondol-style floor heating was also installed in a
kindergarten in Belarus.
So the idea that Korean ondol technology is traveling overseas is not
merely an internet story.
There are actual cases of exports and installations.
Korea.net: Korean Ondol Overseas Export and Installation
Cases
10. What Happens When Korean-Style Ondol Is Installed in a Home in a Cold Country?
But lists of countries and export figures are not very exciting on their
own.
What does it actually look like when Korean-style floor heating is
installed in a home where people really live?
There is a video showing the installation of a modern Korean ondol
product in a Canadian home.
You can actually watch the process of installing modern Korean-style
floor heating in a house located in a cold climate.
One thing should be noted: the video was produced with support from an
ondol company, so it is worth keeping that in mind while watching.
Korean-Style Ondol Installation in a Canadian Home ---
Video
Watching that video brought back another memory for me.
My grandmother and mother used to feed straw and firewood into the
agungi.
When a room did not warm properly, my grandfather and uncle could open
up the gudeul floor and figure out what had gone wrong.
Today, things look very different.
Modern systems can use panels laid across the floor with hot-water pipes
running through them.
Some modern ondol products are even designed to be installed over an
existing floor or assembled using DIY-style installation methods.
This description is based on product and installation information
published by the manufacturer.
Modern Ondol Products and Installation
Examples
The warm floors that began with fires in agungi more than two thousand
years ago are now taking on new forms---panels and hot-water pipes---and
crossing oceans.
The technology has changed.
But what people want seems to be exactly the same as it was long ago.
A warm room.
11. How Many People Really Enjoy Being Cold?
While writing this article, another thought occurred to me.
How many people in the world truly enjoy being cold?
Plenty of people love a beautiful snowy winter landscape.
It is wonderful to watch fresh snow cover the ground, and many people
enjoy winter sports.
But I suspect there are far fewer people who actually enjoy shivering in
the cold all day.
When we come home from freezing weather, the desire to step into a warm
place is probably not very different whether we are Korean or from
somewhere else in the world.
It reminds me of my own childhood---running home with my frozen hands
tucked close to my body and diving straight into the warm bedding spread
over the araetmok.
For a very long time, our ancestors created that warmth through ondol.
My grandmother and mother lit the fire in the agungi.
My grandfather and uncle repaired the gudeul.
And our family gathered together on the warm araetmok to eat.
That old wisdom, passed down through generations, has now met modern
technology and is taking on new forms in other parts of the world.
I think there is something wonderful about that.
After all, there is no reason to keep something good entirely to
ourselves.
We can share what others need.
We can offer something useful from our own culture to our neighbors.
And we can learn from the good things our neighbors have to offer us.
Isn't that part of being good neighbors?
That is why I am glad to see 'Korean ondol' becoming known in other
countries and being adapted to the homes and lifestyles of the people
who live there.
There is no need to recreate an old Korean house exactly as it once was.
The idea can evolve into something more convenient and safer, suited to
the climate and homes of each country.
But if someone walking across a warm floor in a cold country today
receives even a small benefit from the wisdom that Koreans developed
long ago to survive bitter winters, I think that is something worth
smiling about.
Perhaps the warmth of the araetmok that comforted me during my childhood
can continue today in the home of a family somewhere in another cold
part of the world.
With the hope that we can become good neighbors by sharing good things
with one another,
I write this story today.
References and Further Reading
History and Characteristics of Traditional Korean Ondol (Gudeul) ---
KCI
Frank Lloyd Wright's Experience of Ondol and Its Application to His
Architecture ---
KCI
Amaknak Bridge Site Research --- Arctic Anthropology Related
Material
Korea.net --- More Than 2,000 Years of Ondol History and
Culture
Korea.net --- Korean Ondol Overseas Export and Installation
Cases
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