Laboratory furnace accessories are used to extend the capability of lab furnaces or to replace worn or damaged parts. A furnace temperature sensor, often a thermocouple, transmits the temperature inside the furnace to an outside display or a computerized controller in order to ensure that samples are exposed to the correct temperature. An external furnace temperature controller uses a thermocouple to monitor the internal furnace temperature. Analog or digital controls enable the operator to monitor, record, and adjust the temperature. Furnace hearth trays protect the bottom heating element from damage by falling particles and other debris, and furnace shelves extend capacity. Features to consider when selecting furnace accessories include the furnace size and capacity, materials processed, temperature range, and compatibility.