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Smudge pot

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A smudge pot is an oil-burning device used to protect fruit trees from frost.

Florida Smudge Pot
Florida Smudge Pot

These heaters are placed between trees in an orchard during cold snaps. The burning oil generates heat, smoke, carbon dioxide, and water vapor. This process helps prevent the orchard from cooling too much. While primarily used in agriculture, they have served many other purposes. They have warmed large buildings, lit remote airfields, and even protected military targets.

Smudge Pot Patent
Smudge Pot Patent

The basic mechanism involves a large round base with a chimney in the center. To start the device, a piece of oil-soaked wood called a down-draft tube and wick is secured inside the neck. When the air temperature drops, a farmer uses a draft regulator to control the burn. This regulator is a filler cap with a three- or four-hole flue control. As the temperature decreases, the farmer opens more holes to increase the heating effect. However, once the temperature falls below 25 degrees, no further heating enhancement is possible.

There are two major styles of these orchard heaters. The first style consists of a single louvered stack sitting above a base filled with fuel oil. The second, more advanced version is a taller model featuring a cambered, louvered neck. This version includes a galvanized re-breather feed pipe on the side of the chimney. This pipe siphons stack gas back into the burn chamber. This process results in more complete combustion. This specific return-stack heater was developed by the University of California and became available around 1940.

In Australia, these devices are known as "choofers" because of the noise they make when lit. The name comes from the "choofa choofa choofa" sound they produce. Lighting a choofer is a delicate process because they produce thick, oily black smoke when cold. A person must light them outside by holding a burning rag near the open damper. The breeze creates a draught that pulls air through the chimney and into the fuel tank. Once the fuel surface ignites, the heater becomes steady. If the damper is not closed, the pot may choke on its own smoke and cause noisy explosions of unburnt gases.

The history of the smudge pot is tied to the inventor Willis Frederick Charles "W.C." Scheu. In 1907, while living in Grand Junction, Colorado, Scheu developed an oil-burning stack heater. He found it was more effective than using open fires to heat vineyards and orchards. In 1911, he opened the Scheu Manufacturing Company in Upland, California. His company, Scheu Steel, remains in business as of 2021. The use of these pots became widespread following a disastrous freeze in Southern California from January 4 to 8, 1913. This freeze wiped out entire crops and proved the value of the device.

The scale of smudge pot use in the early 20th century was massive. In the Redlands district, there were 462,000 orchard heaters for the winter of 1932–33. To refill these heaters just once required 3,693,000 gallons of oil. This amount of fuel is equal to about 330 tank-car loads. To fill every smudge pot in Southern California a single time required 2,000 carloads of oil. Use of the pots eventually declined in the 1970s. This was due to rising oil prices and increasing environmental concerns.

Smudge pots have also played roles in military history and unexpected social traditions. During World War II, the German, Japanese, and United States Navies used them. In the Vietnam War, North Vietnamese forces used them to protect valuable targets. The thick smoke from the pots could diffuse laser beams. This broke the connection between a laser-guided bomb and its intended target. Today, the smudge pot is even a symbolic prize in California high school football. Two rivalries involve playing for a silver-plated or a blue-and-red smudge pot. One famous game is even called the "Smudge Bowl."

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File:Florida Smudge Pot.JPG
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Smudge Pot Patent.jpg
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