The Franklin stove
is a metal-lined fireplace
A fireplace is an architectural structure to contain a fire for heating and, especially historically, for cooking. A fire is contained in a firebox or firepit; a chimney or other flue allows gas and particulate exhaust to escape...
named after its inventor, Benjamin Franklin
Dr. Benjamin Franklin was one of the Founding Fathers of the United States. A noted polymath, Franklin was a leading author, printer, political theorist, politician, postmaster, scientist, musician, inventor, satirist, civic activist, statesman, and diplomat...
. It was invented in 1741.
[L.W. Labaree, W. Bell, W.B. Willcox, et al., eds., The Papers of Benjamin Franklin (New Haven, Connecticut: Yale University Press, 1959-1986), vol. 2, page 419.]
It had a hollow baffle near the rear (to transfer more heat from the fire to a room's air) and relied on an "inverted siphon" to draw the fire's hot fumes around the baffle.
[Samuel Y. Edgerton, Jr., "Supplement: The Franklin Stove" in I. Bernard Cohen, Benjamin Franklin's Science (Cambridge, Massachusetts: Harvard University Press, 1990), pages 204-206.]
It was intended to produce more heat and less smoke than an ordinary open fireplace. It is also known as a "circulating stove" or the "Pennsylvania fireplace".
The two distinguishing features of Franklin's stove were a hollow baffle and a flue that acted as an inverted siphon.
In Franklin's stove, a hollow baffle was positioned inside and near the rear of the stove. The baffle was a wide but thin cast-iron box, which was open to the room's air at its bottom and at two holes on its sides, near its top. Air entered the bottom of the box and was heated both by the fire and by the fup[opi flowing over the front and back of the box. The warmed air then rose inside the baffle and exited through the holes in the baffle's sides. The use of baffles to extract more heat from a fire and its fumes was not new. In 1619, Franz Keslar of Frankfurt-am-Main, Germany published Epargne Bois
... (The Wood Saver), featuring a stove in which the fumes from a fire were forced to snake through eight chambers, one above the other, before entering the chimney. In 1624, a French physician, Louis Savot (1579–1640), described a fireplace that he had built in the Louvre. Ducts passed under, behind, and above the fire in the hearth. Cool air in the room entered the lower opening of a duct, was warmed, rose, and returned to the room through the duct's upper opening. In 1713, Frenchman Nicolas Gauger (ca. 1680-1730) published a book, La Mechanique du Feu
... (The Mechanics of Fire), in which he presented novel designs for fireplaces. Gauger surrounded the hearth with hollow spaces. Inside these spaces were baffles. Cool room air entered the spaces through lower openings, was warmed as it snaked around the baffles in the spaces, and returned to the room through upper openings.
Some early experimenters reasoned that if a fire in a fireplace were connected by a U-shaped duct to the chimney, the hot gases ascending through the chimney would draw the fire's smoke and fumes first downwards through one leg of the U and then upwards through the other leg and the chimney. This was what Franklin called an "aerial syphon" or "syphon revers'd". This inverted siphon was used to draw the fire's hot fumes up the front and down the back of the Franklin stove's hollow baffle, in order to extract as much heat as possible from the fumes. The earliest known example of such an inverted siphon was the 1678 fireplace of Prince Rupert
Rupert, Count Palatine of the Rhine, Duke of Bavaria, 1st Duke of Cumberland, 1st Earl of Holderness , commonly called Prince Rupert of the Rhine, KG, FRS was a noted soldier, admiral, scientist, sportsman, colonial governor and amateur artist during the 17th century...
(1619–1682). Rupert placed a hanging iron door between the fire grate and the chimney. In order to exit through the chimney, the fire's fumes and smoke first had to descend below the edge of the door before rising through the chimney.
[Charles Tomlinson, A Rudimentary Treatise on Warming and Ventilation ... , 3rd ed. (London, England: Virtue Brothers & Co., 1864), pages 85-86.]
Another early example of an inverted siphon was a stove that was exhibited in 1686 at a fair in St. Germains, France. Its inventor, André Dalesme (1643–1727), called it the "furnus acapnos" (smokeless stove). The stove consisted of an iron bowl in which the fuel was burned. A pipe extended from the bowl's bottom and then upwards into a chimney. Shortly after starting a fire in the bowl, hot air would begin to rise through the pipe and then up the chimney; this created a downward draft through the bowl, which drew the fire and its fumes down into the bowl. Once the draft was initiated, it was self-sustaining as long as the fire burned. Dalesme's stove could burn wood, incense, and even "coal steept in cats-piss" yet produce very little smoke or smell. These results showed that fires could be used inside a room, without filling the house with smoke.
Gauger's book on his innovative fireplace designs was translated into English -- Fires Improv'd: Being a New Method of Building Chimneys, So as to Prevent their Smoaking
(1715) -- by a French immigrant to England, Jean Théophile Desaguliers
John Theophilus Desaguliers was a natural philosopher born in France. He was a member of the Royal Society of London beginning 29 July 1714. He was presented with the Royal Society's highest honour, the Copley Medal, in 1734, 1736 and 1741, with the 1741 award being for his discovery of the...
(1683–1744). In a postscript to Desaguliers' book A Course in Experimental Philosophy
(1744), Desaguliers again briefly described Gauger's fireplaces and mentioned his own work on the subject. Franklin read both of Desaguliers' books and developed his own designs for a stove that could provide more heat with less smoke.
In 1742, Franklin finished his first design which implemented new scientific concepts about heat which had been developed by the Dutch physician Herman Boerhaave
Herman Boerhaave was a Dutch botanist, humanist and physician of European fame. He is regarded as the founder of clinical teaching and of the modern academic hospital. His main achievement was to demonstrate the relation of symptoms to lesions...
(1668–1738), a proponent of Isaac Newton's ideas. Two years later, Franklin wrote a pamphlet describing his design and how it operated in order to sell his product. Around this time, the deputy governor of Pennsylvania, George Thomas, made an offer to Franklin to patent his design, but Franklin never patented any of his designs and inventions. He believed “that as we enjoy great advantages from the inventions of others, we should be glad of an opportunity to serve others by any invention of ours, and this we should do freely and generously”. As a result, many others were able to use Franklin’s design and improve it. Although his stove was intended to have the double purpose of cooking and heating a room, as time progressed and new stove designs became available, the Franklin stove’s main use became to heat a room. Many others improved on the Franklin stove design, but to this day, most American fireplaces are box-shaped, similar to the Franklin stove. The exception is the Rumford fireplace
The Rumford fireplace is a tall, shallow fireplace designed by Sir Benjamin Thompson, Count Rumford, born 1753 in Woburn, Massachusetts, an Anglo-American physicist who was known for his investigations of heat....
, developed by Benjamin Thompson.
The height of the stove was about 30 inches tall with a box shape. The front side was open, except for a decorative panel in the upper part of the box. The back of the box was to be placed a few inches away from the flue, or chimney. On the bottom panel there were several holes to allow the smoke to escape; these were connected to the chimney. These panels were bolted together with iron screws through pre-cast ears. A picture of the different pieces can be found here
Inside there was a small thin rectangle prism that would force the smoke into the holes. The plates were all made from iron.
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- Rogers, Jr. et al.. Franklin Stove. . 26 Oct. 1965.
- Franklin, Benjamin. "The Autobiography of Benjamin Franklin." Archiving Early America: Primary Source Material from 18th Century America. Web. 14 Nov. 2010.