Nordic inventions: Patents for the sauna stove

Saunas are essential for providing warmth, mostly during cold winters, and are a key aspect of Nordic culture, especially in Finland where there are 3.2 million of them. The most important element of saunas is the stove that is used to heat them up. 

This article is part of our series on Nordic inventions, and it explores the history and development of sauna stoves, highlighting the people who patented them.

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The journey to today's sauna

Saunas have been a part of people's life in Finland, where they were invented, for over 2000 years. Let's have a quick look at the history and heating methods of saunas to see how these inventions came to life.

Originally, saunas were primitive earth pits, covered with animal skins for insulation. In the Stone Age, ground saunas emerged as a simple yet effective means of heating. Constructed with minimal materials—earth floors, three walls, a wooden door, and a turf roof supported by tree trunks—these saunas featured a corner stove and log benches for seating.

The creation of the smoke sauna marked a significant advancement in sauna technology during the Iron Age. In a smoke sauna (known as "savusauna" in Finnish), the rocks were heated (for 6 to 8 hours) directly by the fire under them. Once the rocks reach the desired temperature, the fire was extinguished, and the sauna chamber was left to ventilate for a period before it was deemed safe for use. Once the smoke cleared, they were able to provide warmth for hours. Despite the later technological advancements, these saunas remained widely used up until the 1930s.

The introduction of sauna stoves with chimneys in Western Finland during the 18th and 19th centuries revolutionized sauna heating. This innovation quickly spread, paving the way for the barrel-shaped, sheet metal stoves that defined sauna technology in the 20th century.

In the aftermath of World War II, a new era of sauna heating emerged with the advent of small electric and gas-heated stoves, specifically in the 1950s. This fifth generation of stoves drastically reduced heating times, allowing saunas to be ready for use in just half an hour. Today, these efficient stoves continue to be a staple in many Finnish cottages and backyard saunas, representing the enduring legacy of Finnish sauna culture.

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The pioneer in sauna stove invention
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The most important person in the innovation of the sauna stove is Fredrik Terho, who secured the first patent for a sauna stove in 1910 - Finnish patent 4010. Recognized for his innovative approach to crafting iron stoves, Terho's method involved the construction of the stone and smoke compartments using sheet iron.

In detail, he manifested in the narrowing of the top of the stone and smoke compartment above the firebox, creating a smoke flue covered by a hatch. This flue led to a masonry chimney, which could be closed using a register plate. This ingenious design eliminated the need for bulky and heat-retaining masonry, resulting in a lighter, quicker-to-heat, and more cost-effective sauna stove.

In the same year, along with a similar metal-cased stove (Finnish patent 4090) equipped with a hot water tank, laid the foundation for industrially manufactured heat-storage barrel stoves, widely popular in the early 20th century. 

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Other sauna stove related patents
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In the 20th century, Finland experienced an invention boom when it came to saunas, with some other honorable mentions in the patented category:

• In 1933, John Backman patented a unique sauna stove. It had a special element above the firebox for stones. These stones were heated indirectly, beneath a metal surface, allowing users to pour water on them even while the fire burned below. This stove, known as the continuous fire stove, was compact and great for smaller saunas. It also kept the soot inside the stove, making it easy to clean, making it very popular in the early 20th century.
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• Väinö Savolainen's electric sauna stove patent (Finnish patent 24221) in the 1930s replaced traditional stones with iron blocks. 
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• Kari Vikström's electric stove with sauna stones (Finnish patent 29081) in 1957 revolutionized sauna design, enabling saunas to be installed in multi-story apartment buildings, causing the widespread adoption of apartment saunas. 
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• Lastly, the sauna stove protected by Finnish patent 83157 by Helo Oy facilitated continuous heating with minimal power consumption, eliminating the need for prolonged pre-heating in the 1980s.
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The sauna stove's journey captures the spirit of Finnish innovation and resilience against the cold, from Fredrik Terho's pioneering designs to the several other adjustments shaping the sauna stove technology. Its global recognition, propelled by the electric stove's invention, signifies the universal appeal of this Nordic tradition.

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