The fire – which we have used in our homes for over 400,000 years – remains the most versatile and sustainable household technology that humanity has ever known. The fire alone provided what we now get through a combination of modern appliances such as the oven and cooking hob, heating system, lights, refrigerator, freezer, hot water boiler, tumble dryer, and television. Unlike these newer technologies, the fire had no need for a central infrastructure to make it work, and it could be built locally from readily available materials.
Illustration: Diego Marmolejo.
From Open Hearth to Power Plant
The habitual use of fire dates back at least 300,000 to 400,000 years. [1-2] Until the twentieth century, the biomass-fuelled fire was the only energy using “appliance” in the household – whether people were living in a cave, a temporary hut, or a permanent building. The earliest shelters were often erected with the express purpose of keeping fire alive, protecting it from wind and rain.
For most of history, the fire appeared in the form of an open hearth, which was built on an earthen floor in the middle of a shelter. The smoke of the fire escaped through a hole in the roof. Beginning in the fourteenth century in Europe, the open hearth was gradually replaced by a fireplace connected to a chimney, most often built against a wall. In colder regions (such as Scandinavia), people built more energy efficient tile stoves, while in milder climates (such as those around the Mediterranean), people continued to use braziers – portable metal baskets in which charcoal was burnt. In the 18th and 19th centuries, fireplaces were starting to be replaced by metal stoves.
The fire remained central in the household until the 20th century, when it was replaced by a wide range of appliances, plugged into central infrastructures. Today, in industrial societies, even metal stoves have become rare in households. Open burning has been all but banned, especially in cities. New buildings no longer have fireplaces, chimneys, or a hole in the roof.
“Paradoxically”, writes Luis Fernández-Galiano in Fire and Memory: On Architecture and Energy, “the dwellings that began as places to promote the fire, today shun open burning”.  In Fire: A Brief History, Stephen J. Pyne observes that: “Urban residents can pass years without seeing a fire. It appears mostly by accident or arson, and almost always as a danger”. 
However, the fire has far from disappeared. Thousands of individual fires in households have been replaced by a few giant fires in central power plants. And the fire also burns elsewhere. “In our economy of abundance”, writes Stephen J. Pyne, “fire is at the heart of the magic – in factories, automobiles, homes and power plants… Modern cities remain fire-driven ecosystems… Shut down combustion and you shut down the city. But open flame itself has vanished. Like a black hole in space, fire has shaped everything around it without itself being visible.”
Industrialisation has only altered, not abolished burning. Most importantly, fire started using another energy source: fossil fuels instead of biomass. Until the twentieth century, almost all human-made fires were the product of renewable energy sources: wood, grass, dung – peat and some early uses of coal being the exceptions. Today in industrial societies, almost all fire “at the heart of the magic” burns on gas, coal or oil.
Fire vs. Electricity
Globally, a few billion people still live in households built around an old-fashioned fire, often in the form of an open hearth. Some people in the Western world consider this a backward and primitive practice that needs to be abolished – even though it is based on the use of renewable energy sources. For example, in 2011, the UN and the World Bank launched the Sustainable Energy for All initiative, aiming to “ensure universal access to modern energy services” by 2030.  The concept of “modern energy services” is vague, but it essentially refers to the use of electricity and gas – and thus, in practice, the use of fossil fuels.
Initiatives like this imply that “modern energy services” are “better” than the traditional open hearth or fireplace. “Urbanites see fire as a technology for which other, more advanced technologies can substitute”, writes Stephen J. Pyne. “If fire is a device, they want an improved flame- and smoke-free upgrade”. Examples of such flame- and smoke-free upgrades are today’s solar PV panels and wind turbines, which are supposed to end our dependence on fossil fuelled fires to produce “modern energy services”. However, how do open hearths and “modern energy services” – including those based on renewable energy sources – actually compare in terms of efficiency, sustainability, health and safety? What are we really saying when we argue that electricity or gas are “better” than a traditional fire?
The Versatility of a Fire
One reason why people in industrial societies regard open fire as inefficient and unsustainable is because they simply don’t know how their ancestors actually used it. If these days a fire is considered to be inefficient, it’s because we only measure the efficiency of one of its functions, usually space heating. However, our ancestors did not only use the fire to warm themselves. They also used it for cooking, illumination, food preservation, hot water production, clothes drying, and protection from predators and insects, among other things.
Illustration: Diego Marmolejo.
Fire is extremely versatile: it’s hard to say which of its functions were most valued by our ancestors. Therefore, if we measure the energy use of a household fire and compare it to modern technology, we should not compare it to the energy use of a heating system or a cooking stove alone, but to the energy use of the entire household.
Cooking With Fire
As a cooking device alone, the fire can accommodate a wide variety of cooking methods and replace a surprisingly large number of modern kitchen appliances. The fire not only functioned as a cooking stove, but also as an oven. For roasting and grilling, food was held on a turning spit and cooked by direct exposure to the fire. Baking happened in a clay container (a “Dutch oven”) which was put in the ashes of the fire. Alternatively, a separate bake oven was built into the jamb or the rear of the fireplace, or as a freestanding structure outside the house. Boiling and frying happened in a pot that was hanging above the fire. [6-7]
The functions of many smaller electrical kitchen appliances were also enabled by the fire. For example, you may think that people started eating toast when the electric toaster appeared in the twentieth century, but before that time they simply held a “toasting fork” into the fire. Likewise, quickly preparing warm drinks did not begin with the invention of the electric immersion heater: earlier on, people immersed a red-hot iron tool in a cup, producing hot beverages in a matter of seconds. 
The fire also substituted for today’s refrigerator and freezer. In The Food Axis: Cooking, eating, and the architecture of American houses, Elizabeth Collins Cromley describes how meat and fish were suspended for several weeks in the smoke of a fire to preserve them for longer.  At the simplest level, our ancestors hung their cuts of meat or fish in the kitchen chimney or – if there was no chimney – high above the hearth, suspended from the ceiling. Smoking fish and meat could also happen in a chimney smoke chamber, which was either an adjunct to the kitchen fireplace, or a chamber built off the chimney in the basement or attic. The smokehouse could also be a separate building.
Several other food preservation methods were dependent on fire. Fruits, vegetables and herbs were dried by fire if the local climate wasn’t sunny enough. Sugaring fruits and making butter and cheese all depended on heat from a fire. Salt, essential for food preservation, was kept in a box hung against the fireplace to keep it dry. 
Distributing Heat and Light
A fire not only produces heat and smoke – it also produces light. As a light source, fire was just as versatile as electric lighting is today. The light of a fire resided not only in the hearth or the fireplace, but also in torches, rushlights, and later candles and oil lamps. [9-10] Heat from a fire could also be spread all over the household. Although the kitchen was usually the only space in the house that was heated, embers from the fire could be put into portable heating devices, such as foot stoves and bed warmers. 
The fire was also used to heat water for cleaning and washing, a practice that continued when cast-iron wood-stoves appeared – many of these had hot water tanks. Furthermore, the fire took care of drying clothes, substituting for today’s tumble dryer. And people didn’t just start ironing their clothes when the electric iron came along. Since the middle ages, our ancestors used plain metal irons that were heated by a fire or on a stove, or a “box iron”, which held glowing charcoal inside – some of these had a small chimney to keep smokey smells away from the clothes. 
There was also the function of the fire as a focal point of communication and socialisation. For thousands of years, the hearth was the “ancient focus of conversation and the crackling soul of the house”.  Televisions and mobile phones have taken over these roles, although it is doubtful whether they hold the same appeal for people as a fire does. A host of electronic consumer products that imitate the effects of a fire – electric candles and fireplaces, led-bulbs with flickering flame effects, video’s of crackling fires – seem to indicate that humans miss open fire.
Sustainability and Efficiency
In a household built around a fire, the making of hot beverages and toast, the drying of clothes, or the illumination of the space does not raise the energy use of the fire: it simply makes more efficient use of the fire that is already there for other purposes – like space heating. To achieve the same result today, we have to turn on a several appliances, and all of them require extra energy use: the heating system, the immersion heater, the electric toaster, the tumble dryer, and the lights.
Furthermore, we should also take into account the mining and the energy use required to replace one fire with dozens of factory-made appliances, which all need to be distributed to individual consumers. Finally, we should take into account the energy and materials that are required to build and maintain the infrastructures that these appliances depend on to operate, like the power grid, gas infrastructure, or the cold chain. In contrast, an open hearth can be built locally with readily available materials, and it operates independently of centralised infrastructures.
Illustration: Diego Marmolejo.
Today’s renewable power plants, such as solar PV panels or wind turbines, don’t properly address the energy question: they also need to be manufactured, transported, maintained and discarded of, and they imply that we can keep designing, producing and discarding an increasing range of electric household appliances in order to satisfy our needs. Neither would biomass electricity make this system sustainable: although it eliminates the use of fossil fuels, a great deal of energy is lost in the process of converting biomass to electricity, and we still need factories to manufacture the electric appliances and the infrastructures.
Energy Use Compared: Ancient vs. Modern Households
If we look at the energy use in European households today, we see that on average 64% of all energy goes to space heating, 15% to water heating, 14% to lights and appliances, 5% to cooking and 1% to other services (including cooling).  Most of these services can be supplied by fire. So, how does the energy use of a traditional household with open hearth compare to the energy use of a modern household built around appliances and infrastructures?
Obviously, the energy use of modern houses is better documented than that of buildings and shelters from times gone by. However, there is research documenting the energy use of households that still rely on a traditional fire.
A 2002 investigation of firewood consumption in traditional houses in Nepal measures the annual firewood consumption per household to be between 6 and 33 m3, which corresponds to between 35 and 165 Gigajoule (GJ) of energy. [14-16] This seems quite a lot in comparison to the total energy use in contemporary households, which is around 75 GJ per year in Germany and around 105 GJ in Canada.
However, the average Nepalese household participating in the research consisted of 5 to 12 people, while households in modern societies have shrunk to little more than two people. In the Nepalese households under study, energy use was between 2 and 33 GJ per capita, while another, more recent research paper on firewood consumption for heating, cooking and lighting in Nepal calculates a per capita use of roughly 2.5 to 10 GJ of energy per person per year. [17-18] In comparison, total household energy consumption per capita is around 30 to 40 GJ in countries like the Netherlands, Germany and Canada.
10 Billion People Around the Hearth
Even without taking into account the extra resources needed to build the appliances and the infrastructures, energy use in the pre-industrial household seems to have been significantly lower than it is today. In fact, a quick calculation reveals that – at least in theory – 10 billion people using an open hearth as their only energy source would be a perfectly sustainable practice.
Assuming an average firewood consumption of 6 m3 per capita, we would need 60 billion cubic metres of wood annually. One cubic metre of wood requires an annual yield of 0.2 ha of coppice, so we need 12 billion ha or 120 million square kilometers of forest if we want to avoid deforestation. That’s three times as much as we have today, and about 80% of the total land area of our planet (150 million square kilometers). Because we don’t need extra space for factories and roads to make and distribute consumer goods, we actually could go back to the open hearth without destroying our environment. The same cannot be said of 10 billion people going forward using fossil fuels and modern infrastructures.
Health vs. Sustainability
If not for their sustainability or efficiency, then why do we consider “modern energy services” superior to a traditional fire? The suppression of open fire in modern cities is supported by two extra arguments: fire is unhealthy (it produces air pollution), and it is dangerous (it carries the risk of an uncontrollable fire). These risks are real, but how does the fire compare to “modern energy services” in terms of health and safety?
There is no doubt that the replacement of the household fire by modern infrastructures has advanced air quality, health and safety in cities. However, this may only be a temporary gain: modern infrastructures are at least as hazardous to safety and health because of their dependence on fossil fuels.
For example, the heat waves and forest fires which are ravaging Australia while I write this, are killing people and destroying properties, and they are producing thick smoke that continues to blanket some of the largest cities. These fires are not caused by people using open hearths. These fires are the consequence of climate change, which is mainly caused by people’s use of industrial infrastructures – powered by fossil fuels.
The heavy dependence on central infrastructures for so many vital needs is another health and safety risk: cut the power supply to a large city and almost everything stops working — including the sewer network, the food storage, and the burglar alarms.
Our troubled view of the old-fashioned fire is partly rooted in the conflation of two distinct concepts: “health” and “sustainability”. Indeed, something can be healthy, safe and sustainable at the same time, like walking – lest there is no sidewalk. But something can also be healthy and safe but not very sustainable (like a refrigerator, because it depends on an energy-intensive cold chain), and something can be sustainable but not very healthy or safe (like a smokeroom for meat and fish in the basement).
Health and longevity are things that we, as individuals, “need”, want, desire, or feel entitled to. Just like we feel entitled to certain levels of comfort, convenience, speed or cleanliness. On the other hand, defining sustainability requires us to question what levels of human comfort, convenience, cleanliness, speed, safety and health our environment can support before it collapses. We can choose safety and health over sustainability when they are in conflict with each other, but only at the expense of the safety and health of younger and future generations.
References & Notes:
 Roebroeks, Wil, and Paola Villa. “On the earliest evidence for habitual use of fire in Europe.”. Proceedings of the National Academy of Sciences 108.13 (2011): 5209-5214.
 Berna, Francesco, et al. “Microstratigraphic evidence of in situ fire in the Acheulean strata of Wonderwerk Cave, Northern Cape province, South Africa.” Proceedings of the National Academy of Sciences 109.20 (2012): E1215-E1220.
 Fernández, Guillén, and Luis Fernández-Galiano. Fire and memory: on architecture and energy. Mit Press, 2000.
 Pyne, Stephen J. Fire: a brief history. University of Washington Press, 2019.
 Collins Cromley, Elizabeth. The food axis: cooking, eating, and the architecture of American houses. University of Virginia Press, 2010.
 Unlike today’s gas or electric stoves and ovens, a fire has no buttons to control its temperature. For boiling and simmering, this was solved by hanging the pots on a crane, which could be raised or lowered. In ovens, cooks decided to bake pies or bread first while the oven is the hottest, then, successively as the oven cools down, gingerbread, custards, then grains could be put in to dry. 
 Marcoux, Paula. Cooking with fire: From roasting on a spit to baking in a tannur, rediscovered techniques and recipes that capture the flavors of wood-fired cooking. Storey Publishing, 2014.
 Hough, Walter. Fire as an agent in human culture. No. 139. Govt. print. Off., 1926.
 The energy source for these distributed fires were wood, resin, wax, fat, grease or oil. Needs for special concentration and position of the source of illumination stimulated the invention of holders, brackets, and stands. 
 Heating people, not spaces: restoring the old way of warming, Kris De Decker, Low-tech Magazine, 2016.
 History of ironing, Old & Interesting, retrieved December 26, 2019.
 Energy consumption and use by households, Eurostat, 2019.
 Rijal, H. B., and H. Yoshida. “Investigation and evaluation of firewood consumption in traditional houses in Nepal.” Proceedings: Indoor Air (2002): 1000-1005.
 The energy content of 1 m3 of wood also depends on the type of wood and how it is stacked. I’ve compared apples to apples when it was possible, but this was not always the case so the result is only a rough estimate.
 The annual firewood usage in 18th century Austria (Carinthia) was limited to 35 m3 per household. Source: Peter, Sieferle Rolf. The subterranean forest. Cambridge: The White Horse Press, 2001.
 Rijal, Hom Bahadur. “Firewood Consumption in Nepal.” Sustainable Houses and Living in the Hot-Humid Climates of Asia. Springer, Singapore, 2018. 335-344.
 The results are 0.5 to 2 m3 of firewoord per person per year, which I have converted to 2.5 to 10 GJ of energy per person per year.