A smudge pot (also known as a choofa or orchard heater) is an oil-burning device used to prevent frost on fruit trees. Usually a smudge pot has a large round base with a chimney coming out of the middle of the base. The smudge pot is placed between trees in an orchard, allowing the heat and smoke from the burning oil to prevent the accumulation of frost on the fruit of the grove. Smudge pots were developed after a disastrous freeze in Southern California in January 1913 wiped out a whole crop.
Smudge pots were commonly used for seven decades in areas such as California's numerous citrus groves.
Smudge pot use in Redlands, California groves continued into the 1970s, but fell out of favor as oil prices rose and environmental concerns increased. Pots came in two major styles: a single stack above a fuel oil-filled base, and a slightly taller version that featured a cambered neck and a re-breather feed pipe out of the side of the chimney that siphoned stack gas back into the burn chamber and which produced more complete combustion. Filler caps have a three- or four-hole flue control. The stem into the pot usually has a piece of oil-soaked wood secured inside the neck to aid in lighting the pot. Pots are ignited when the air temperature reaches 29 degrees Fahrenheit, and for each additional degree of drop, another hole is opened on the control cap. Below 25 degrees, there is nothing more that can be done to enhance the heating effects.
Some groves used natural gas pots on lines from a gas source, but these are not "smudge pots" in the usual sense, and they represented only a fraction of the smudging practice. Sometimes, large smudge pots are used for heating large open buildings, such as mechanics workshops. In Australia they are called "choofers" because of the noise they make when lit ó "choofa choofa choofa".
Choofers will burn almost any flammable liquid fuel, including kerosene, diesel fuel, or used sump oil.
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