Different types of donut fryers are often categorized based on the way in which heat is generated or the surface on which they are meant to be placed. Both electric and gas fryers are commonly available, which use different types of power supplies to create the heat necessary to bring the frying oil up to a sufficient temperature. Floor model fryers are typically those that are meant for professional or commercial use, which stand on the floor and are quite tall. There are also countertop donut fryers that can be used both commercially and in a home kitchen and stand on a countertop rather than on the floor.
Donut fryers heat up vats of oil into which donut dough or batter is placed for frying. Commercial models of these appliances are often quite large and can include numerous vats of hot oil and a conveyer belt that moves donuts along the fryer. These devices can include a cooling area that allows the donuts to cool off slightly before they are dipped into glaze or covered with various toppings. Home kitchen donut fryers are typically quite a bit smaller, usually intended for only a few donuts to be fried at once, and do not necessarily include a cooling area.
One common way in which donut fryers can be organized is by the way in which heat is applied to the oil. Electric fryers typically connect to a wall outlet, such as that found in a home kitchen or commercial bakery. Heating coils powered by electricity cause the oil in vats to increase in temperature, which is used to cook the donuts. There are also gas donut fryers which are often used at fairs and other events without reliable or available electrical outlets, which use gas-fueled fires to heat the oil.
Donut fryers can also be categorized based on the type of surface in which they are usually placed during operation. A floor model or floor stand fryer is large enough that its feet are on the floor of a room. These fryers are quite tall, usually supported on legs or a large frame, and many commercial models are available in this style. Countertop donut fryers, on the other hand, are shorter and can be placed directly onto a counter, rather than supported on legs. Larger versions of these models are available for use in professional bakeries, though smaller countertop fryers are often preferred for home kitchens.