Smudge pot

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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 1913 wiped out a whole crop.^{[citation needed]}

Smudge pots were commonly used for seven decades in areas such as California's numerous citrus groves.^{[citation needed]} The smudge pot often became a symbolic prize in local football rivalries. Today rivals Bonita High School and San Dimas High School, in Southern California, compete for a silver-plated smudge pot, and in Redlands, California, Redlands High School and Redlands East Valley High School compete for a blue-and-red pot.

Smudge pot use in Redlands 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 an 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 — "choofa choofa choofa".

Lighting an Australian "choofer" is a tricky business. Because of the voluminous clouds of oily black smoke they produce when cold, they must be lit outside. This is accomplished by holding a burning rag next to the open damper on the fuel tank. The draught caused by the breeze passing through the chimney will draw the flames through the open damper into the fuel tank, where the surface of the fuel inside will light and burn instantly. Once the choofer is sufficiently warm, the damper may be closed until a steady rate of burning is attained, when the characteristic "choofa choofa choofa" noise is produced. If the damper is not closed, the choofa may choke itself with its own smoke, causing periodic "explosions" of unburnt gases in the chimney. Such explosions are not dangerous, but they are noisy and they produce a lot of smoke. Once the heater is burning hot enough, the smoke will disappear and the pot may be dragged slowly and carefully inside. They still produce dangerous gas, and must only be used in well-ventilated spaces.

Choofers will burn almost any flammable liquid fuel, including kerosene, diesel fuel, or used sump oil.