Green Heat Resources
Updated: June, 2022
A Visual, Schematic History of Wood Heating Technology
Wood heating technology has progressed slowly and unevenly throughout history. Little is known about how knowledge of wood heat was shared between regions and continents thousands, or even hundreds of years ago. To further complicate things, the history of wood heat is interwoven with the history of cooking, baking and kilns, all elements which helped propel our species to what it is today. Though fire has been an effective source of heat for millennia, the advancement of technology to separate heat from smoke was a radical public health development which also helped propel our species forward.
See our longer, less visual history of wood heat here.
This visual essay focuses in particular on technological advances in stove technology made during and after the 1980s; recognizing that an enormous amount of R&D toward sophisticated heating occurred well before then, and is often overlooked or lost to history. The development of cleaner and more efficient wood heating has not been a gradual, linear process. As a general rule, wood heat technology has advanced rapidly in times of deforestation and wood scarcity, and reverted to dirtier and less efficient heating when wood is abundant and cheap.
300,000 – 400,000 B.C.
Heating via burning wood likely began soon after fire was harnessed and used for cooking, by using rocks to radiate the flame.
The first evidence of kilns with controlled air flow, unlike earlier pit kilns, may have been around 2,000 B.C. It is unclear what relationship early kilns had to home heating, as kilns were developed first for making ceramics and then smelting of ores.
Contrary to some Euro-centric narratives, early stoves were used in Korea far earlier than in Rome, where they emerged around 350 B.C. These precursors to modern masonry heaters, called hypocausts, would circulate heat from an earthen and rock firebox below the floor of a room or through walls.
Though fires were built inside huts and homes for millennia, outside of hypocausts, chimneys did not appear in Europe until the 800s and were not widespread until the 1200s. The first metal heating stove may have been made in China, where advanced, high-carbon cast iron appeared around 100 A.D.
By the beginning of the 16th century, waterpower was used to blow air into bloomery furnaces, raising the temperature of furnaces to above 1,200°C (2,200°F), enabling stove production. The first stoves in Europe were likely crude fireboxes which were often in another room from where the stove was loaded. Like the original ondol from Korea, the earliest heating technology was likely paired with cooking.
Deforestation in Europe drove innovation, leading to early masonry heaters
. In these brick ovens, the smoke from small hot fires would be channeled through masonry mass, which would store the heat and release it over many hours.
While technically a step backward from the closed stoves that were already in use in Europe, Ben Franklin’s improved open fireplace
has garnered a place in the American imagination. Other innovators soon put a door on the front, significantly increasing its efficiency.
The 1800s were a time of exhaustive innovation which led to the creation of stoves that could heat, cook and even acted as ornate pieces of art.
Wood heating plummeted across America as cheap gas and oil took over, and stoves became far more basic and utilitarian. Many of these uncertified stoves
are still in use today
. Innovations from earlier centuries were cast aside, in favor of inexpensive, inefficient, and often dirtier burning appliances. Surviving elements of older stoves models included primary and secondary air vents, as well as baffles.
As wood stoves became popular again during the 1973 oil crisis, two iconic brands emerged. The Fisher stove, designed to be airtight, did not have any innovative combustion technology, but it had thick steel and a firebox large enough to hold a smoldering, overnight fire. Later in the decade, Vermont Castings, also built high quality, airtight stoves which were considered more modern.
In 1986, the state of Oregon began certifying wood stoves, followed by the EPA in 1988. The ensuing surge in innovation helped American wood heaters
get back toward levels of cleanliness and efficiency that masonry heaters had achieved hundreds of years before. Secondary air tubes, which brought pre-heated jets of air into the top of the combustion chamber, became nearly universal, which drastically reduced smoke.
In the 1990s, catalytic stoves
became popular for doing away with the secondary air tubes and adding a catalyst to reburn particulate matter before it went up the chimney.
The advent of pellet stoves
in the 2000s represented possibly the most drastic, innovative step in the history of residential heating. By separately designing its own, dry specific fuel and an automated mechanism to steadily meter the fuel into the firebox, user error could be reduced, making stoves cleaner and more efficient.
The 2010s saw the rise of the hybrid stove
, which used both a catalyst and pre-heated secondary air injected into the upper part of the firebox. This combination of technologies met the stricter 2015 EPA regulations.
The 2020s are beginning to see the emergence of automated wood stoves
, where sensors control primary and secondary airflow. This relieves the operator of much of the work, preventing smoldering and increasing efficiency. Another new development is the addition of sophisticated post-combustion control technologies like electrostatic precipitators (ESPs).
Integrating automated wood or pellet stoves with other renewables in a house offers homeowners the opportunity to choose which renewable is most available and cheapest to provide heat to the home and/or recharge energy storage units. Solar PV
, solar thermal
, heat pumps
, pellet stoves, and boilers provide a variety of energy production
options. In terms of energy storage, future innovation may produce more robust batteries for electricity or better storage options for hot water, but can’t beat nature’s battery – wood.